Journal of Geodetic Science• 3(1) • 2013 • 12-21 DOI: 10.2478/jogs-2013-0005 •

Strains arising by seismic events in theSIRGAS-CON network regionResearch ArticleG. S. Marotta1∗, G. S. França1, J. F. G. Monico2, R. A. Fuck3

1 Seismological Observatory - Geosciences Institute, University of Brasília, Campus Universitário Darcy Ribeiro,CEP:70910-900, Brasília/DF, Brazil

2 Department of Cartography - Faculty of Science and Technology, Paulista State University Júlio deMesquita Filho,Rua Roberto Simonsen 305, Centro Educacional, Presidente Prudente/SP, Brazil

3 Geochronology Laboratory - Geosciences Institute, University of Brasília, Campus Universitário Darcy Ribeiro,CEP:70910-900, Brasília/DF, Brazil

Abstract:In this study, we investigate surface strains related to seismic events and their relationship with pre- and post-seismic events in LatinAmerica, by analyzing the variation of estimated earth coordinates supplied by a geodetic network called SIRGAS-CON. Based on dataprovided by the USGS for the period 2000-2011, and after the Global Congruency test, we selected four events associated with unstablegeodetic network points. The resulting strains were estimated based on the nite element method using networks of points consideredunstable connected to neighboring points using the Delaunay triangulation. It was possible to determine the strains along with theresulting guidelines for pre- and post-seismic, considering each triangular lattice formed for analysis as a homogeneous solid body. Thecalculation of strains and veri cation of the results allowed to analyze the interactions between lithospheric plates from the contractionand extension directions between points located in different plates. Despite the association between seismic events and the strain ofgeodetic network, some events of magnitude greater than 5.8 Mw were excluded because it does not show (provide) the surface strain,which is located at great depths. It was con rmed that events of greater magnitude provide increased surface strain rate when comparedwith other similar depths.

Keywords:geodetic network • lithospheric plates • lithospheric plates • post-seismic • pre-seismic • surface strains.© Versita sp. z o.o.

Received 23-09-2012; accepted 31-01-2013

1. Introduction

Strain analysis, according to material mechanics concepts, hasbeen widely used in geodesy and geophysics in order to under-stand the geodynamic behavior and to investigate the impacts ofnatural and arti cial events on the earth surface.

Several studies have been conducted to analyze displacement andstrains resulting from energy accumulation or release caused bynatural forces that act on the crust and results in seismic events ofdifferent magnitudes and intensities in locations where there are

∗E-mail: marotta@unb.br

faults, fractures or lithospheric plate boundaries.

One of the rst tasks of the GPS (Global Positioning System) forgeophysical studies, was to determine displacement between pre-and post-seismic events according to Hudnut et al. (1994), in the7.2 moment magnitude (Mw ) - earthquake of June 28, 1992 thathappened in Landers, California. Hudnut et al. (1994) determinedthe displacements caused by this earthquake and used the data tomodel the elastic representation of the rupture planes of primaryfaults.

There are numerous studies involving seismicity analysis, the re-sulting strain on the surface and analyzing the temporal variationof geodetic control point coordinates as well. Among them, Yu etal. (2001), Fernandes et al. (2002), Ishii et al. (2005) and Hsu etal. (2009) studied co-, pre- and post-seismic movements of earth-

Unauthenticated | 68.107.139.75Download Date | 5/9/13 4:05 PM

Journal of Geodetic Science 13

quakes using GNSS (Global Navigation Satellite System) technol-ogy to determine the displacements and strains caused by differ-ent events.

Wallace et al. (2004) analyzed velocities measured by GPS and ob-tained earthquake slip vectors of faults in the Woodlark Basin inNew Guinea, to understand the orientation of the tectonic blocksand the degree of elastic strain along the region faults. Zhanget al. (2005) based on the results of the velocity eld of crustalmovements obtained from GPS measurements on the northeast-ern edge of Qinghai-Xizang block, analyzed qualitative and quan-titatively the movement and strain between blocks and tectonicfaults on their boundaries, distribution of the tectonic tension eldand locals with high accumulation of strain energy and intensity.Ruegg et al. (2009) analyzed the interseismic strain accumulationmeasured by GPS in the seismic gap in Chile, and reported thatsurface strain in the south central region between Concepción andConstitución is consistent with the elastic load on the subductioninterface at depth. Through seismic study and GPS positioningtechniques, Vigny et al. (2009) showed that in the analyzed areain Chile, part of the total convergence rate between the Nazca andSouth America plates gives rise to elastic strain accumulation onthe top plate and part is dissipated by free or non-seismic slip. InThailand, Satirapod et al. (2010) conducted studies focusing onGPS data collected between two large earthquakes and found thatthe strain was in the same direction of the post-seismic relaxationveri ed in the Sumatra trench. Velasco et al. (2010) analyzed a se-ries of vertical and horizontal crustal seismic re ection lines, GPScontinuous velocity and surfacegeology todetermine the relation-ships among interseismic strain accumulation, underground ge-ometry and slip rates of geological fault lines in the East Basin andRange Province, western United States.

In the case of natural forces acting on the lithosphere, more pre-cisely on the crust, it is understood that the study of strains associ-ated with seismic events remains not completely understood andtherefore, needs to be continuously studied.

The objective of this paper is to verify the in uence of seismicevents on the crust, this study aims to analyze the strains on theearth surface, in the pre- and post-seismic, using coordinates es-timated by GNSS positioning techniques in a continuously moni-tored geodetic network called SIRGAS-CON.

2. Experimental procedures

2.1. Study sites

Figure 1 shows the entire region encompassed by the SIRGAS-CONnetwork, which is the base for the Geocentric Reference System fortheAmericas (SIRGAS). Thede nition follows the IERS InternationalTerrestrial Reference System (ITRS) and its realization is compatiblewith the International Terrestrial Reference Frame (ITRF). The net-work is based on the contribution of more than 50 voluntary LatinAmerican organizations, that deploy, operate and voluntarily pro-vide the data for processing. The network encompasses about 250

Figure 1. SIRGAS-CON network (modifed from: www.sirgas.org

accessed on 20/03/2012).

continuous operating GNSS receivers (48 of thembelonging to theglobal IGS network) distributed all over the Americas, Caribbeanand Antarctica, encompassing the lithospheric plates of South andNorth America, Antarctica, Nazca, Cocos and Caribbean.

The SIRGAS Local Processing Centres compute sub-networks thatcompose the SIRGAS-CON and the DGFI (Deutsches GeodätischesForschungsinstitut) compute one core network, primary densi ca-tion of ITRF in Latin America. Afther, the SIRGAS Combination Cen-tres, formedbyDGFI and IBGE (Brazilian Institute of Geography andStatistics), combine all solutions to get homogeneous precision forstation positions and velocities in a continental level. At the timeof the work, it was reported on ITRF2005. Currently, the solutionsare reported weekly on IGS08, a realization of ITRF2008.

A study by Costa et al. (2009) determined the displacement veloc-ity vectors of plates by processing the data obtained from SIRGAS-CON network. Silva et al. (2010) used data from the same net-work to determine station displacements caused by the earth-quake of February 27, 2010, in Chile. The authors reported dis-placements that ranged from 3.3 to 297.8 cm at epicentral dis-tances of 1,000 km.

Unauthenticated | 68.107.139.75Download Date | 5/9/13 4:05 PM

Journal of Geodetic Science14

Table 1. Displacement of stations of the SIRGAS-CON network after the earthquakes that happened between 2000 and 2011 (Sànches and Seitz,2011, modified).

Location Date Magnitude Displacement Stations(Mw) (cm) affected

Comcepción - Chile 02/12/2011 6.1 2 CONZMechicali - Mexico 04/04/2010 7.2 23 MEXIChile 02/23/2010 8.8 1 to 305 23 stationsCosta Rica 01/08/2008 6.1 2 ETCGMartinique 11/29/2007 7.4 1 BDOS, GTK0Copiapo - Chile 04/30/2006 5.3 2 COPOTarapaca - Chile 06/13/2005 7.9 6 IQQEManagua - Nicaragua 10/09/2004 6.9 1 MANAArequipa - Peru 06/23/2001 8.4 52 AREQ

After studying the SIRGAS-CON network between 2000 and 2011,Sànches and Seitz (2011) showed the impact of seismic events onSIRGAS, as seen in Table 1.

2.2. Coordinate system

The coordinates of the SIRGAS-CON network, arranged in geocen-tric cartesian system (ellipsoid GRS80), are determined by weeklysolutionsof thedata suppliedby theGNSS station. The coordinatesare provided by the working groups responsible for maintainingSIRGAS (Brunini et al., 2012).

To determine the strains, it was necessary to transform the three-dimensional geocentric cartesian system (X , Y , Z ) into the geo-centric geodetic system (λ,ϕ,h) and from this, to the local geode-tic system (x , y, z). Monico (2008) presents the models used totransform the systems.

The geocentric geodetic coordinate system was used for both,forming connections between the geodetic points using the De-launay triangulation, and de ning the origin of the local geodeticsystem, given by the centroid position of each triangle.

After de ning the origin and points that make up each trianglecalled the network, the three-dimensional coordinates of its ver-tices were calculated in the local geodetic frame.

2.3. Stability points of the geodetic network

Before calculating the geodetic network strains, we used the GCT(Global Congruency Test) to identify the GNSS station points thatmoved between pre- and post-seismic events. This test is widelyused to verify statistically point stability.

Neumann and Kutterer (2006), Hekimoglu et al. (2002) and Denliand Deniz (2003) describe in their work the basic aspects of apply-ing the GCT. The null (H0) and alternative (Ha) hypotheses consid-ered in this test are given as:

H0 : E {d} = 0 (1)

Ha : E {d} ̸= 0 (2)

with

d = U2 − U1 (3)

where E is the mathematical expectation, d is the difference ofeach vector component of a point at two different times: U1 =(x1, y1, z1) and U2 = (x2, y2, z2).This test can be applied as follows (Neumann and Kutterer, 2006;Kapovic et al., 2006):

K = dT · Cd · dh · σ̂ 2

0d(4)

where K is the calculated factor that compares two times in theGCT,h is the rank of the covariancematrixCd ofd and σ̂ 2

0d is the aposteriori reference variance d, given by:

σ̂ 20d = V T

1 · P1 · V1 + V T2 · P2 · V2

ng(5)

where ng is the sum of the degrees of freedom, V is the residuevector and P is the weight of the observations at/over the time-lapse survey.In this work, bothng and σ̂ 2

0d were determined fromdata providedby the SIRGAS processing center.The statistic test follows the F distribution, where α is the signi -cance level.

P(K 6 FR,n,1−α | H0

)= 1 − α (6)

As an alternative hypothesis, we have K > FR,n,1−α .If the null hypothesis is rejected, then it can be assumed that therewas a position change or instability of the analyzed point over timeat a given α .

Unauthenticated | 68.107.139.75Download Date | 5/9/13 4:05 PM

Journal of Geodetic Science 15

Theuseof theF distribution to verify thehypotheses onCGT is dueto the fact that Eq. (4) follows non-centralF distribution, which is acontinuous probability distribution generalized of the F ordinarydistribution, frequently used for analysis of variance and to deter-mine if the variances of the two populations are the same.

2.4. Strain due to geodetic network

Turcotte and Schubert (2002) show that stress components can bede ned at any point of a given material. In order to illustrate thisprocedure, let’s consider a small planewith knowndimensions andoriented according to the cartesian coordinate system. In this sec-tion or plan, we consider a bi-dimensional stress state; therefore,no surface forces in the z-direction.The Finite Element Method was then used to determine the straincaused by the bi-dimensional stress state. According to Deniz andOzener (2010), this method can determine strain parameters inde-pendent of datum, using the distance relationship betweenpoints,or baselines, at two different times. Thus, the model does not con-sider the strain displacement of a given network, but only the de-formed ones. Strainwas determined by the Finite ElementMethodfor each at region formed, consisting of a at triangle de ned bythe Delaunay method.The linear expression to determine the resulting strain (ε) of a net-work baseline is given by:

ε = S ′ − SS (7)

where S is the planimetric distance between two network pointsat a given time 1 and S ′

is the planimetric distance between thesame points at time 2.Since the studied geodetic network was formed by properly ori-ented triangles, we used a general equation to determine the re-sulting bi-dimensional strain as a function of the adjusted param-eters (exxexy, eyy) and calculated azimuths (Az) for each deter-mined planimetric distance between two network points.

ε = exx cos2 Az + exy sin (2.Az) + eyy sin2 Az (8)

Equation 8 used to calculate strain was presented by Turcotte andSchubert (2002) and Deniz and Ozener (2010).Once strain parameters were determined, we calculated for eachplane formed by coordinate vector components, the maximum(E1) and minimum (E2) principal components of strain, togetherwith its orientation (β). It was also possible to determine the max-imum normal strain (Einter) and maximum shear (Eshear ).

E1 = 12

[(exx + eyy) +

√(exx − eyy

)2 + (2.exy)2]

(9)

E2 = 12

[(exx + eyy) −

√(exx − eyy

)2 + (2.exy)2]

(10)

β = arctan(

exy

E1 − exy

)(11)

Eshear = 12

(E1 − E2) (12)

Einter = 12

(E1 + E2) (13)

The same triangular networkswere also used todetermine altimet-ric strain (εz or ezz) according to the following equation:

εz = S ′z − Sz

Sz(14)

whereSz is thevertical distancebetweennetworkpoints at agiventime 1 and S ′

z is the vertical distance between the same pointsat time 2. The observations were adjusted by the Least-SquaresMethod (LSM) to determine the altimetric and planimetric geode-tic network strains. The parameters shown in the model used todetermine strain, Eq. (14), were adjusted by the LSM parametricmodel.

La = F (Xa) (15)

where La is the adjusted value vector and Xa is the adjusted pa-rameter vector.The covariance propagation law according to Gemael (1994) wasused to determine the accuracy of every calculation step, for agiven generalized model Y = F (X ), we have:

CY = DCX DT (16)

where CY is the variance-covariance matrix of Y ; D, the Jaco-bianmatrix formed by the partial derivatives andCX , the variance-covariance matrix of X .

2.5. Crust strain in the pre- and post-seismic periods

Based on the available seismological bulletin by the USGS (UnitedStates Geological Survey) for the study area during the 2000-2011period, we chose to investigate 23 important events ofmagnitudeshigher or equal to 5.8 Mw that hit at different depths(http://earthquake.usgs.gov/earthquakes/eqarchives/poster/byregion.php accessed on23/03/2012). Those events were chosen because they werereported with more details by USGS, allowing comparisons.For each chosen seismic event, the stability of each geodetic pointwas evaluated by the GCT. The objective was to reduce the studyarea to sites, where, statistically, the points were unstable. Theidenti ed triangular sites with at least one unstable vertex wereconsidered to be homogeneous regions whose strains were deter-mined.All calculations were performed by routines developed using thesoftware Matlab version 2010a according to the owchart shownin Fig. 2.

Unauthenticated | 68.107.139.75Download Date | 5/9/13 4:05 PM

Journal of Geodetic Science16

Figure 2. Flowchart of the routines used to calculate strains.

3. Results and Discussion

The owchart in Fig. 2 shows that each event was studied a twodifferent times, one week apart. The GCT (α = 10%) showed thatfrom the 23 seismic events chosen, only 7 had points of instabilitydetected (Table 2).

In order to associate the unstable points of the geodetic networkwith seismic events, the points distant from the hypocenters wererejected according to the CGT null hypothesis. Therefore, fromthe 7 chosen events, the 4 that were associated to unstable pointsin the geodetic network, were located in northern Chile, CostaRica, Off-shore Bio-Bio (Chile) and Baja (Mexico), and happened on06/13/2005, 01/08/2009, 02/27/2010 and 04/04/2010, respectively(Fig. 3).

The instability analysis detected displacements of the vector com-ponents of the points between 1 cm (point ETCG on 01/08/2009)and 3m (point CONZ on 02/27/2010) approximately, as shown inTable 2. It appears that the largest displacement occurred duringthe 8.8 magnitude earthquake, since the events on 10/09/2004,09/26/2005 and 08/12/2010, of magnitudes 6.9 Mw , 7.5 Mw and7.1Mw , respectively, were not considered in the strain analysis ac-cording the exclusion criterion.

Figure 3. Unstable geodetic points associated with seismic events.

The resulting strain was determined by the nite elementmethod,using the networks formed by the unstable points together withunstable or stable neighboring points connected to the rst by theDealunay method. The dimensionless unit used to represent thestrain rates, according to Deniz and Ozener (2010), was the micro-strain - µS .

The event on 06/13/2005 caused instability in the IQQE station.This station was connected to the neighboring points and bothplanimetric (Fig. 4a) and altimetric (Fig. 4b) strains that resulted,were calculated.

Figure 4a show that the AREQ, COPO and IQQE network locatedin the South American lithospheric plate had higher contractionplanimetric strain towards SW-NE in the direction of the Paci cOcean and consequently, toward theNazca lithospheric plate. Thiscontraction could be also detected by the networks formed byIQQE, COPO and UNSA, as well as IQQE, UNSA and CUIB. On theother hand, theAREQ, IQQE andCUIBnetwork extends towards thesamedirection. It is, probable, due to the regionand is thealtiplanosmall plate boundaries (Bird, 2003) and Sierras Pampeanas ”oro-gens” and also present different fault systems described by Heid-bach et al. (2009).

Figure 4b, unlike the planimetric analysis, display higher contrac-tion values for the IQQE, COPO and UNSA network. All otherformed networks show expansion.

The event on 01/08/2009 shows instability in the ETCG station.After the triangular networks were formed and the planimetric(Fig. 5a) and altimetric (Fig. 5b) resulting strains were calculated,the respective contraction and extension values were determined.

The points used to analyze this event are located in different litho-spheric regions. The point GLPS is in the Nazca plate, the point

Unauthenticated | 68.107.139.75Download Date | 5/9/13 4:05 PM

Journal of Geodetic Science 17

Table 2. Points of the SIRGAS-CON network that were considered unstable between pre- and post-seismic periods.

Seismic Events Points of Geodesic NetworkDate Location Depth Magnitude Geodetic

PointsDistance toHipocenter

Movements(Local Geodetic System)

(Km) (Mw) (Km) x (m) y (m) z (m)

10/09/2004 Nicaragua -35 6.9 OHI2 8493.684 -0.0154 0.0271 0.064306/13/2005 Northern

Chile-115 7.8 IQQE 104.385 -0.0341 -0.0448 -0.0244

09/26/2005 NorthernPeru

-127 7.5 OHI2 6556.179 0.0155 -0.0191 -0.0454

01/08/2009 CostaRica

-4.5 6.1 ETCG 22.489 -0.0083 0.0066 0.0200

02/27/2010 Offshore -35 8.8

CFAG 639.828 -0.0352 -0.0046 -0.0138

Bio-Bio

CONZ 114.505 -2.9777 -0.4451 -0.5163

Chile

LHCL 729.390 -0.0539 -0.0414 0.0100MZAC 495.136 -0.1065 -0.0237 -0.0442MZAE 527.059 -0.1015 -0.0347 -0.0394MZAS 445.600 -0.1958 -0.0779 -0.0299SANT 358.637 -0.2762 0.0058 -0.1085SRLP 820.967 -0.0494 -0.0289 0.0044UCOR 958.224 -0.0256 0.0005 -0.0054UNSJ 622.896 -0.0319 -0.0033 -0.0134VBCA 1059.043 -0.0249 -0.0204 0.0077

04/04/2010 Baja. Mexico -10 7.2 CONZ 8220.865 -0.0230 -0.0084 0.0032MEXI 58.418 0.0954 -0.1567 -0.1265

08/12/2010 Ecuador -211 7.1

IMBT 4010.076 0.0156 -0.0159 -0.0062SCCH 3683.549 0.0148 -0.0171 -0.0062SMAR 3840.254 0.0149 -0.0193 -0.0101SVIC 3563.048 0.0150 -0.0191 -0.0082

(a) (b)

Figure 4. a) Principal components of planimetric strain to the seismic event of 06/13/2005. b) Principal components of altimetric strain to theseismic event of 06/13/2005.

Unauthenticated | 68.107.139.75Download Date | 5/9/13 4:05 PM

Journal of Geodetic Science18

(a) (b)

Figure 5. a) Principal components of planimetric strain to the seismic event of 01/08/2009. b) Principal components of altimetric strain to theseismic event of 01/08/2009.

(a) (b)

Figure 6. a) Principal components of planimetric strain to the seismic event of 02/27/2010. b) Principal components of altimetric strain to theseismic event of 02/27/2010.

GCGT is in the North-American plate and the points MANA, ETCG,IGN1 and DAVI are in the Caribbean plate.

The network formed by the points GCGT, MANA and ETCG hadhigher planimetric strain based on principal components of strain.The contraction of the networks occurred predominantly towardsthe northeast, while expansion was towards the southeast. There-fore, it is possible to see that the Caribbean plate was compressedby the North-American and Nazca plates, towards the northeast,and it expanded towards the southeast in the direction of theSouth-American plate.

Table 2 shows that the 8.8 Mw earthquake, 35 km deep, that hap-pened on 02/27/2010, in Chile, caused instabilities in 11 geodeticpoints that, according to Fig. 6a and Fig. 6b, cover an area of thecontinental crust of the South-American lithospheric plate, fromthe Paci c to the Atlantic Ocean. Major strains were observed nearthe hypocenter, while minor ones were observed farther away, asmovements showed in Table 2 and strains plotted in Fig. 6a andFig. 6b.

According to Fig. 6a, the GLPS, ESQU and CONZ network locatedin the Nazca and South-American plates (Southern Sierras Pam-

Unauthenticated | 68.107.139.75Download Date | 5/9/13 4:05 PM

Journal of Geodetic Science 19

(a) (b)

Figure 7. a) Principal components of altimetric strain to the seismic event of 04/04/2010. b) Principal components of altimetric strain to the seismicevent of 04/04/2010.

peanas orogens) presents higher planimetric contraction values.The nding suggests that the Nazca plate is in subduction beneaththe South-American plate, which caused energy release, allowingthe point CONZ to move towards southwest. The CALL, CONZ andGLPS network, also with points in two different plates, expandedtowards southwest, and it was therefore, in uenced by the rststudied network.

All other formed networks located in the South-American platepresented planimetric extension strain, predominantly, in thenorth and southwest directions. This fact suggests that the pointsof the studied networks are growing farther apart and, conse-quently, the distention of the South-America continental crust atvarying degrees, according to the Fig. 6a.

The network altimetric strain occurred as contraction, and it washigher for the LHCL, CONZ and ESQU network, located in theSouth-American plate. Other networks changed between altimet-ric contraction and extension, as seen in Fig. 6b.

The event registered on 04/04/2010 was an earthquake of magni-tude 7.2 Mw , 10 km deep, with epicenter in Mexico. In this event,the geodesic point MEXI was considered unstable.

According to Fig. 7a, the GOLD,MEXI and PIE1 network showed thehighest plaminetric extension values. When compared to othernetworks, we can see that this extension was towards the south-east and contraction in the northeast direction.

All the studied networks are located in both North-American (theGorda California-Nevada orogens, Bird (2003)) and Paci c litho-spheric plates. Thus, based on Fig. 7a, it can be suggested thatthere was planimetric contraction between them and the area isin the boundary of regime of stress (Heidbach et al., 2009).

The altimetric strain analysis shows a big contraction in the MEXI,

HER2 and PIE1 network, as shown in Fig. 7b.

4. Conclusions

This study allowed to associate the unstable points of the SIRGAS-CON geodetic network with seismic events and to determine thestrain rates for pre- and post-seismic periods, while consideringeach triangular network as a homogeneous solid body.

Thedifferent strain values found for each seismic event analizedareassociated with different dimensions of the bodies formed by thenetwork, therefore, although small, they are possibility signi cantfor veri cation of the magnitudes and directions of stresses.

Strain calculation and result veri cation permitted analysis of theinteractions between the lithospheric plates from the view pointof contraction or extension of the points located in different plateswith the possibility to identify different regimes of stress and de-creasing the absence of information on regions.

Despite the association between seismic events and the geode-tic network strains, no correlation was found between the mag-nitude, epicentral distance and geodetic point instabilities. Thisnding can be con rmed by the exclusion of events located in

Nicaragua (6.9 Mw ), Peru (7.5 Mw ) and Ecuador (7.1 Mw ). On theother hand, it was found that greater magnitude events causedthe network points to dislocate more, as observed in the event on02/27/2010, in Chile (8.8 Mw ) in comparison with others. We cansuggest, based on the results presented, that the greater the depthless strain in the surface.

Finally, wecan say that the nite elementmethodapplied tobodiesformed by the Delaunay triangulation method is efficient for cal-culating strains of geodesic structures and for understanding theiterations of efforts that work in the lithosphere and can be seen

Unauthenticated | 68.107.139.75Download Date | 5/9/13 4:05 PM

Journal of Geodetic Science20

in the earth’s surface. Therefore, it is suggested that this method-ology is suitable to be applied to any area where observations areabundant geodesics.

Acknowledgements

The authors thank SIRGAS and the USGS for providing geodeticand seismological preliminary information used in the analyzes.This research is supported CNPq/INCT 573713/2008-1. We specialthank all technicians from UnB, USP and UFRN, for their efforts inthe eld work, maintenance of equipment, and preliminary read-ings of data. GSF and JFGM thanks CNPq for their PQ grants. RuthVidotti Kakogiannos for improvement of the English.

References

Bird P., 2003, An updated digital model of plate boundaries,Geochem. Geophys. Geosyst., 4, 3, 1-52.

Brunini C., Sánchez L., Drewes H., Costa S., Mackern V.,Martínez W., Seemuller W. and Silva A., 2012, Improved anal-ysis strategy and accessibility of the SIRGAS reference frame,Geodesy for Planet Earth, 136, 3-10.

Costa S.M.A., Silva A.L. and Vaz J.A., 2009, Avaliação doprocessamento da rede SIRGAS-CON pelo centro de análisesIBGE, Presented at the XXIV Reunión Cientí ca de la Aso-ciaciasión Argentina de Geofsicos y Geodestas, Mendoza,Argentina, April 13-17, 2009.

Deniz I. and Ozener H., 2010, Estimation of strain accu-mulation of densi cation network in northern Marmararegion, Turkey, Nat. Hazard. Earth Sys., 10, 2135-2143.

Denli H.H. and Deniz R., 2003, Global congruency testmethods for GPS networks, J Surv. Eng., 129, 3, 95-98.

Fernandes R.M.S., Miranda, J.M., Catalão J., Luis J.F., Bas-tos L. and Ambrosius B.A.C., 2002, Coseismic displacementsof the mw = 6.1, july 9, 1998, faial earthquake (Azores, northatlantic), Geophys. Res. Lett., 29, 16, 21-1-4.

Gemael C., 1994, Introdução ao Ajustamento de Obser-vações – Aplicações Geodésicas, Editora UFPR.

Heidbach O., Tingay M., Barth A., Reinecker J., Kurfe D. andMller B., 2009, The World Stress Map based on the databaserelease 2008, equatorial scale 1:46,000,000, Commission forthe Geological Map of the World.

Hekimoglu S., Demirel H. and Aydin C., 2002, Realiabilityof the conventional deformation analysis methods for vertival

networks, Presented at the XXII FIG International Congress,Washington, D.C. USA, April 19-26, 2002.

Hsu Y.-J., Yu S.-B. and Chen H.-Y., 2009, Coseismic and postseis-mic deformation associatedwith the 2003 chengkung, Taiwan,earthquake, Geophys. J. Int., 176, 2, 420-430.

Hudnut K.W., Bock Y, Cline M., Fang P., Feng Y., Freymueller J.,Ge X., Gross W.K., Jackson D., Kim M., King N.E., Langbein J.,Larsen S.C., Lisowski M., Shen Z.K., Svarc J. and Zhang J., 1994,Coseismic displacements of the 1992 landers earthquakesequence, Bull. Seismol. Soc. Am., 84, 3, 625-645.

Ishii M., Shearer P. M., Houston H. and Vidale J. E., 2005,Extent, duration and speed of the 2004 Sumatra-Andamanearthquake imaged by the hi-net array, Nature, 435:933-936.

Kapovic Z., Marendic A. and Paar R., 2006, Deformation analysisof the Holcim Ltda. Cement Factory Objects, Presented at theXXIII FIG International Congress, Munich, Germany, October8-13, 2006.

Monico J.F.G., 2008, Posicionamento pelo GNSS: Descrição,Fundamentos e Aplicações, 2nd Edition, Editora UNESP.

Neumann I. and Kutterer H., 2006, Congruency tests andoutlier detection in deformation analysis with respect toobservation imprecision, Presented at the 3rd IAG / 12th FIGSymposium, Baden, Austria, May 22-24, 2006.

Ruegg J.C., Rudloff A., Vigny C., Madariaga R., de ChabalierJ.B., Campos J., Kausel E., Barrientos S. and Dimitrov D., 2009,Interseismic strain accumulation measured by GPS in theseismic gap between Constitución and Concepción in Chile,Phys. Earth Planet. In., 175, 78-85.

Sánches L.W. and Seitz M., 2011, DGFI Report No87 - Re-cent activities of the IGS regional network associate analysiscentre for SIRGAS, Presented at the Report for the SIRGAS 2011General Meeting, Heredia, Costa Rica, August 8-10, 2011.

Satirapod C., Bamrungwong S., Vigny C. and Lee H.-K.,2010, Change of strain rate in Thailand after the 26 december2004 and 28 march 2005 earthquakes using GPS measure-ments, KSCE J. Civ. Eng., 14, 215-220.

Silva A.L., Costa S.M.A. and Vaz J.A., 2010, Deslocamentodas estações SIRGAS-CON em função do terremoto ocorridono Chile - uma abordagem do centro de processamentoSIRGAS – IBGE, Presenteed at the III Simpósio Brasileiro deCiências Geodésicas e Tecnologias da Geoinformação, Recife,Brazil, July 27-30, 2010.

Unauthenticated | 68.107.139.75Download Date | 5/9/13 4:05 PM

Journal of Geodetic Science 21

Turcotte D.L. and Schubert G., 2002, Geodynamics, 2ndEdition, Cambridge University Press.

Velasco M.S., Bennett R.A., Johnson R.A. and HreinsdóttirS., 2010, Subsurface fault geometries and crustal extension inthe eastern basin and range province, western U.S., Tectono-physics, 488, 1-4, 131-142.

Vigny C., Rudloff A., Ruegg J.-C., Madariaga R., Campos J.and Alvarez M., 2009, Upper plate deformation measured byGPS in the Coquimbo gap, Chile. Phys. Earth Planet. In., 175,86-95.

Wallace L.M., Stevens C., Silver E., McCaffrey R., LoratungW.,Hasiata S., Stanaway R., Curley R., Rosa R. and Taugaloidi J.,2004, GPS and seismological constraints on active tectonics

and arc-continent collision in Papua New Guinea: Implicationsfor mechanics of microplate rotations in a plate boundaryzone, J. Geophys. Res., 109, B5404, 1-16.

Yu S.B., Kuo L.C., Hsu Y.J., Su H.H., Liu C.C., Hou C.S., Lee J.F., Lai T.C., Liu C.C., Liu C.L., Tseng T.F., Tsai C.S. and Shin T.C.,2001, Preseismic deformation and coseismic displacementsassociated with the 1999 Chi-Chi, Taiwan, earthquake, Bull.Seismol. Soc. Am., 91, 5, 955-1012.

Zhang X., Jiang Z.-S., Wang Q., Wang S.-X., Cui D.-X. andZhang X.-L., 2005, Inversion for negative dislocation on elasticblock boundaries in the northeastern margin of Qinghai-Xizang block and prediction for strong earthquake llocation,Acta Seismol. Sin., 18, 666-677.

Unauthenticated | 68.107.139.75Download Date | 5/9/13 4:05 PM