Surface faulting of the 6 April 2009 Mw 6.3 L’Aquila earthquake in central Italy

Surface Faulting of the 6 April 2009 Mw 6.3 L’Aquila

Earthquake in Central Italy

by Eutizio Vittori, Pio Di Manna, Anna M. Blumetti, Valerio Comerci, Luca Guerrieri,Eliana Esposito, Alessandro M. Michetti, Sabina Porfido, Luigi Piccardi, Gerald P. Roberts,

Andrea Berlusconi, Franz Livio, Giancanio Sileo, Max Wilkinson, Kenneth J. W.McCaffrey, Richard J. Phillips, and Patience A. Cowie

Abstract This paper documents evidence of surface faulting associated with the 6April 2009 moderate-sized earthquake (ML 5.8, Mw 6.3) in the central Apennines ofItaly, which caused major damage to the town of L’Aquila and its surroundings.Coseismic surface ruptures were mapped for a minimum distance of 2.6 km alongthe Paganica fault, a fault still poorly investigated relative to the other active faultsnearby, which bound much wider range fronts. Surface rupture length (SRL) andmaximum displacement parameters (2.6 km minimum and 10–15 cm, respectively)are in agreement with what is expected for an Mw 6.3 event in the Italian Apenninestectonic environment. Different viewpoints exist on the amount of SRL and the num-ber of activated faults. We propose a pattern of sympathetic and secondary slip on anarray of faults around the master seismogenic structure. Past seismicity and evidencefor larger Holocene offsets on this and other capable faults nearby prove that the 2009event is not a good reference event for assessing the seismic hazard of the region.Nevertheless, the 2009 L’Aquila earthquake once more confirmed the importanceof detailed geological studies for a proper seismic hazard assessment, and it clearlyillustrates the need to pay attention to moderate events and supposedly minor activefaults. Indeed, this type of earthquake is rather frequent in the whole Mediterraneanregion and is potentially much more destructive than in the past, due to the expandingurban centers and infrastructures inside their epicentral regions and even right abovethe traces of capable faults.

Introduction

In the night of 6 April 2009, a moderate-sized earth-quake (ML 5.8, Mw 6.3, depth 9 km) rocked the centralApennines in central Italy (Fig. 1), after several months ofmounting seismic activity focused in the L’Aquila basin(Chiarabba et al., 2009). The epicenter for the mainshockwas located near the historical town of L’Aquila (Fig. 1),which, together with many villages in the surrounding area,was severely damaged. The death toll reached 308, a numberthat could have been larger if an ML 3.9 foreshock had notheralded the main event a few hours previously, keepingmany residents out of their homes for the night. Several tensof thousands of people were made homeless. In the followingmonths, most of the homeless found permanent housing, butit will take years to repopulate the ancient masonry cores ofthe settlements in the epicentral area.

Two M> 5 aftershocks followed on 7 April (ML 5.3,Mw 5.6, depth 15 km; epicenter about 10 km southeast ofL’Aquila) and on 9 April (ML 5.1, Mw 5.4, depth 11 km;epicenter near Lake Campotosto, about 15 km northwest of

L’Aquila; Fig. 1). The seismic sequence was still active inOctober 2009 with M> 4 events, despite a nearly typicaldecaying temporal pattern (Chiarabba et al., 2009). It affectedan ∼40-km-long zone, extending in a northwest–southeastdirection with an en echelon dextral step to the north (Fig. 1).The depth distribution of aftershocks suggests that the main-shock activated two southwest-dipping planes without anysignificant listric geometry (Chiarabba et al., 2009). Theone that caused the main event, generating primary surfacerupture with vertical displacement reaching 10–15 cm, corre-sponds to the Paganica fault (Figs. 2 and 3), a mappedbut poorly characterized structure with an approximately100-m-high fault scarp (Fig. 4) cutting Middle to Late Pleis-tocene alluvial fan deposits (Bagnaia et al., 1992; Vezzani andGhisetti, 1998; Boncio, Lavecchia, and Pace, 2004; Agenziaper la Protezione dell'Ambiente ed i servizi Tecnici [APAT],2006; Messina et al., 2009). The second plane, where the 9April aftershock occurred, likely corresponds to the Lagafault (Fig. 3), a major tectonic lineament with a prominent

1507

Bulletin of the Seismological Society of America, Vol. 101, No. 4, pp. 1507–1530, August 2011, doi: 10.1785/0120100140

geomorphic expression (Blumetti et al., 1993; Galadini andGalli, 2003; Boncio, Lavecchia, et al., 2004; Blumetti andGuerrieri, 2007). The seismic sequence along the Laga faultraised strong concerns because of its close proximity to theRio Fucino dam impounding Campotosto Lake. Another seis-mic sequence culminated in an ML 3.9 aftershock (depth11 km) on 25 June, northwest of theCapitignano basin (Figs. 2and 3), where no fault sources are evident (e.g., Blumetti,1995; Galli et al., 2005). The aftershocks associated withthe 7 April event did not define a fault plane responsiblefor such seismicity (Chiarabba et al., 2009) but could fallwithin the northwest-dipping Monte d’Ocre fault system.In Fig. 1, it is notable that the abrupt cutoff of seismicityto the southeast more or less corresponds with the southeast-ern end of the Aterno valley tectonic basin.

Focal mechanisms reported in the Regional CentroidMoment Tensors catalog (see Data and Resources section)clearly define a northeast–southwest horizontal T-axis, inagreement with the tectonic setting of the region, character-ized by active normal faults mostly striking northwest–

southeast. The focal depths were generally less than 10 kmdeep, except for the 7 April shock, which was deeper (about15 km) and characterized by a modest left-lateral component.

For the first time during a major European earthquake,differential Interferometric Synthetic Aperture Radar(DInSAR) images circulated within days of the mainshock,while geologists were in the field mapping surface ruptures,thereby allowing them to utilize fringe geometries to guidetheir search for surface rupture in the field (e.g., imagesprovided by IREA–Consiglio Nazionale delle Ricerche(CNR) and the Istituto Nazionale di Geofisica e Vulcanologia;see Data and Resources section). The DInSAR images re-vealed with growing clarity the amount and distribution ofground deformation, confirming that the Paganica faultwas the culprit for the earthquake (see Atzori et al., 2009;Walters et al., 2009;Guerrieri et al., 2010; Papanikolaou et al.,2010). The coseismic-to-early-postseismic surface deforma-tion had the shape of an asymmetric elliptical bowl with amaximum subsidence close to 30 cm centered between Onnaand Bazzano, about 6 km east–southeast of the instrumental

Figure 1. Location of the 6 April 2009 earthquake (star) and distribution of seismicity between December 2008 and October 2009 (fromthe Italian Seismic Instrumental and parametric Data-basE, ISIDe; see Data and Resources Section). Before the mainshock, most of theforeshocks (largest was ML 4.1 on 30 March) were located in a small zone close to the main epicenter. The color version of this figureis available only in the electronic edition.

1508 E. Vittori et al.

epicenter (Fig. 5). This location corresponds with themacroseismic epicenter; the epicentral intensity was IX onboth the Mercalli–Cancani–Sieberg scale (MCS; Galli,Camassi, et al., 2009) and the European Macroseismic Scale(EMS; Barbano et al., 2009).

Global Positioning System (GPS) data from a densenetwork covering the region showed coseismic horizontalextension of 8–10 cm and subsidence of approximately16 cm (Anzidei et al., 2009; Cheloni et al., 2010) and furtherpostseismic values of 1 and 4.9 cm, respectively, after 60 days

(Cheloni et al., 2010). Modeling of the deformation patternshowed coseismic slip distributed in patches and propagatedfrom northwest to southeast, with maximum values at a depthof 0.6–0.9 m from Synthetic Aperture Radar (SAR) andbody-wave data (Atzori et al., 2009; Walters et al., 2009)and 0.5–0.6 m from GPS data (Anzidei et al., 2009; Cheloniet al., 2010). Estimates of the dip angle of the seismogenicfault vary from 45° to 55°.

Monitoring of local postseismic deformation bymeans ofseveral techniques, such as laser scanning (Wilkinson et al.,

Figure 2. Structural setting of the region hit by the 2009 L’Aquila seismic sequence (modified after Blumetti, Di Filippo, et al., 2002,with permission). The color version of this figure is available only in the electronic edition.

Surface Faulting of the 6 April 2009 Mw 6.3 L’Aquila Earthquake in Central Italy 1509

2010), crackmeters, total station, GPS (Sileo et al., 2009;Degasperi, 2010), DInSAR time series (Lanari et al., 2010),shows a significant afterslip contribution (possibly nearing50% of the coseismic slip) to total slip, still ongoing afterone year and decaying more or less logarithmically (Degas-peri, 2010). Afterslip of the L’Aquila event has been alsoinferred using a laser strain meter system (ε > 600 × 10�9

in the northeast–southwest direction) inside the Gran Sasso

range, 20 km northeast of the epicenter (Amoruso andCrescentini, 2009).

Earthquakes in the range ofMw 6.0–6.5 are hazardous tothe Mediterranean region because (1) they are rather frequentin several countries and (2) the damage expected fromsuch events is quite large, due to the historical heritage ofmasonry buildings making the ancient cores of most townsand to the poor quality of recent reinforced concrete frames

Figure 3. Map of faults capable of surface rupturing known for the study region (from the ITHACA catalog, see Data and Resourcessection) and epicenters of the main historical earthquakes (stars) (Gruppo di Lavoro CPTI, 2004; see Data and Resources section). The A–Bline is the location of the trace of the geological cross section of Fig. 6. ASG, Assergi fault; BAR, Barisciano fault; BAZ, Bazzano fault; CAP,Capitignano fault; CAT, Colle Caticchio fault; CCE, Colle Cerasitto fault; CEN, Colle Enzana fault; CFE, Campo Felice fault; CIM, CampoImperatore fault; CLB, Collebrincioni fault; COC, Colle Cocurello fault; COF, Colle Frolla fault; COP, Colle Praticciolo fault; MAV, MiddleAterno valley fault system; MCS, Monte Castellano fault; MDU, Monti della Duchessa fault; MFS, Monticchio-Fossa-Stiffe fault system;MMA, Monte Macchione fault; MOR, Monte Orsello fault; MRZ, Monte Ruzza fault; MSF, Monte San Franco fault; OPP, Ovindoli-Piani diPezza fault; PAG, Paganica fault; PET, Monte Pettino fault; PIZ, Pizzoli fault; ROC, Roio–Canetre fault; SDE, San Demetrio faults system;SCI, Scindarella fault; SMA, San Martino fault; SSS, Santo Stefano di Sessanio fault system; STB, Stabiata fault; TRS, Tre Selle fault; VAS,Valle degli Asini fault; VDS, Valle del Salto fault. Stars locate the epicenters of the most important historical earthquakes (Gruppo di LavoroCPTI, 2004). The color version of this figure is available only in the electronic edition.


characterizing the incessant urban sprawl of the last fewdecades, often without consideration of natural hazards.

The 6 April 2009 L’Aquila event is the best seismo-logically, geodetically, and geologically documented earth-quake so far in the Mediterranean region. We consider thepattern of normal faulting seen during the 2009 L’Aquilaseismic sequence paradigmatic for moderate earthquakes inthe Apennines of Italy and reasonably for other surroundingregions under active crustal extension.

We will focus here on the primary and secondary surfacefaulting effects (following the definition by Slemmons anddePolo, 1986). To date, the literature includes contrastinginterpretations of the ruptures seen along the Paganica faultand nearby Quaternary normal faults. Consequently, thedistribution and length of the actual primary surface ruptureis debated: from a minimum of 2.5 km to possibly 6 km,according to Blumetti et al. (2009) and EMERGEOWorkingGroup (2009a, 2009b), 19 km according to Galli, Camassi,et al. (2009), and 13 km according to Boncio et al. (2010).

Valensise (2009) maintains that the earthquake originatedalong a blind low-angle normal fault.

Based on the bulk of data illustrated further on, thispaper seeks to reconcile the field, geological, geophysical,and remote-sensing observations of coseismic and postseis-mic slip at the surface in order to: (1) constrain the extent ofthe primary tectonic ground rupturing; (2) give an overviewof the different accounts, drawing conclusions regarding thelessons we can learn from different approaches to fault rup-ture studies; (3) suggest an interpretation of the complexarray of synthetic and antithetic normal faults in the sur-roundings of the main rupture; and (4) discuss the patternof normal faulting seen during the 2009 L’Aquila seismicsequence in terms of the seismic/geological risk of the area.

Tectonic Framework of the Study Region

The L’Aquila seismic sequence occurred inside anorthwest–southeast-trending tectonic depression, theAterno

Figure 4. Three-dimensional view (based on a 20-m digital terrain model) of the L’Aquila region, with the reported net of capable faultsdefining a seismic landscape, according to Blumetti and Guerrieri (2007). (1) The major faults are evidenced by up to a thousand-meter-highfault escarpments and bound first order tectonic blocks. Minor faults within the major blocks, sometimes with an evident listric geometry, canbe ranked in two categories: (2) faults at the base of high fault escarpments, generally representing reactivations of old thrusts and with apossibly gravitational component of the movement and bounding second-order blocks; (3) faults that produce lower fault scarps and boundthird-order blocks. (4) Remnants of low-relief landscape can be used as throw markers. The A–B line is the location of the trace of thegeological cross section. The color version of this figure is available only in the electronic edition.


Figure 5. DInSAR image of the 6 April 2009 earthquake and profiles across the fringes in the fault zone (modified from Guerrieri et al.,2010). MVO, measured vertical offset (field observation); LOS field, predicted offset along the line of sight (calculated fromMVO); LOS dis,measured offset along the line of sight. The focal mechanism is also shown. The white circles are observation points as described in Guerrieriet al. (2010). The color version of this figure is available only in the electronic edition.


valley basin, located between the Gran Sasso and the Montid’Ocre morphostructural units (Bagnaia et al., 1992; Blumet-ti, Di Filippo, et al., 2002; Boncio, Lavecchia, and Pace, 2004;Blumetti and Guerrieri, 2007), within the central segment ofthe Apenninic orogenic belt (Figs. 2 and 3). The tectonichistory of the Apennines, as well as that of the whole centralMediterranean, is driven by a complex interaction of minorplates within the Africa–Eurasia collision (Malinverno andRyan, 1986; Patacca et al., 1990; Gueguen et al., 1998;Doglioni et al., 1999; Piccardi et al., 2011). The presenttectonic structure of the central Apennines is the result ofUpperMiocene–Lower Pliocene northeast-verging thrust tec-tonics (Patacca et al., 1990) overprinted by Late Pliocene toQuaternary northeast–southwest crustal extension, migratingin time and space from west to east, that reached the Abruzziregion 2–3 million years ago and is still active at present, asdemonstrated by seismic (including palaeoseismic) and mor-photectonic evidence (Demangeot, 1965; Blumetti et al.,1993; Barchi et al., 2000; Galadini and Galli, 2000;Pizzi et al., 2002; Boncio, Lavecchia, and Pace, 2004; RobertsandMichetti, 2004; Papanikolaou et al., 2005; Piccardi et al.,2006; Galli et al., 2008; Lavecchia et al., 2010). Geodetic dataprovide velocities (with respect to stable Eurasia) that implyextension rates of 4–5 mm=yr across theApennines (D’Agos-tino et al., 2008; Devoti et al., 2008). Faure Walker et al.(2010) propose a slightly lower extension rate (approximately3 mm=yr), derived by calculating moment tensors from faultslip data, including also the strain from the 2009 L’Aquilaearthquake.

The cumulative effect of block-faulting and fast uplift,initiated approximately 0.8 Ma ago (e.g., Demangeot, 1965;Ambrosetti et al., 1982; Dramis, 1993), gave the AbruzziApennines its typical morphology, characterized by fault-bounded basins and ranges. Some authors (Michetti et al.,2005; Blumetti and Guerrieri, 2007 and references therein)consider the size of the basins and that of the associatedfault-generated mountain fronts as a peculiar attribute, indi-cative of the local seismic potential; this is referred to as seis-mic landscape (Fig. 4). All the major basins (Fucino,L’Aquila, Sulmona) have hosted strong historical and/orpaleoearthquakes.

In the L’Aquila region, surface geology and geophysicaldata reveal a composite structural setting given by severaloverthrust tectonic units belonging to the transitional domainbetween the Lazio–Abruzzi carbonate shelf platform and theUmbria–Marche pelagic basin, dissected by a network ofQuaternary normal faults, in places located close to theuppermost traces of older thrust planes (Vezzani and Ghisetti,1998; APAT, 2006). Seismic and stratigraphic-morphologicalevidence suggest ongoing activity along several of thesefaults (Fig. 3; e.g., Bagnaia et al., 1992; Blumetti, 1995;Piccardi et al., 1997; Moro et al., 2002; Boncio, Lavecchia,and Pace, 2004; Roberts and Michetti, 2004; Papanikolaouet al., 2005; Galli et al., 2008).

We synthesize the Quaternary evolution of the localarea around L’Aquila in two phases. During the Lower

Pleistocene, lacustrine environments dominated the area ofthe present Aterno valley. At that time, though normal faultswere already shaping a number of lacustrine basins, the land-scape still had a low relief and in some zones, for example inthe Campotosto area, wide pediments formed due to arealerosion (Demangeot, 1965). Remnants of these pedimentsare found at different elevations in the present landscape,which is deeply dissected by linear erosion, following thedramatic increase of the uplift rate and faults activity sincethe end of the Lower Pleistocene (Demangeot, 1965; Ambro-setti et al., 1982; D’Agostino et al., 2001).

Similar to the displacement of the Monte Marine summi-tal paleosurface (Blumetti and Guerrieri, 2007), we interpretthat the middle Aterno valley surface [about 600 m above sealevel (m.a.s.l.)] was downthrown by the Paganica–SanDemetrio normal fault (Bagnaia et al., 1992) with respectto the Anzano Plateau summit paleosurface (1500 m.a.s.l.)at the southern edge of the Gran Sasso block (Figs. 2–4).The latter, reaching the highest elevation in the Apennines(close to 3000 m), is dissected by a set of west-northwest–east-southeast-trending south-dipping normal faults (e.g.,the Assergi and Campo Imperatore faults) that have a listricgeometry, possibly representing reactivations of old thrusts atdepth (D’Agostino et al., 1997). Together with other second-ary faults, they are contained in a first-order tectonic block(here named the Gran Sasso morphotectonic unit) and joinat depth the Paganica—SanDemetrio high-angle normal fault(Blumetti et al., 2010). In this view, the Paganica—SanDemetrio is the master fault of the whole block. Becauseof the great difference in elevation, gravity-drivenmovementslikely contributed to the total slip observed on the higherelevation listric faults (Nijman, 1971; Bagnaia et al., 1992;Blumetti, 1995; Dramis and Blumetti, 2005).

At the southwestern border of the middle Aterno valley(Figs. 2 and 3), the Bazzano, Fossa, and Villa Sant’Angeloantithetic faults bound the northern edge of the Monti di Ocrestructural unit, crosscut by a network of minor faults display-ing an en echelon pattern (Roio–Canetre, Colle Cerasitto,Campo Felice, and Monte Orsello faults).

Based on the state-of-the-art seismotectonic and paleo-seismic research, the capable faults located around the epi-central area [from the ITalian Hazard from Capable faults(ITHACA) database; Vittori, 2000] are shown in Fig. 3. Ageological cross section (Fig. 6) shows that most of theQuaternary tectonic deformation in the earthquake epicentralarea is accommodated by the Paganica fault segment, withthe Bazzano–Fossa fault acting as an antithetic structure.The synthetic Roio–Canetre fault, which displaces MiddlePleistocene alluvial deposits (APAT, 2006), is also a sec-ond-order fault within the Monti di Ocre structural unit.

The lack of a clear fault-generated mountain frontrelated to of the Paganica fault segment is due to the presenceof a paleodrainage in the footwall since at least the end ofLower Pleistocene (Paleo-Raiale, sensu Messina et al.,2009). Relict forms of this paleolandscape and differentorders of fluvial deposits terraced by the progressive activity


of the Paganica fault are still preserved in the footwall.Across the Paganica fault, terraced deposits displaced byapproximately 150 m contain tephra layers from eruptionsof the Latium volcanic districts that occurred between 560and 360 ka (Fig. 6). Constrained by these data, the Paganicafault long-term slip rate is approximately 0:4 mm=yr (Mes-sina et al., 2009). This is comparable with the 0:3 mm=yrestimate from ground-penetrating radar (GPR) surveys(Roberts et al., 2010).

Historical Seismicity and Paleoseismicity

According to available catalogs (Gruppo di LavoroCPTI, 2004; Guidoboni et al., 2007), the region experiencedseveral moderate-to-strong earthquakes (Fig. 3) in historicaltimes. Two events had their epicenter very close to that of2009: the 1461 A.D. (intensity X MCS) and the 1762 A.D.(intensity IX MCS) earthquakes (Guidoboni, 2009; Tertullia-ni et al., 2009). Modest documentation survived concerningthe 1461 sequence, with a peak intensity of X MCS at Onna.The matching epicentral areas make the 1461 event a candi-date twin of the 2009 earthquake. The area with highestdamage in the 1762 event was a few kilometers to the south-east of the 2009 event. The peak intensity (IX–X MCS atCastelnuovo) was lower than for the 1461 event, and itsepicentral area was rather small, affecting L’Aquila withan intensity VII MCS. An intensity IX–X MCS event tookplace in 1349 A.D., with a calculated epicenter approximately20 km to the south, but documentation may be too scarce todefine its correct location with some reliability (Boschi et al.,1995). The strongest and best-documented nearby event isthe seismic sequence of 1703, characterized by three main-shocks that shifted in a few days along a north-northwest–south-southeast alignment (Blumetti, 1995; Boschi et al.,1997; Cello et al., 1998; Moro et al., 2002; Galli et al., 2005;Guidoboni, 2009). The first shock, the so-called Norciaevent, took place on 14 January 1703 (intensity XI MCS)and completely destroyed many localities in southernUmbria. The second event, on 16 January 1703 (intensityVIII MCS), hit a small area including the towns of Monter-eale, Cittareale, Accumuli, and Amatrice. The third event, on

2 February 1703 (intensity X MCS), destroyed the city ofL’Aquila, causing 2500 casualties (Baratta, 1901; Boschiet al., 1997). The epicenter for the 2 February earthquakeis estimated to have been a few kilometers northwest ofL’Aquila, along the Monte Marine fault, where it producedsurface faulting for a length of about 20 km (Blumetti, 1995;Moro et al., 2002).

Several active tectonics and paleoseismological studiescontributed in the last decades to define the late Holoceneactivity of a number of active faults in the central Apenninesand to estimate short-term slip rates, minimum thresholds ofexpected magnitude, and recurrence intervals between majorevents (Blumetti, 1995; Giraudi and Frezzotti, 1995;Michetti et al., 1996; Pantosti et al., 1996; Galadini andGalli, 2000; Galli et al., 2002; Moro et al., 2002; Serva et al.,2002; Galli et al., 2008). Estimated Late Pleistoceneminimum slip rates for the Monte Marine fault are 0:25–0:43 mm=yr (Galadini and Galli, 2000), whereas onlylong-term slip rates are available for the Paganica fault(approximately 0:4 mm=yr; Messina et al., 2009) and themiddle Aterno valley fault system (0:33–0:43 mm=yr; Ber-tini and Bosi, 1993; Galadini and Galli, 2000). As mentionedpreviously in this paper, the Assergi and Campo Imperatorefaults have rather high slip rates of about 1 mm=yr (Giraudiand Frezzotti, 1995; Galli et al., 2002).

Coseismic Ruptures

The very day of the mainshock, we begun surveys acrossthe affected area, looking for evidence of geological effects(Fig. 7), especially fault reactivation, whose first hint wasgiven by the rupture of the Gran Sasso aqueduct acrossthe Paganica fault (Figs. 8–10). The pipeline is known tohave ruptured during the mainshock because local peoplereported to have heard water escaping from the pipe imme-diately after they ran out of their dwellings following thequake. This fault zone already has been sketched in severalpapers (Bagnaia et al., 1992; Vezzani and Ghisetti, 1998;Boncio, Lavecchia, and Pace, 2004; Pace et al., 2006) butis mapped in detail in its correct location only in the officialmap of the Cartografia Geologica CARG project (APAT,

Figure 6. Geological cross section across the middle Aterno valley basin, intersecting the Roio–Canetre, Bazzano, Colle Caticchio, andPaganica faults (map trace in Fig. 3). The color version of this figure is available only in the electronic edition.


Figure 7. (a) Distribution of all earthquake environmental effects mapped after the 6 April 2009 earthquake. (b) Enlargement of epi-central area (corresponding to the box in Fig. 7a), showing the distribution of all suspected cases of primary (circles) and sympathetic/secondary (squares) coseismic surface ruptures along the known capable faults of the April 2009 seismic sequence region. The color versionof this figure is available only in the electronic edition.


2006). Bagnaia et al. (1992) documented activity of the faultthrough the last glacial maximum, and several later papersdeclared the fault active (e.g., Boncio, Lavecchia, and Pace,2004; Pace et al., 2006). The Quaternary fault escarpment atPaganica, which cuts alluvial fan deposits dated at theuppermost part of the Middle Pleistocene (Messina et al.,2009), has a more subdued geomorphic expression withrespect to many limestone fault scarps of the region. Theimmediate search along the Paganica fault, prompted byits close location with respect to the hypocenter of the main-shock, revealed evidence of surface rupture (Fig. 9). Namely,the surface expression of the fault appeared as a narrow lineof ground cracks, sometimes showing a modest verticaloffset not exceeding 10 cm, that is more or less continuousalong a distance of 2.6 km, corresponding to the villages ofTempera and Paganica; fractures were rather sporadic north-west and southeast of it (Blumetti et al., 2009; EMERGEOWorking Group, 2009a, 2009b; Falcucci et al., 2009; Fara-bollini et al., 2009; Galli, Camassi, et al., 2009; Boncioet al., 2010).

A comprehensive mapping of these cracks and second-ary environmental effects was carried out (Fig. 7a). Theresults are illustrated in detail and discussed with respect

to the application of the Environmental Seismic Intensityscale (Michetti et al., 2007) and in Blumetti et al. (2009).For those fractures we could not refer with sufficient confi-dence to surface faulting, we have retained their classifica-tion among secondary effects.

Ruptures along the Paganica Fault

A set of nearly continuous and well-aligned groundruptures was found along the Paganica fault (Figs. 3, 6, 7,and 9). The fracture system was located in the middle (some-times close to the foot) of the well-expressed fault scarp. Inthe village of Paganica, the ruptures caused significantdamage to buildings and infrastructure sitting on the fault.The rupture zone, trending between 120° N and 140° N, wasconfidently traced for a length of about 2.6 km, reachinga vertical offset in excess of 10 cm in a few sites (seeFigs. 10–12). Although we also traced the rupture zone onsoil (which was quite stiff because of the dry period), it wasbetter observed on paved/concrete surfaces and often dirtroads and as cracks on buildings and rigid boundary fences.In some places, the rupture was distributed over a numberof parallel cracks spread across a few meters to a few tensof meters, without a main rupture trace. In general, most

Figure 8. (a) Landscape view of the Aterno valley looking east, with arrows showing the Paganica fault (left), the Monte Caticchio fault(center), and the Bazzano fault (right). (b) Landscape view of the Aterno valley between San Gregorio, Onna, and the industrial area ofBazzano; the Monti D’Ocre are in the background. (c) Landscape view of the epicentral area (foreground) looking toward the Paganica–SanDemetrio fault escarpment (arrows). The color version of this figure is available only in the electronic edition.


of the deformation was seen as a single fracture or a narrow,meter-wide fracture zone.

Moving from west-northwest to east-southeast, the firstunequivocal sign of surface faulting was seen at Tempera (atLa Cartiera (paper-mill), Via Capo Vera—site 01 in Fig. 9).Here, five larger fractures and several minor ones occurred ina section of about 60 m, cutting across a local asphalt road;three of these showed an up to 2 cm width and a < 1 cmthrow, while most of the others were simple hairline cracks.In the soil several tens of meters east of the road, inside theprivate garden of a restaurant (site 02 in Fig. 9), the defor-mation took the form of an up to 10-cm-wide fracture, with athrow of 7–8 cm and a length of about 6–7 meters (Fig. 11).

Moving east-southeast, the fracture zone could be seenagain with some continuity (many cracks were 5–20 meterslong) in Santo Rivoru of Paganica (site 03 in Fig. 9), cuttingsecondary dirt roads, pavements, boundary walls, and farmedground, with cracks showing 1–2 cm opening and offset.Further to the east-southeast, the rupture started to signifi-

cantly affect the man-made environment, damaging houses,streets, and utilities (water and gas pipelines, etc.) recentlybuilt across the fault.

Just west-northwest of Santa Croce street (San Gregoriolocality, site 04, Fig. 9) the water main (diameter 70 cm) ofthe Gran Sasso aqueduct, which feeds L’Aquila (mean flowrate 0:5 cubicm=s, pressure reaching 40 bars), was severelydamaged. The pipe failed, and the high pressure outflowproduced gully erosion and a mud flow that coursed throughthe streets and houses downslope (Fig. 10). The deep trenchand following excavation to repair the rupture provided anextraordinary exposure of sediments displaced by a systemof fault splays and unequivocal paleoseismological evidenceof Holocene coseismic offset significantly larger than that ofthe 2009 event. So far, dating of faulted sediments with LatePleistocene–Holocene ages are presented by Galli, Giaccio,et al. (2009), Cinti et al. (2009), Boncio et al. (2010), andPantosti et al. (2010). We have obtained two radiocarbonages: (1) a faulted dark-colored, volcaniclastic-rich paleosol

Figure 9. Distribution of coseismic surface faulting along the Paganica fault. Numbers in boxes refer to sites cited in the text and inFigures 10–12. W1 and W2 are sites of hydrological anomalies along the fault zone. The color version of this figure is available only in theelectronic edition.


(sample ACQ1, Fig. 10c,d) yielded an age of 26; 388�200 yr B:P: (calibrated 31; 651� 260 yr B:P:), which ispuzzling because the clastic body that includes this paleosolis attributed to the Middle Pleistocene, based on tephracorrelation (e.g., Falcucci et al., 2009; Boncio et al.,2010); and (2) brown colluvium on the hanging wallof the fault ruptured on 6 April 2009 (sample ACQ2,

Fig. 10c) yielded an age of 26; 008� 200 yr B:P: (calibrated31; 240� 256 yr B:P:).

Three GPR surveys in the vicinity of the ruptured pipe(Roberts et al., 2010) revealed layered stratigraphy offsetacross a set of en echelon faults that resemble those exposedin the gully eroded by water escaping from the broken aque-duct. The cumulative offsets on the base of the Holocene,

Figure 10. Coseismic faulting at Paganica in the area of the Gran Sasso aqueduct. (a) Fault scarp across the broken aqueduct (center);arrows mark the trace of the coseismic rupture (point 4a in Fig. 9). (b) Oblique aerial view taken in 2008 of the Gran Sasso aqueduct area and(c) same area of (b) just after the earthquake (see Data and Resources section). The erosion determined by the water main rupture andconsequent downslope debris flow are evident in the center of the photograph in (c). (d) Detail of the aqueduct trench (southeastern wall),showing a displaced dark brown paleosol. (e) Fault rupture across the tarmac street just east of the aqueduct (point 4b in Fig. 9). (f–h) Thelargest observed coseismic displacements (10–15 cm) were seen at several spots east of the aqueduct (respectively, points 5, 4a, and 4c inFig. 9); the latter point is inside a house resting above the fault. (i) One of the crackmeters/strainmeters deployed by the Trento GeologicalSurvey (Degasperi, 2010) to monitor the postseismic deformation (same location as seen in h). The color version of this figure is availableonly in the electronic edition.


interpreted from the GPR data, confirm the observations madein the gully exposure that Holocene offsets are a maximum of3–4 m. Within tens of meters east and east-southeast of theruptured water pipe, major damage occurred to the recentlybuilt houses resting on the fault, particularly open crackswith a vertical offset up to 10 cm, affecting floors, walls, andconcrete frames.

Further to the east-southeast, the deformation belt(approximately 15 m wide) was characterized by en echelonfractures.Where the upper crack cut the floor of a small quarrybehind a house (Fig. 10f; point 05 in Fig. 9), the largest verticalcoseismic offset of the fault was 10 cm, increasing to 15 cm inthe following months (possibly enhanced by slope instabil-ity). On the concrete road nearby (point 5 in Fig. 9), a GPRprofile showed offset of layered stratigraphy down to depthsof about 10 m (Roberts et al., 2010). Offsets imaged in thesubsurface were located precisely below locations whereruptures crossed the concrete road.

Two parallel branches (20 m apart) of the fault cut theroad to Camarda (SR 17 bis/A—site 06 in Fig. 9) and thebridge nearby, across the Raiale creek. Moving southeast,more or less continuously, this rupture belt could be tracedagain in the upper (northeast) edge of the Paganica villageat the base of the Middle Pleistocene scarp, still affectingartificial surfaces, farmed fields, and a number of newconstructions.

Just east-southeast of the bridge, aboveVia delCaldarello(site 07 in Fig. 9), the rupture zone was comprised of twosubparallel main traces approximately 20 meters apart. Theupper rupture was better manifested and continuous, consist-ing of two subparallel slightly curved branches, locallyshowing an en echelon arrangement of cracks that are clearlyvisible on an asphalt pavement for approximately 12 m(Fig. 12b), one (on the left in the figure) dipping south (down-slope) with an opening of approximately 2–3 cm, offset of afew millimeters; the other one counterdipping and opened up

Figure 11. Fault rupture at Tempera (point 01 in Fig. 9). (a) Photo taken on 8 April and (b) photo taken on 17 April. In (a) the separationwas mostly vertical (throw about 1 cm) with minor horizontal aperture; while in (b), a significant opening in excess of 3 cm is evident. This isonly one of a system of at least ten fractures that occurred over a distance of 60 m. (c,d) 100 m southeast of the point in (a and b); in the pointin (c and d), which is the same as point 02 in Fig. 9, the rupture appeared as a single wide crack in soil, with a vertical throw of approximately8 cm. The color version of this figure is available only in the electronic edition.


to 4 cm with similar offset. The main rupture could be tracedeastward, reaching amaximum offset of 7 cm and openings of4–5 cm, cutting gardens and small vineyards, dirt and pavedroads, pavements, fence walls, and recent construction (site 8in Fig. 9). East of via delle Rocce, buildings are sparse and thefault crossed farmed fields; however, two very recent housecompounds rest on the fault (9a and 9b in Fig. 9) and weredamaged by its activation. Openings and offsets were gener-ally modest (a few centimeters at most) but well evident (sites9a and 9b in Fig. 9).

The easternmost place where the fault could be traced isroute SP103 to Pescomaggiore. Here the asphalt surface wasobliquely crossed by a cracked undulation over a bandapproximately 2 m wide, with a clearly visible smoothed stepthat can be felt by vehicles and reached a height of approxi-

mately 10 cm in the following days (site 10 in Fig. 9). About460 m to the east along the same road, a parallel rupture dis-placed the road floor, the concrete retaining wall uphill, andalso the farmed field to the east, here with a partly curvedshape, thus suggesting a land slip (site 11 in Fig. 9).

In the eastern area of Paganica, two additional, nearlycontinuous, fracture lines were mapped south of the mainline previously described here, located 120 and 250 m fromit, respectively (Fig. 9). The intermediate rupture was similarto the main one, cutting fields, walls, and pavements for amapped length of nearly 600 m; its likely westward continua-tion could not be verified because it continued into the off-limit area of the ruined village. The southernmost crack alsowas mapped starting from the border of the restricted area.Its mapped length (115 m) and surface signature (a thin,

Figure 12. Coseismic faulting along the Paganica fault. (a) Faulting across the road to Camarda, where it is monitored with a buriedstrainmeter (point 06 in Fig. 9). (b) Fractures in a tarmac surface (point 07 in Fig. 9); (c) en echelon cracks in the same spot as (b). (d) Surfacefaulting in soil (point 8 in Fig. 9). The color version of this figure is available only in the electronic edition.


approximately 1-cm-wide crack without vertical displace-ment) were rather modest compared to the other two cracks,and no significant damage appeared to be associated with it.

In the frame of a collaboration among several academicand research institutes (Istituto Superiore per la Protezione ela Ricerca Ambientale, Provincia Autonoma di TrentoGeological Survey, Università dell’Insubria, CNR, BirkbeckCollege University of London, and Durham, Leeds, andEdinburgh Universities), high precision instruments moni-tored postseismic movements of the Paganica ruptures (e.g.,Light Detection and Ranging, total station, GPS) and docu-mented a remarkable postseismic evolution of the Paganicaruptures in terms of increasing offsets, lengths, and widthswith time (Sileo et al., 2009; Degasperi, 2010, Wilkinsonet al., 2010). The formation of new fractures even severaldays after the mainshock was noted. The throw increasedrapidly in the first days, 2–3 cm in the first week or so, con-tinuing to grow in the following weeks and months (2.5 cmadditional throw), reaching a maximum of approximately15 cm from the 10 cm of coseismic slip, seen just east ofthe damaged aqueduct and about 350 m southeast from it(site 05 in Fig. 9; Degasperi, 2010; Wilkinson et al., 2010).

Field observations revealed other cracks (with or with-out offset) to the northwest and southeast of the main rupture,often in correspondence with fault planes in places alignedwith the Paganica ground rupture zone (e.g., EMERGEOWorking Group, 2009a, 2009b; Falcucci et al., 2009; Galli,Camassi, et al., 2009; Boncio et al., 2010). Some authorssuggest these cracks are the extension of the fault rupture,despite their more sporadic nature and lack of continuity withthe Paganica rupture (Fig. 7b).

Galli, Camassi, et al. (2009) mapped fractures as farwest as northwest of Collebrincioni along and inside thehanging wall of the Colle Praticciolo fault. EMERGEOWorking Group (2009b) recognized these ruptures only inthe easternmost part of this fault; they also mapped otherlocal ground ruptures along the northeast-dipping Valledel Macchione fault. A reactivation of the Monte Enzanofault with an offset reaching 6 cm at the contact fault plane-debris deposits was seen (EMERGEO Working Group2009a; Galli, Camassi, et al., 2009; Boncio et al., 2010).A thin rectilinear fracture trending 140° N crossed a dirtroad east of the San Biagio cemetery (point 113 in Fig. 7b).Modest (≤1-cm-wide) fractures trending 100°–170° N werereported (EMERGEOWorking Group, 2009a; Falcucci et al.,2009; Farabollini et al., 2009) near and under the viaductVigne Basse of the Motorway A24. Boncio et al. (2010)pointed out localized reactivations of the Monte Castellano–Monte Stabiata fault as free faces 2–6 cm high at or near thecontact fault plane-colluvium (points F1 and F2 in Fig. 7a).

At the opposite southeastern tip of the Paganica fault,differing opinions exist about the nature of ruptures proposedby several authors. Coseismic fractures opened in farmedfields northwest of San Gregorio hill, approximately at thenorthwestern tip of Valle degli Asini, southwest of ColleSan Vittorino (sites 166 and 167 in Fig. 7b), with a length

of some hundred meters and direction 140°–160° N. Accord-ing to the farmer, the day after the main quake, one couldobserve a longer fissure in the ground, propagating acrossSan Gregorio hill. Falcucci et al. (2009) and Boncio et al.(2010) interpret these ruptures as a reactivation of an enechelon southeastern component of the Paganica fault sensustricto, bordering the northeastern side of Valle degli Asini.These same authors have also noted some ground cracksaffecting roads, paved surfaces, and walls at San Gregorio(points F3 and F4 in Fig. 7a), which should still be consid-ered part of the fault reactivation zone.

We interpret as secondary phenomena some thin frac-tures striking 130° N on streets and walls at the foot of thefault scarp inside the urban area of San Demetrio ne’ Vestini(points 198 and 199 in Fig. 7b). Conversely, Galli, Camassi,et al. (2009) interpret the latter and a set of ground fissurescutting farmed land in the hanging wall of the San Demetriofault as evidence of fault activation. In this way, they estimatethe overall length of surface faulting at 19 km, from the set ofruptures observed by them north of Collebrincioni (along theColle Praticciolo fault) to those in San Demetrio ne’ Vestini.Finally, Boncio et al. (2010) estimated the length of surfacerupture at approximately 13 km from the Stabiata fault to SanGregorio.

Coseismic Surface Ruptures along Other Faults

The Pettino fault marks the base of a prominent fault es-carpment bordering the northern side of the L’Aquilabasin, displaces Holocene–latest Pleistocene landforms anddeposits, and is considered capable of producing M >6–6:5earthquakes (Blumetti, 1995; Moro et al., 2002; Boncio,Lavecchia, and Pace, 2004; Blumetti and Guerrieri, 2007).Blumetti et al. (2009), EMERGEO Working Group (2009a,2009b), and Farabollini et al. (2009) observed only localground ruptures along the Pettino fault, some cracks tensof meters long with offsets up to 20 cm (points 176 and177 on Fig. 7b), which is hardly interpretable as coseismicreactivation. Along the southeastern portion of the fault, CaseCastelvecchio (point F5 in Fig. 7b), Farabollini et al. (2009)and EMERGEO Working Group (2009b) describe severalfractures parallel to the fault on a paved road, locally witha throw of a few centimeters. According to the same authors,south of Collebrincioni along the route SS70 to L’Aquila, aminor fault (trending 110° N, interpreted as a secondary faultin the footwall of the parallel Pettino structure) showed 4 cmof offset at the contact fault mirror-colluvium. No evidence offracturing was seen either in the urban area of L’Aquila oralong the northwestern section of the fault.

Across the asphalt road above the northwestern wall ofthe Cava Vaccarelli, eight cracks were mapped over a dis-tance of about 50 m, with openings up to 2 cm (point189 in Fig. 7b). More cracks were visible a few tens of metersaway southwest on the same road. This system of fractures,striking approximately 130° N, stood right above the evidentmapped normal fault of similar strike (dipping southwest)


that offsets a Mesozoic limestone exposed in the nearlyvertical wall of the quarry (approximately 30–40 m high).Along strike, similar fractures cut the road San Giacomo–Aragno, which runs on the opposite side of the quarry (point64 in Fig. 7b). This rupture zone is close to a nearly east–west south-dipping fault (Colle Frolla fault, COF in Fig. 3)mapped by Vezzani and Ghisetti (1998), which may correlateto a weakly-expressed linear anomaly in the fringe distribu-tion of DInSAR images (Guerrieri et al., 2010).

A free face was found along the 125° N-trending Canetrefault, at a short distance from Roio (Fig. 3). A nearly constantoffset of 1–3 cm was seen for at least 1 km, not only alongdebris-rock contacts but also across a rock-to-rock contact(point 70 in Fig. 7b; Fig. 13).

Along the trace of mapped faults of the Campo Impera-tore active fault system (Fig. 3), discontinuous northwest–southeast-trending cracks were seen on 10–12 April 2009,affecting a deep snow cover over a distance of at least somehundreds of meters. Interestingly, the cracks showed the samestrike and sense of downthrow (0.5–1.0 cm) as the faultsmapped by Galli et al. (2002). In one location, the groundappeared to be offset vertically by approximately 30 cmwherea small hole in the snow (5 m ×5m area) allowed observationof the ground on a steep slope. However, when revisitedin July 2009 after the snow had melted, no signs of a contin-uous ground rupture were found, the 30 cm offset clearlybelonging to a small (approximately 30-m-long landslidescar). Interpretation of the snow fractures is difficult, but herea secondary origin is more likely because of the amount ofdisplacement and the lack of any other evidence of activation(e.g., significant foreshock and aftershock activity), attributa-ble to this prominent south-dipping fault. It may be thatshaking caused compaction of hanging-wall sediments tothese geological faults, causing an offset of the snow.

Along the northeastern Monticchio–Fossa–Stiffe sectionof the Monti d’Ocre border fault, several parallel fractures, afew meters long and trending 110°–120° N, were mapped8–12 m apart from each other, cutting across Via delle Chiusenorthwest of Fossa (site 145 in Fig. 7b). No appreciable throwwas evident, and no evidence of them was seen in the fieldsbeside the road. These fractures are close to one of the veryfew examples of liquefaction caused by this earthquake.

EMERGEOWorking Group (2009a) mapped open frac-tures (up to 1 cm) along or near the fresh-looking scarp of theMonticchio–Fossa fault, especially near Fossa, extendingfor at least 300 m. According to them, a reactivation of theborder fault is the most likely cause of the coseismic effectsobserved along this fault zone. However, the origin of manycracks also could be linked to secondary causes (e.g., failuresof the road embankment, as observed in the paved road nearTussillo and the cemetery of Casentino) very close to thesame fault zone. Interpretation of DInSAR data (Fig. 5;Guerrieri et al., 2010) shows a linear anomaly in the fringescorresponding to this fault line; however, the resolution is toolow to confirm a fault deformation. As a result, the evidencefor this reactivation is not conclusive.

A system of at least eight parallel, 4–5-m-long, hair-thinfractures, trending approximately 100° N, were mapped on 8April, cutting through a dirt road and artificial fill insidethe Ciuffini quarry (near Tempera; point 77 in Fig. 7b).Next to these fractures, a wide limestone slickenside(310° N, dip 65°), uncovered by quarry excavation, showedvolcanic soil entrapped within it, suggesting activity in thelate Quaternary. Thirteen days later, two more small fractureswith the same trend appeared close to the ground cracksdescribed previously (point 115 in Fig. 7b), which, in themeanwhile, had become wider (up to 1 cm) and longer(5–10 m) than before. These cracks and the fault planeare aligned with the northwestern tip of the Monte Caticchiofault, are northwest-dipping, and are located approximately350 m to the southeast. At this tip, a wide crack (clearly visi-ble on the 15-m-high artificial wall of the borrow pit; point160 in Fig. 7b) opened in the Mesozoic limestone, close andparallel to the fault scarp (strike 310° N, dip 65°), as an effectof the earthquake.

Along the Bazzano fault, which is a prominentnorthwest–southeast-trending normal fault antithetic to thePaganica fault at 2.8 km distance (Figs. 3 and 7b), a discon-tinuous free face was seen, marked by a white strip andlocally by the displacement of moss attached to the slicken-side surface, which is up to several meters high along thisfault (Fig. 13). The free face was followed discontinuouslyfor several hundred meters, showing up to 2–5 cm of throw.Rather large but localized displacements, up to 30 cm, werealso reported (EMERGEO Working Group, 2009a, 2009b;Falcucci et al., 2009). Moreover, along the access road toBazzano (site 195 in Fig. 7b) a 10-m-long fracture trending320° N appeared, cutting the asphalt and the ground with anopening of up to 4 cm and a throw of approximately 1 cm.This might be interpreted as another sign of fault reactiva-tion, being located right in line with the mobilized faultmirror nearby. However, taking into account the local steepmorphology and the discontinuous nature of the white stripeexposed by slip, a lateral spread would also be a reasonableexplanation. No appreciable deformation is visible onDInSAR images (Fig. 5).

Some fractures (strike 130°–160° N; width 3–5 cm, novertical offset; length about 20–30 m) appeared close toOnna, in a flat area 200 m northeast of route SS17 (points103–107 in Fig. 7b). On line with these structures, more frac-tures with the same trend were observed on the floor of aborrow pit at the northeastern border of the Bazzano indus-trial area (points 92 and 94 in Fig. 7b). This alignment ofcracks, cutting the outer deposits of the Paganica fan, donot correspond to mapped faults but do appear in line withthe Monte Caticchio normal fault. Conversely, Boncio et al.(2010) consider these fractures part of a system that theyfollowed with some continuity for a length of approximately4 km from San Gregorio to a few hundred meters east of thesouthern tip of the Monte Caticchio hill (Fig. 7b). Theseauthors interpret such fractures as the reactivation of a south-west-dipping normal fault, named the San Gregorio fault,


Figure 13. (a) Ground rupture along the Bazzano fault zone (site 6 in Fig. 7b). The faulted northeastern slope of Mt. Bazzano is visible inthe background. (b) Limestone slickenside of the Bazzano fault (point 73 in Fig. 7b). (c) Detail of the fault mirror in (b), showing thesupposed centimetric coseismic slip. (d) Roio–Canetre fault scarp looking southeast (site 70 in Fig. 7b). (e) Detail of the fault mirror;the finger points to the centimetric coseismic offset. The color version of this figure is available only in the electronic edition.


buried under the Late Pleistocene Paganica alluvial fan andrevealed by geophysics and borehole stratigraphy.

Secondary slip along the Bazzano and Monte Caticchiofaults would be expected, accommodating the slip of thePaganica fault, which they probably meet at shallow depths:respectively 2000–2400 and 1000–1500 m (Fig. 6). Beingthe trace of the buried synthetic San Gregorio fault only400 m northeast of the Caticchio fault, its relationship withthese antithetic faults needs to be clarified.

Discussion

The ruptures along the Paganica fault are interpreted asevidence of coseismic surface faulting. The direct link withthe seismogenic source is suggested by the seismologicaldata (distribution of aftershocks, size of the rupture, focalmechanisms) and the coseismic field of deformation result-ing from the comparison of pre- and post-event SAR images(Atzori et al., 2009; Walters et al., 2009; Papanikolau et al.,2010; Guerrieri et al., 2010) and GPS measurements (Anzideiet al., 2009; Cheloni et al., 2010). There is little doubt thatthe Paganica fault (Figs. 1, 5, and 7) was the causative sourceof this earthquake, a conclusion reached by all of the geologygroups working on this fault (e.g., EMERGEO WorkingGroup, 2009a, 2000b; Galli, Camassi, et al., 2009; Falcucciet al., 2009; Boncio et al., 2010).

Estimated surface rupture length (SRL) ranges between2.6 and 19 km, depending on the interpretation given by thedifferent authors to the cracks along strike of the main rup-ture zone; we think the difference in values provided by dif-ferent research groups is interesting and that discussion ofthe range of values provides important new insights intothe variables that need to be considered when assessing anearthquake rupture. We provide a conservative estimate of2.6 km for SRL because this was the extent of continuoussurface faulting as opposed to ground cracks. A similar viewis shared with EMERGEO Working Group (2009b). Othergroups include discontinuous faulting and ground cracks,such as the overall length of approximately 13 km providedby Boncio et al. (2010) from the Stabiata to the San Gregoriofaults, or 19 km by Galli, Camassi, et al. (2009), who inter-preted ground cracks along the fault scarps at San Demetrioas coseismic faulting (Fig. 14). Of interest are the questionsof how continuous surface faulting and ground cracks relateto each other and how both relate to inferred displacement atdepth, interpreted through modeling of off-fault surfacedisplacements measured with DInSAR. In Figure 5, wereproduce the fringe data and the sections published in Guer-rieri et al. (2010), where the deformation field depicted byDInSAR images is suggestive of a sharp cut only in thecrosscut profiles across the village of Paganica and possiblyto the northwest (profiles 2–5), giving a surface rupture ofabout 6 km at most.

The maximum coseismic surface displacement (MD) iswell constrained to 10–15 cm. Although fault slip at thenorthwestern and southeastern tips of the Paganica fault

surface rupture is clearly indicated by aftershock distribution,ground deformation, and modeling of rupture at depth fromseismological, SAR, and GPS data (Anzidei et al., 2009;Atzori et al., 2009; Cheloni et al., 2010; Walters et al., 2009;Papanikolaou et al., 2010; Guerrieri et al., 2010), surfacedisplacements are not clear on the interferogram. Thus,whether the rupture at depth propagated to the surface alongits entire length (giving the larger SRL values) or along onlypart of its length (giving our preferred value of 2.6 km orsomething between this value and 19 km) is a key questionin SRL–magnitude relationships that has received little atten-tion until now. It is very likely that, with a careful searchaway from the main rupture tips, more or less scatteredground cracks, like those reported for the 2009 event, couldhave been noticed for most of the past earthquakes compos-ing SRL datasets, such as that of Wells and Coppersmith(1994). However, it is very unlikely that such cracks wereinterpreted in a univocal manner, if seen at all, and have beenaccounted for together with the most evident ruptures. So,apart from the correct genetic interpretation to be given,we retain that, to be consistent with the past, we should avoidincluding in the size of the SRL the ground cracks that are notobviously continuing the main rupture and that lack a clearoffset.

It has been inferred for a number of previous earth-quakes that the surface rupture and slip are only a fractionof the total rupture (Wells and Coppersmith 1994). Herewe point out that the actual length we measure at the surfaceis constrained by the shape of displacement contours near theupper tip of the rupture. If different earthquakes of the samemagnitude have different-shaped displacement contours neartheir upper tips, then their surface rupture lengths, subsurfacerupture lengths, and surface slip may differ, consistent withthe scatter in surface rupture lengths versus subsurface rup-ture length in empirical datasets (see Wells and Coppersmith1994, their fig. 2). The uncertainty regarding the exact shapeof the displacement contours is evident in comparisons ofslip-distributions derived from inversions of ground defor-mation data for the same earthquake; for example, comparethe differences between slip-distributions on the 2009L’Aquila earthquake derived by Atzori et al. 2009 andWalters et al. 2009. We consider the most likely explanationof the surface cracks observed away from the Paganicarupture and on line with it to be the surface accommodationof slip at depth, tapering out away from the hypocenter.Thus, if uncertainty exists regarding the shape of the dis-placement contours between studies of the same earthquake,it is clear that this uncertainty will propagate into errors andhence more scattering in empirical rupture length datacatalogs (Wells and Coppersmith 1994, their fig. 2). If thisis the case, the MD may be a better guide than SRL topaleoearthquake magnitude, given the current SRL–MDdatasets. Despite all this uncertainty, and considering thepossible sources of errors in SRL and MD datasets, the rup-ture length of a few kilometers that we observed (allied withthe measured MD values of 10–15 cm) are consistent with


those expected for an event of this magnitude. Based on theworldwide catalog of Stirling et al. (2002), developed on areassessment and expansion of Wells and Coppersmith(1994) data, we obtain Mw 6.2 for SRL � 2:6 and Mw 6.5for SRL � 6 (their Table II). Values of MS 5.9 for SRL �2:6 and MS 6.2 for SRL � 6 come from the more local butwell-documented compilation of Pavlides and Caputo(2004), valid for dip-slip normal active faulting events inthe extensional tectonic regime of the Aegean region ofGreece (i.e., slip type and lithologies similar to those of theApennines). In this case, however, we face the problem of thelarge difference between local and moment magnitudes forthis earthquake and their scaling to MS, which is not avail-able. Regressions of average displacement (D) against SRLprovides 8 cm of D for 2.6 km of SRL and 18 cm for 6 km(Wells and Coppersmith, 1994) and higher values of D,

applying the formulas in Stirling et al. (2002), again suggest-ing low values of SRL based on the observed MD.

Notably, the fault was still slipping at surface afternearly one year (Degasperi, 2010) and the component ofafterslip was significant, approaching one half of the amountof coseismic slip observed at surface just after the event,2–3 cm in the first week or so, and 2.5 cm in the followingyear. The possibility of a large component of afterslip shouldbe kept in mind when comparing the maximum offset of anearthquake where the amount of postseismic slip is known(e.g., L’Aquila 2009) with those of other earthquakes inempirical SRL–MD databases for which only their total slipsare available (Wilkinson et al., 2010).

Slip along the antithetic Bazzano, Monte Caticchio, andFossa faults is interpreted here as secondary slip, accommo-dating the slip on the Paganica fault. The EMERGEO

Figure 14. The four hypotheses of distribution of coseismic surface faulting (see text for description). Basically, our estimate of a 2.6 kmprimary rupture agrees with EMERGEO results without discounting the possibility of a longer (up to 6 km) rupture. Longer primary surfaceruptures are suggested by other authors (13 km; Boncio et al., 2010; 19 km; Galli, Camassi, et al., 2009). The color version of this figure isavailable only in the electronic edition.


Working Group (2009a, 2009b) reached a similar conclu-sion, labeling most of the reactivations outside the Paganicafault as triggered slip. Secondary and sympathetic coseismicslip (Slemmons and DePolo, 1986) are common featuresalong faults near the primary seismogenic source of manyearthquakes (e.g., Murray et al., 1993; Çakir et al., 2003).However, coseismic ruptures along multiple fault segmentsare typical for surface-faulting earthquakes (e.g., Wesnousky,2008), as commonly observed in the Apennines (e.g., the 26September 1997,Mw 6.0 Colfiorito earthquake [Vittori et al.,2000, Cinti, 2007, Guerrieri et al., 2009]; the 23 November1980, MS 6.9 Irpinia earthquake [Blumetti, Esposito, et al.,2002; Porfido et al., 2002]; the 13 January 1915, MS 7.0Fucino earthquake [Michetti et al., 1996, Galadini and Galli,1999]) and in similar regions under active crustal extension(for instance, the February 1981, MS 6.5 Gulf of Corinthearthquake sequence [Jackson et al., 1982] and the 7 Sep-tember 1999, MS 5.9 Athens earthquake in Greece [Pavlideset al., 2002]; and the historical earthquakes of the Basin andRange Province in the western North America [dePoloet al., 1991]).

Conclusions

As expected for an event of this magnitude, appreciableslip occurred during the 2009 earthquake over a length of afew kilometers along the Paganica fault, while some negli-gible slip was triggered along several other fault strands (andwas only noticeable at surface in a few instances, even wherethe larger aftershocks took place; Fig. 1). In our judgment,there is not sufficient evidence to substantiate the interpreta-tion of some ground cracks located away from the Paganicafault as primary faulting. There are no general rules as towhat constitutes evidence of secondary effects versusprimary rupture. We have tried to give detailed justificationof our evidence for surface rupture length, but, more impor-tantly, with our perspective after other studies have beenpublished, we pointed out what the uncertainties are andthe lessons learned for future studies.

Indeed, according toWalters et al. (2009), only a portionof the observed seismic strain deficit in the area (Hunstadet al., 2003) was used by the 6 April event. The probabilityof future strong seismic events is now higher because theinduced Coulomb stress changes have brought some of thenearby faults closer to failure—some of which can generatestrong (M >6:5) earthquakes, based on the many geologicalstudies of the last decades (e.g., Blumetti et al., 1993; Barchiet al., 2000; Galadini and Galli, 2000; Pizzi et al., 2002;Boncio, Lavecchia and Pace, 2004; Roberts and Michetti,2004; Papanikolaou et al., 2005; Piccardi et al., 2006; Galliet al., 2008; Lavecchia et al., 2010).

The 2009 L’Aquila earthquake dramatically confirmedonce more the need for detailed geological studies in seismichazard assessments. The seismic hazard at L’Aquila wasalready known to be high based on historical data and theknowledge acquired in preceding decades on the major

active faults in the surrounding area, yet the exact locationof the causative fault and its earthquake potential were notfully understood. The Paganica fault, being not directlybacked by a major range front, is less evident on the land-scape when compared to nearby capable faults, such as thePettino, Stabiata, Gorzano, and Gran Sasso faults, which areinstead typical of the central Apennines scenery. However,the Paganica fault displays a clearly recent scarp and wasalready identified as a structure with late Quaternary activityby Bagnaia et al. (1992) and assumed as active by Boncio,Lavecchia, and Pace (2004) and Pace et al. (2006), mappedin detail during the CARG project (Sheet 359 “L’Aquila,”APAT, 2006), and recorded in the ITHACA database (Vittori,2000). Despite all this evidence, the hazard posed by thefault was completely overlooked during recent local urbandevelopment. This pinpoints the need to pay due attentionalso to seemingly minor structures, especially to guide land-use planning through precise geological mapping. The riskassociated with such faults, stemming from both groundmotion and ground rupture, were severely illustrated by thehuman and economic losses associated with the L’Aquilaearthquake. This is an increasingly probable perspective inmany countries of the Mediterranean region, due to the fre-quency of similar moderate seismic events and the growingdensity of population and vulnerable industrial facilities.

Trench exposures of the Paganica fault (Cinti et al.,2009; Galli, Giaccio, et al., 2009; Boncio et al., 2010;Pantosti et al., 2010) and other nearby faults, such as theMonte Marine, Pettino, and Campo Imperatore faults (e.g.,Galli et al., 2008, and references therein), show unequivocalevidence of larger offsets during past paleoseismic events,attributable to M >6:5 events. Furthermore, the amount offault rupture of the 2009 event is significantly lower thanthat of the 2 February 1703 earthquake (Blumetti, 1995).Therefore, an objective comparison of the scenarios ofgeological effects, as emerging from paleoseismologicaland historical data, indicates that the 2009 event, althoughdestructive, is far from representing the maximum credibleearthquake for the L’Aquila region.

Data and Resources

The focal mechanisms of Mediterranean earthquakes areavailable in the Regional Centroid Moment Tensors (RCMT)catalog at http://www.bo.ingv.it/RCMT (last accessedDecember 2010).

The Italian Seismic Instrumental and Parametric Data-basE (ISIDe) was searched using http://iside.rm.ingv.it/iside/standard/index.jsp (last accessed December 2010).

DInSAR images of the L’Aquila earthquake and theimages provided by IREA-CNR and INGV are availablefrom www.esa.int/esaCP/SEM4PJ9NJTF_index_0.html (lastaccessed December 2010).

The Catalogo Parametrico dei Terremoti Italiani (CPTI;Gruppo di Lavoro CPTI, 2004) is available from http://emidius.mi.ingv.it/CPTI99/ (last accessed December 2010).


http://www.bo.ingv.it/RCMT




http://iside.rm.ingv.it/iside/standard/index.jsp






http://www.esa.int/esaCP/SEM4PJ9NJTF_index_0.html




http://emidius.mi.ingv.it/CPTI99/





The ITalian HAzards from CApable Faults catalog(ITHACA) is available at http://sgi1.isprambiente.it/geoportal/catalog/content/ithaca.page (last accessed December 2010).

The maps in Figure 10 are from Bing Maps (Fig. 10b;http://www.bing.com/maps/) and GeoEye Ikonos imageoffered by Google Earth (Fig. 10c; http://google-latlong.blogspot.com/2009/04/laquila-italy-earthquake-imagery.html).

Acknowledgments

We appreciate the thorough review of our manuscript by twoanonymous referees. We are indebted to Leonello Serva, head of theGeological Survey of Italy, for his support and many suggestions that havegreatly improved this manuscript. Work done by G.S., A.B., and F.L. hasbeen supported by a special grant of the Insubria University to A.M.M. Thisresearch has also benefited from funding provided by the Italian Presidenzadel Consiglio dei Ministri–Dipartimento della Protezione Civile (DPC);scientific papers funded by DPC do not represent its official opinionand policies. Part of this study was funded by Natural Environment ResearchCouncil (NERC) Urgency Grant NE/H003266/1 and NERC Standard GrantNE/E01545X/1.

References

Ambrosetti, P., F. Carraro, G. Deiana, and F. Dramis (1982). Il sollevamentodell’Italia centrale tra il Pleistocene inferiore e il Pleistocene medio,Contributi conclusivi per la realizzazione della Carta Neotettonicad’Italia, CNR-Progetto Finalizzato Geodinamica, pubblicazione n.513, 219–223.

Anzidei, M., E. Boschi, V. Cannelli, R. Devoti, A. Esposito, A. Galvani,D. Melini, G. Pietrantonio, F. Riguzzi, V. Sepe, and E. Serpelloni(2009). Coseismic deformation of the destructive April 6, 2009L’Aquila earthquake (central Italy) from GPS data, Geophys. Res.Lett. 36, L17307, doi 10.1029/2009GL039145

Amoruso, A., and L. Crescentini (2009). Slow diffusive fault slip propaga-tion following the 6 April 2009 L’Aquila earthquake, Italy, Geophys.Res. Lett. 36, L24306, doi 10.1029/2009GL041503.

Agenzia per la Protezione dell'Ambiente ed i servizi Tecnici [APAT],Servizio Geologico d’Italia (2006). 359 L’Aquila. Carta Geologicad’Italia alla scala 1:50000. S.EL.CA., Firenze, Italy.

Atzori, S., I. Hunstad, M. Chini, S. Salvi, C. Tolomeo, C. Bignami,S. Stramondo, E. Transatti, A. Antonioli, and E. Boschi (2009).Finite fault inversion of DInSAR coseismic displacement of the2009 L’Aquila earthquake (central Italy), Geophys. Res. Lett. 36,L15305, doi 10.1029/2009GL039293.

Bagnaia, R., A. D’Epifanio, and S. S. Labini (1992). Aquilan and Subaequanbasins: An example of Quaternary evolution in central Apennines,Italy, Quaternaria Nova 2, 187–209.

Baratta, M. (1901). I terremoti d'Italia, Arnaldo Forni Editore, Torino, Italy,pp. 952

Barbano, M. S., R. Azzaro, R. Camassi, I. Cecic, S. D’Amico, A. Mostaccio,L. Scarfì, A. Tertulliani, and T. Tuvè (2009). The L’Aquila 2009earthquake: An application of the European Macroseismic Scale tothe damage survey, in Riassunti estesi delle comunicazioni del 28°Convegno Nazionale del Gruppo Nazionale di Geofisica della TerraSolida (GNGTS), 433–437.

Barchi, M., F. Galadini, G. Lavecchia, P. Messina, A. M. Michetti,L. Peruzza, A. Pizzi, E. Tondi, and E. Vittori (2000). Sintesi delleconoscenze sulle faglie attive in Italia centrale, Consiglio Nazionaledelle Ricerche—Gruppo Nazionale per la Difesa dai Terremoti, 62 pp.

Bertini, T., and C. Bosi (1993). La tettonica quaternaria della conca di Fossa(L’Aquila), Il Quaternario 6, 293–314.

Blumetti, A. M. (1995). Neotectonic investigations and evidence of paleo-seismicity in the epicentral area of the January–February 1703 central

Italy earthquakes, in Perspectives in Paleoseismology L. Serva(Editor), Bulletin of the American Association of EngineeringGeologists, Special Volume 6, Boston, Massachusetts, 83–100.

Blumetti, A. M., and L. Guerrieri (2007). Fault-generated mountain frontsand the identification of fault segments: Implications for seismichazard assessment, Boll. Soc. Geol. It. (Ital. J. Geosci.) 126, no. 2,307–322.

Blumetti, A. M., M. Di Filippo, P. Zaffiro, P. Marsan, and B. Toro (2002).Seismic hazard characterization of the city of L’Aquila (Abruzzo,central Italy): New data from geological, morphotectonic and gravityprospecting analyses, in F. Dramis, P. Farabollini, and P. Molin(Editors) Proceedings of the International Workshop “Large-scalevertical movements and related gravitational processes”—Cameri-no-Roma, 21–26 June, 1999, Studi Geologici Camerti, Numero Spe-ciale 2002, 7–18.

Blumetti, A. M., F. Dramis, and A. M. Michetti (1993). Fault generatedmountain fronts in the Central Apennines (Central Italy): geomorpho-logical features and seismotectonic implications, Earth Surf. Process.Landf. 18, 203–223.

Blumetti, A. M., V. Comerci, P. Di Manna, L. Guerrieri, and E. Vittori(2009). Geological effects induced by the L’Aquila earthquake (6 April2009; ML � 5:8) on the natural environment, Preliminary Report.38 pp., available at http://www.apat.gov.it/site/_files/Inqua/2009_abruzzo_earthquake_report.pdf (last accessed May 2011).

Blumetti, A. M., V. Comerci, L. Guerrieri, A. M. Michetti, L. Serva, andE. Vittori (2010). Is the April 6th 2009 L’Aquila earthquake a confir-mation of the “seismic landscape” concept?, European GeosciencesGeneral Assembly, 2–7 May 2010, Vienna, Austria, Session “One yearafter the Abruzzo 2009 earthquake,” TS8.1/G16/GD2.11/GM1.2/GMPV46/HS13.1/MPRG18/NH4.5/SM7.1, Geophysical ResearchAbstracts, 12, EGU2010-12050-1.

Blumetti, A. M., E. Esposito, L. Ferreli, A. M. Michetti, S. Porfido, L. Serva,and E. Vittori (2002). New data and reinterpretation of the November23, 1980, M 6.9 Irpinia-Lucania earthquake (southern Apennines)—coseismic surface effects, Studi Geologici Camerti, Num. Spec. 2002,19–27.

Boncio, P., G. Lavecchia, and B. Pace (2004). Defining a model of 3Dseismogenic sources for seismic hazard assessment applications:The case of central Apennines (Italy), J. Seismol. 8, 407–425.

Boncio, P., G. Lavecchia, G. Milana, and B. Rozzi (2004). Seismogenesis incentral Apennines, Italy: An integrated analysis of minor earthquakesequences and structural data in the Amatrice-Campotosto area, Ann.Geophys. 47, 1723–1742.

Boncio, P., A. Pizzi, F. Brozzetti, G. Pomposo, G. Lavecchia, D. Di Naccio,and F. Ferrarini (2010). Coseismic ground deformation of the 6 April2009 L’Aquila earthquake (central Italy, Mw 6.3), Geophys. Res. Lett.37, L06308, doi 10.1029/2010GL042807.

Boschi, E., G. Ferrari, P. Gasperini, E. Guidoboni, G. Smriglio, andG. Valensise (1995). Catalogo dei Forti Terremoti in Italia dal 461a.C. al 1980, Istituto Nazionale di Geofisica, Roma-SGA, Italy,973 pp.

Boschi, E., E. Guidoboni, G. Ferrari, G. Valensise, and P. Gasperini (1997).Catalogo dei Forti Terremoti in Italia dal 461 a.C. al 1990, IstitutoNazionale di Geofisica, Roma-SGA, Italy, 644 pp.

Çakir, Z., J.-B. de Chabalier, R. Armijo, B. Meyer, A. Barka, and G. Peltzer(2003). Coseismic and early post-seismic slip associated with the 1999Izmit earthquake (Turkey), from SAR interferometry and tectonic fieldobservations, Geophys. J. Int. 155, no. 1 93–110.

Cello, G., S. Mazzoli, and E. Tondi (1998). The 1703 seismic sequence ofcentral Italy: A major evidence of a crustal seismogenic zone in theUmbria-Marche-Abruzzi Apennines, J. Geodyn. 26, 443–460.

Cheloni, D., N. D’Agostino, E. D’Anastasio, A. Avallone, S. Mantenuto,R. Giuliani, M. Mattone, S. Calcaterra, P. Gambino, D. Dominici,F. Radicioni, and G. Fastellini (2010). Coseismic and initial postseis-mic slip of the 2009 Mw 6.3 L’Aquila earthquake, Italy, from GPSmeasurements, Geophys. J. Int. 181, no. 3, 1539–1546, doi 10.1111/j.1365-246X.2010.04584.x.


http://sgi1.isprambiente.it/geoportal/catalog/content/ithaca.page





http://www.bing.com/maps/



http://google-latlong.blogspot.com/2009/04/laquila-italy-earthquake-imagery.html



http://dx.doi.org/10.1029/2009GL039145

http://dx.doi.org/10.1029/2009GL041503

http://dx.doi.org/10.1029/2009GL039293

http://www.apat.gov.it/site/_files/Inqua/2009_abruzzo_earthquake_report.pdf






http://dx.doi.org/10.1029/2010GL042807

http://dx.doi.org/10.1111/j.1365-246X.2010.04584.x

http://dx.doi.org/10.1111/j.1365-246X.2010.04584.x

Chiarabba, C., A. Amato, M. Anselmi, P. Baccheschi, I. Bianchi,M. Cattaneo, G. Cecere, L. Chiaraluce, M. G. Ciaccio, P. De Gori,G. De Luca, M. Di Bona, R. Di Stefano, L. Faenza, A. Govoni,L. Improta, F. P. Lucente, A. Marchetti, L. Margheriti, F. Mele,A. Michelini, G. Monachesi, M. Moretti, M. Pastori, N. P. Agostinetti,D. Piccinini, P. Roselli, D. Seccia, and L. Valoroso (2009). The 2009L’Aquila (central Italy) Mw 6.3 earthquake: Main shock and after-shocks, Geophys. Res. Lett. 36, L18308, doi 10.1029/2009GL039627.

Cinti, F. R. (2007). Surface fractures associated with the 1997 Umbria-Marche earthquake sequence: Prospects from a decade of surveys, ana-lyses and debates, in S. Barba, L. Luzi, P. Montone, and S. Stramondoet al. (Ed.), The Colfiorito earthquake 1997–2007: Ten Years On.Extended Abstracts, 8–10/10/2007, Istituto Nazionale di Geofisica eVulcanologia, Rome, Italy, 7–9, http://hdl.handle.net/2122/2533.

Cinti, F. R., R. Civico, L. Cucci, P. M. De Martini, D. Pantosti,S. Pierdominici, S. Pucci, andC.A.Brunori (2009). Looking for surfacefaulting ancestors of the L’Aquila April 6, 2009 event: Preliminarypaleoseismological data and seismic hazard implications, in Riassuntiestesi delle comunicazioni del 28° Convegno Nazionale del GruppoNazionale di Geofisica della Terra Solida (GNGTS), 27–29.

D’Agostino, N., A. Avallone, D. Cheloni, E. D’Anastasio, S. Mantenuto,and G. Selvaggi (2008). Active tectonics of the Adriatic region fromGPS and earthquake slip vectors, J. Geophys. Res. 113, no. B12413,doi 10.1029/2008JB005860.

D’Agostino, N., F. Dramis, R. Funiciello, and J. Jackson (2001). Interactionsbetween mantle upwelling, drainage evolution and active normalfaulting: An example from the central Apennines (Italy), Geophys.J. Int. 147, 475–497.

D’Agostino, N., F. Speranza, and R. Funiciello (1997). Stili e geometriedella tettonica estensionale quaternaria nell’Appennino Centrale:L’area del Gran Sasso d’Italia, Il Quaternario 10, no. 2, 389–394.

Degasperi, M. (2010). Relazione sui monitoraggi nella zona di Paganica.Provincia Autonoma di Trento, Servizio Geologico, Report Marzo2010, available at http://www.protezionecivile.tn.it/geologico/images/Notizie2010/abruzzo/report_03_2010+ALL.pdf (last accessed May2011).

dePolo, C. M., D. G. Clark, D. B. Slemmons, and A. R. Ramelli (1991).Historical surface faulting in the Basin and Range province, westernNorth America: Implications for fault segmentation, J. Struct. Geol.13, 123–136.

Devoti, R., F. Riguzzi, M. Cuffaro, and C. Doglioni (2008). New GPSconstraints on the kinematics of the Apennines subduction, EarthPlanet. Sci. Lett. 273, 163–174, doi 10.1016/j.epsl.2008.06.031.

Demangeot, J. (1965). Géomorphologie des Abruzzes Adriatiques.Memoirs et documents, Editions du Center National de la RechercheScientifique, Paris, France, 403 pp.

Doglioni, C., E. Gueguen, P. Harabaglia, and F. Mongelli (1999). On theorigin of W-directed subduction zones and applications to the westernMediterranean, Geol. Soc. Sp. Publ. 156, 541–561.

Dramis, F. (1993). Il ruolo dei sollevamenti tettonici a largo raggio nellagenesi del rilievo appenninico, Studi Geol. Camerti Vol. Spec. 1992,no. 1, 9–16.

Dramis, F., and A. M. Blumetti (2005). Some considerations concerningseismic geomorphology and paleoseismology, Tectonophysics 408,177–191.

EMERGEOWorking Group (2009a). Rilievi geologici nell’area epicentraledella sequenza sismica dell’aquilano del 6 Aprile 2009, in QuaderniGeofisc., 70, ISSN 1590-2595, 1–53.

EMERGEO Working Group (2009b). Evidence for surface ruptureassociated with the Mw 6.3 L’Aquila earthquake sequence of April2009, central Italy (2010), Terra Nova 22, 43–51, doi 10.1111/j.1365-3121.2009.00915.x

Falcucci, E., S. Gori, E. Peronace, G. Fuselli, M.Moro,M. Saroli, B. Giaccio,P.Messina, G. Naso, G. Scardia, A. Sposato,M. Voltaggio, P. Galli, andF. Galadini (2009). The Paganica fault and surface coseismic rupturescaused by the 6 April 2009 earthquake (L’Aquila, central Italy),Seismol. Res. Lett. 80, no. 6, 940–950.

Farabollini, P., F. Agosta, D. Aringoli, M. Materazzi, P. Pierantoni, andE. Tondi (2009). Il terremoto aquilano del 6 aprile 2009: Rilievigeologici di superficie e prime considerazioni, University of Camerinoreport, http://www.unich.it/geosis/rif/Farabollini_et‑al_Chieti2009.pdf(last accessed May 2011).

Faure Walker, J. P., G. P. Roberts, P. Sammonds, and P. A. Cowie (2010).Comparison of earthquakes strains over 102 and 104 year timescales:Insights into variability in the seismic cycle in the central Apennines,Italy, J. Geophys. Res. B Solid Earth Planets, doi 10.1029/2009JB006462.

Galadini, F., and P. Galli (1999). The Holocene paleoearthquakes on the1915 Avezzano earthquake faults (central Italy): Implications for activetectonics in central Apennines, Tectonophysics 308, 143–170.

Galadini, F., and P. Galli (2000). Active tectonics in the central Apennines(Italy)—input data for seismic hazard assessment, Nat. Hazards 22,225–270.

Galadini, F., and P. Galli (2003). Paleoseismology of silent faults in thecentral Apennines (Italy): The Mt. Vettore and Laga Mts. faults,Ann. Geophys 46, no. 5, 815–836.

Galli, P., R. Camassi, R. Azzaro, F. Bernardini, S. Castenetto, D. Molin,E. Peronace,A. Rossi,M.Vecchi, andA. Tertulliani (2009). Il terremotoaquilano del 6 Aprile 2009: Rilievo macrosismico, effetti di superficieed implicazioni sismotettoniche, Il Quaternario 22, no. 2, 235–246.

Galli, P., F. Galadini, M. Moro, and C. Giraudi (2002). New paleoseismo-logical data from the Gran Sasso d’Italia area (central Apennines),Geophys. Res. Lett. 29, no. 7, 4, doi 10.1029/2001GL013292.

Galli, P., F. Galadini, and F. Calzoni (2005). Surface faulting in Norcia(central Italy): A “paleoseismological perspective, Tectonophysics403, no. 1–4, 117–130.

Galli, P., F. Galadini, and D. Pantosti (2008). Twenty years of paleoseismol-ogy in Italy, Earth Sci. Rev. 88, 89–117.

Galli, P., B. Giaccio, P. Messina, and E. Peronace (2009). Paleoseismologi-cal news from L’Aquila faults, in Riassunti estesi delle comunicazionidel 28° Convegno Nazionale del Gruppo Nazionale di Geofisica dellaTerra Solida (GNGTS), 34–37.

Giraudi, C., and M. Frezzotti (1995). Paleoseismicity in the Gran Sassomassif (Abruzzo, central Italy), Quat. Int. 25, no. 81–93.

Gruppo di Lavoro CPTI (2004). Catalogo Parametrico dei TerremotiItaliani, versione 2004 (CPTI04), INGV, Bologna, Italy, http://emidius.mi.ingv.it/CPTI/ (last accessed May 2011).

Gueguen, E., C. Doglioni, and M. Fernandez (1998). On the post 25 Mageodynamic evolution of the western Mediterranean, Tectonophysics298, 259–269.

Guerrieri, L., G. Baer, R. Amit, A. M. Blumetti, V. Comerci, P. Di Manna,Y. Hamiel, A. M. Michetti, A. Salamon, A. Mushkin, G. Sileo, andE. Vittori (2010). InSAR data as a field guide for mapping minor earth-quake surface ruptures: The case of the 2009 L’Aquila, central Italy,earthquake, J. Geophys. Res. B Solid Earth Planets 115, no. B12331,16 pp., doi 10.1029/2010JB007579.

Guerrieri, L., A. M. Blumetti, E. Esposito, A. M. Michetti, S. Porfido,L. Serva, E. Tondi, and E. Vittori (2009). Capable faulting, environmen-tal effects and seismic landscape in the area affected by the Umbria-Marche (central Italy) seismic sequence, Tectonophysics 476, no.1-2, 269–281, doi 10.1016/j.tecto.2008.10.034.

Guidoboni, E. (2009). I terremoti storici dell’area aquilana: Prezioseinformazioni, con qualche ombra, Geoitalia 28, 30–37.

Guidoboni, E., G. Ferrari, D. Mariotti, A. Comastri, G. Tarabusi, andG. Valensise (2007). CFTI4Med, Catalogue of Strong Earthquakesin Italy (461 B.C.–1997) and Mediterranean Area (760 B.C.–1500),INGV-SGA. Available from http://storing.ingv.it/cfti4med/ (last ac-cessed November 2010).

Hunstad, I., G. Selvaggi, N. D’Agostino, P. England, P. Clarke, andM. Pierozzi (2003). Geodetic strain in peninsular Italy between1875 and 2001, Geophys. Res. Lett. 30, no. 4, 1181, doi 10.1029/2002GL016447.

Jackson, J. A., J. Gagnepain, G. Houseman, G. C. P. King, P. Papadimitriou,C. Soufleris, and J. Virieux (1982). Seismicity, normal faulting, and the


http://dx.doi.org/10.1029/2009GL039627

http://hdl.handle.net/2122/2533



http://dx.doi.org/10.1029/2008JB005860

http://www.protezionecivile.tn.it/geologico/images/Notizie2010/abruzzo/report_03_2010+LL.pdf






http://dx.doi.org/10.1016/j.epsl.2008.06.031

http://dx.doi.org/10.1111/j.1365-3121.2009.00915.x

http://dx.doi.org/10.1111/j.1365-3121.2009.00915.x

http://www.unich.it/geosis/rif/Farabollini_et-al_Chieti2009.pdf




http://dx.doi.org/10.1029/2009JB006462

http://dx.doi.org/10.1029/2009JB006462

http://dx.doi.org/10.1029/2001GL013292

http://emidius.mi.ingv.it/CPTI/





http://dx.doi.org/10.1029/2010JB007579

http://dx.doi.org/10.1016/j.tecto.2008.10.034

http://storing.ingv.it/cfti4med/



http://dx.doi.org/10.1029/2002GL016447

http://dx.doi.org/10.1029/2002GL016447

geomorphological development of the Gulf of Corinth (Greece): TheCorinth earthquakes of February and March 1981, Earth Planet. Sci.Lett. 57, 377–397.

Lanari, R., P. Berardino, M. Bonano, F. Casu, A. Manconi, M. Manunta,M. Manzo, A. Pepe, S. Pepe, E. Sansosti, G. Solaro, P. Tizzani,and G. Zeni (2010). Surface displacements associated with theL’Aquila 2009 Mw 6.3 earthquake (central Italy): New evidence fromSBAS-DInSAR time series analysis, Geophys. Res. Lett. 37, L20309,doi 10.1029/2010GL044780.

Lavecchia, G., P. Boncio, F. Brozzetti, R. De Nardis, D. Di Naccio,F. Ferrarini, A. Pizzi, and G. Pomposo (2010). The April 2009 Aquila(central Italy) seismic sequence (Mw 6.3): A preliminary seismotec-tonic picture, in Recent Progress on Earthquake Geology P. Guarnieri(Editor), Nova Publishers, NewYork, ISBN/ISSN 978-1-60876-147-0,1–17.

Malinverno, A., and W. B. F. Ryan (1986). Extension in the Tyrrhenian Seaand shortening in the Apennines as result of arc migration driven bysinking in the lithosphere, Tectonics 5, 227–245.

Messina, P., P. Galli, B. Giaccio, and E. Peronace (2009). Quaternarytectonic evolution of the area affected by the Paganica fault (2009L’Aquila earthquake), in Riassunti estesi delle comunicazioni del28° Convegno Nazionale del Gruppo Nazionale di Geofisica dellaTerra Solida (GNGTS), 47–50.

Michetti, A. M., F. Audemard, and S. Marco (2005). Future trends inpaleoseismology: Integrated study of the seismic landscape as a vitaltool in seismic hazard analyses, in Paleoseismology, Integrated Studyof the Quaternary Geological Record for Earthquake Deformationand Faulting A. M. Michetti, F. Audemard, and S. Marco (Editors),Special Issue, Tectonophysics 408, no. 1–4, 3–21.

Michetti, A. M., F. Brunamonte, L. Serva, and E. Vittori (1996). Trenchinvestigations along the 1915 Fucino earthquake fault scarps(Abruzzo, central Italy): Geological evidence of large historical events,J. Geophys. Res. 101, 5921–5936.

Michetti, A. M., E. Esposito, L. Guerrieri, S. Porfido, L. Serva,R. Tatevossian, E. Vittori, F. Audemard, T. Azuma, J. Clague,V. Comerci, A. Gurpinar, J. McCalpin, B. Mohammadioun,N. A. Morner, Y. Ota, and E. Roghozin (2007). Intensity Scale ESI2007, in Memorie Descrittive Carta Geologica d’Italia L. Guerrieriand E. Vittori (Editors), APAT, Servizio Geologico d’Italia—Dipartimento Difesa del Suolo, Roma, Italy, 74, 53 pp.

Moro, M., V. Bosi, F. Galadini, P. Galli, B. Giaccio, P. Messina, andA. Sposato (2002). Analisi paleosismologiche lungo la faglia delM. Marine (alta valle dell’Aterno): Risultati preliminari, Il Quaternar-io 15, 267–278.

Murray, M. H., J. C. Savage, M. Lisowski, and W. K. Gross (1993).Coseismic displacements: 1992 Landers, California, Earthquake,Geophys. Res. Lett. 20, no. 7, 623–626.

Nijman, W. (1971). Tectonics of the Velino-Sirente area, Abruzzi,central Italy: Modification of compressional structures by subsequentdilatation and collapse, Koninkl. Nederl. Akademie Van Wetenshap-pen, Amsterdam, The Netherlands, Proceedings of the meeting ofOctober 31, 1970, Series B, 74, no. 2, 156–184.

Pace, B., L. Peruzza, G. Lavecchia, and P. Boncio (2006). Layeredseismogenic source model and probabilistic seismic-hazard analysesin central Italy, Bull. SeismOL. Soc. Am. 96, 107–132, doi 10.1785/0120040231.

Pantosti, D., F. R. Cinti, P. M. De Martini, S. Pucci, R. Civico,S. Pierdominici, L. Cucci, C. A. Brunori, A. Patera, and S. Pinzi(2010). Discovering the characteristics of the surface faulting ancestorsof the L’Aquila April 6, 2009 earthquake by paleoseismologicalinvestigations, European Geosciences General Assembly, 2–7 May2010, Vienna, Austria, Geophysical Research Abstracts, 12,EGU2010-9673.

Pantosti, D., G. D’Addezio, and F. Cinti (1996). Paleoseismicity of theOvindoli-Pezza fault, central Apennines, Italy: A history including alarge previously unrecorded earthquake in the Middle Age (860–1300A.D.), J. Geophys. Res. 101, 5937–5959.

Papanikolaou, I. D., M. Foumelis, I. Paracharidis, E. L. Lekkas, andG. Fountoulis (2010). Deformation pattern of the 6 and 7 April2009,Mw � 6:3 andMw � 5:6 earthquakes in L’Aquila (central Italy)revealed by ground and space observations, Nat. Hazards Earth Syst.Sci. 10, 73–87.

Papanikolaou, I. D., G. P. Roberts, and A. M. Michetti (2005). Fault scarpsand deformation rates in Lazio-Abruzzo, central Italy: Comparisonbetween geological fault slip rate and GPS data, Tectonophysics408, 147–176, doi 10.1016/j.tecto.2005.05.043.

Patacca, E., R. Sartori, and P. Scandone (1990). Tyrrhenian basin andApenninic arcs. Kinematic relations since late Tortonian times,Mem. Soc. Geol. It 45, 425–451.

Pavlides, S. B., and R. Caputo (2004). Magnitude versus faults’ surfaceparameters: Quantitative relationships from the Aegean, Tectonophy-sics 380, 3–4, 159–188.

Pavlides, S. B., A. Ganas, and G. A. Papadopoulos (2002). The fault thatcaused the Athens September 1999 Ms � 5:9 earthquake: Fieldobservations, Nat. Hazards 27, 61–84.

Piccardi, L., F. Sani,M. Bonini,M. Boccaletti, G.Moratti, andA. Gualtierotti(1997). Deformazioni quaternarie nell’Appennino Centro-Settentrionale: Evidenze ed implicazioni, Il Quaternario 10, no. 2,273–280.

Piccardi, L., F. Sani, G. Moratti, D. Cunningham, and E. Vittori (2011).Present geodynamics of the circum-Adriatic region: An overview,J. Geodyn. 51, 81–89, doi 10.1016/j.jog.2010.09.002

Piccardi, L., E. Tondi, and G. Cello (2006). Geo-structural evidence foractive oblique extension in south-central Italy, in The AdriaMicroplate: GPS Geodesy, Tectonics and Hazards, NATO ScienceSeries IV, Earth and Environmental Sciences, N. Pinter, G. Grenerczy,J. Weber, S. Stein, and D. Medak (Editors), Vol. 61, Springer,Netherlands, ISBN 978-1-4020-4234-8, 95–108.

Pizzi, A., F. Calamita, M. Coltorti, and P. Pieruccini (2002). Quaternarynormal faults, intramontane basins and seismicity in the Umbria-Marche-Abruzzi Apennine ridge (Italy): Contribution of neotectonicanalysis to seismic hazard assessment, Boll. Soc. Geol. It. Spec. Publ. 1,923–929.

Porfido, S., E. Esposito, E. Vittori, G. Tranfaglia, A. M. Michetti,A. M. Blumetti, L. Ferreli, L. Guerrieri, and L. Serva (2002). Arealdistribution of ground effects induced by strong earthquakes insouthern Apennines (Italy), Surv. Geophys. 23, no. 6, 529–562.

Roberts, G. P., and A. M. Michetti (2004). Spatial and temporal variations ingrowth rates along active normal fault systems: An example from theLazio-Abruzzo Apennines, central Italy, J. Struct. Geol. 26 339–376,doi 10.1016/S0191-8141(03)00103-2.

Roberts, G. P., B. Raithatha, G. Sileo, A. Pizzi, S. Pucci, J. F. Walker,M. Wilkinson, K. McCaffrey, R. Phillips, A. M. Michetti, L. Guerrieri,A. M. Blumetti, E. Vittori, P. Sammonds, P. Cowie, P. Galli, andR. Walters (2010). Shallow subsurface structure of the 2009 April 6Mw 6.3 L’Aquila earthquake surface rupture at Paganica, investigatedwith ground-penetrating radar, Geoph. J. Int. 183, 774–790,doi 10.1111/j.1365-246X.2010.04713.x.

Serva, L., A. M. Blumetti, L. Guerrieri, and A. M. Michetti (2002). TheApennine intermountain basins: The result of repeated strong earth-quakes over a geological time interval, Boll. Soc. Geol. It. 1, 939–946.

Sileo, G., M. Wilkinson, A. M. Michetti, G. P. Roberts, K. J. W. McCaffrey,P. A. Cowie, R. J. Phillips, T. Wright, A. Berlusconi, F. Livio,A. M. Blumetti, L. Guerrieri, E. Vittori, P. Allasia, M. Baldo,D. Giordan, G. Lollino, L. La Rocca, F. Guzzetti, E. Esposito,S. Porfido, P. Campedel, S. Cocco, S. Barba, and L. Piccardi (2009).Multidisciplinary study of post-seismic deformation for the April 6,2009, L’Aquila earthquake, Riassunti estesi delle comunicazioni del28° Convegno Nazionale del Gruppo Nazionale di Geofisica dellaTerra Solida (GNGTS), 67–69.

Slemmons, D. B., and C. M. de Polo (1986). Evaluation of active faultingand related hazard, in Active Tectonics, Studies in GeophysicsR. E. Wallace (Editor), National Academy Press, Washington, D.C.,45–62.


http://dx.doi.org/10.1029/2010GL044780

http://dx.doi.org/10.1785/0120040231

http://dx.doi.org/10.1785/0120040231

http://dx.doi.org/10.1016/j.tecto.2005.05.043

http://dx.doi.org/10.1016/j.jog.2010.09.002

http://dx.doi.org/10.1016/S0191-8141(03)00103-2

Stirling, M. W., D. Rhoades, and K. R. Berryman (2002). Comparison ofearthquake scaling relations derived from data of the instrumentaland preinstrumental era, Bull. Seismol. Soc. Am. 92, 812–830.

Tertulliani, A., A. Rossi, L. Cucci, and M. Vecchi (2009). L’Aquila (centralItaly) earthquakes: The predecessors of the April 6, 2009 event,Seismol. Res. Lett. 80, no. 6, 972–977, doi 10.1785/gssrl.80.6.1008.

Valensise, G. (2009). Faglie attive e terremoti: Tempo di cambiare strategie,Geoitalia 28, 12–17.

Vezzani, L., and F. Ghisetti (1998). Carta Geologica dell’Abruzzo.S.EL.CA., Firenze, Italy.

Vittori, E. (2000). State of the art of active fault studies in Italy, in Abstractsvolume on CD-ROM, 5 p., Proceedings of the 31st InternationalGeological Congress, Rio de Janeiro, Brasil, 6–17 August 2000.

Vittori, E., G. Deiana, E. Esposito, L. Ferreli, L. Marchegiani, G. Mastrolor-enzo, A.M.Michetti, S. Porfido, L. Serva, A. L. Simonelli, and E. Tondi(2000). Ground effects and surface faulting in the September–October1997 Umbria-Marche (Central Italy) seismic sequence, J. Geodyn. 29,535–564.

Walters, R. J., J. R. Elliott, N. D’Agostino, P. C. England, I. Hunstad,J. A. Jackson, B. Parsons, R. J. Phillips, and G. Roberts (2009).The 2009 L’Aquila earthquake (central Italy): A source mechanismand implications for seismic hazard, Geophys. Res. Lett. 36,L17312, 6 pp., doi 10.1029/2009GL039337.

Wells, D. L., and K. L. Coppersmith (1994). New empirical relationshipsamong magnitude, rupture width, rupture area, and surface displace-ment, Bull. Seismol. Soc. Am. 84, 974–1002.

Wesnousky, S. G. (2008). Displacement and geometrical characteristics ofearthquake surface ruptures: Issues and implications for seismic-hazard analysis and the process of earthquake rupture, Bull. Seismol.Soc. Am. 98, no. 4, 1609–1632.

Wilkinson, M., K. J. W. McCaffrey, G. P. Roberts, P. A. Cowie, R. J. Phillips,A. M. Michetti, E. Vittori, L. Guerrieri, A. M. Blumetti, A. Bubeck,A. Yates, and G. Sileo (2010). Partitioned postseismic deformationassociated with the 2009 Mw 6.3 L’Aquila earthquake surface rupturemeasured using a terrestrial laser scanner, Geophys. Res. Lett. 37,L10309, 7 pp., doi 10.1029/2010GL043099.

Servizio Geologico d’ItaliaIstituto Superiore per la Protezione e la Ricerca Ambientale (ISPRA)Via Vitaliano Brancati48-00144 Rome, Italy

(E.V., P.D., A.M.B., V.C., L.G.)

Consiglio Nazionale delle Ricerche–Istituto per l’Ambiente Marino eCostieroCalata Porta di Massa80133 Naples, Italy

(E.E., S.P.)

Dipartimento Scienze Chimiche e AmbientaliUniversità dell’InsubriaVia Valleggio, 1122100, Como, Italy

(A.M.M., A.B., F.L., G.S.)

Consiglio Nazionale delle Ricerche–Istituto di Geoscienze e Georisorsevia G. La Pira 450121, Florence, Italy

(L.P.)

Research School of Earth SciencesBirkbeck/UCLUniversity of LondonGower StreetLondonWC1E 6BTUnited Kingdom

(G.P.R.)

Department of Earth SciencesDurham UniversityScience LabsDurhamDH1 3LEUnited Kingdom

(M.W., K.J.W.M.)

Institute of Geophysics and TectonicsSchool of Earth and EnvironmentUniversity of LeedsLeedsLS2 9LTUnited Kingdom

(R.J.P.)

Institute of GeographySchool of GeoSciencesUniversity of EdinburghDrummond StreetEdinburghEH8 9XPScotland, United Kingdom

(P.A.C.)

Manuscript received 24 May 2010


http://dx.doi.org/10.1785/gssrl.80.6.1008

http://dx.doi.org/10.1029/2009GL039337

http://dx.doi.org/10.1029/2010GL043099

Surface faulting of the 6 April 2009 Mw 6.3 L’Aquila earthquake in central Italy

Documents

Transcript of Surface faulting of the 6 April 2009 Mw 6.3 L’Aquila earthquake in central Italy