Advances in Natural and Technological Hazards Research

Submarine Mass Movements and Their Consequences

Sebastian Krastel · Jan-Hinrich BehrmannDavid Völker · Michael StippChristian Berndt · Roger UrgelesJason Chaytor · Katrin HuhnMichael Strasser · Carl Bonnevie Harbitz Editors

6th International Symposium

Contents

Part I Physical Properties of Sediments

1 Weak Layers: Their Definition and Classificationfrom a Geotechnical Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Jacques Locat, Serge Leroueil, Ariane Locat, and Homa Lee

2 Field Measurements to Investigate Submerged Slope Failures . . . . . . . . 13Alexander van Duinen, Adam Bezuijen,Geeralt van den Ham, and Victor Hopman

3 Elemental Distribution and Microfabric CharacterizationAcross a Buried Slump Scar: New Insightson the Long-Term Development and Reactivationof Scar Surfaces from a Microscopic Perspective . . . . . . . . . . . . . . . . . . . . . . . 23Helen Eri Amsler, Eric Reusser, Kitty Milliken,and Michael Strasser

4 Evidence for Mass Transport Deposits at the IODPJFAST-Site in the Japan Trench . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Hiske G. Fink, Michael Strasser, Miriam Romer,Martin Kolling, Ken Ikehara, Toshiya Kanamatsu,Dominik Dinten, Arata Kioka, Toshiya Fujiwara,Kiichiro Kawamura, Shuichi Kodaira, Gerold Wefer,and R/V Sonne SO219A Cruise Participants

5 Preliminary Investigations of Rheological Propertiesof Busan Clays and Possible Implications for DebrisFlow Modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45Sueng Won Jeong, Sang-Nam Yoon, Sung-Sik Park,Gil Young Kim, Seong-Pil Kim, Jang-Jun Bahk,Nyeon-Keon Kang, Sang Hoon Lee, and Sung-Gyo Chung

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6 Utilizing Cone Penetration Tests for Landslide Evaluation . . . . . . . . . . . . 55M.E. Jorat, S. Kreiter, T. Morz, V. Moon, and W. de Lange

7 Geomechanical Characterization of SubmarineVolcano-Flank Sediments, Martinique, Lesser Antilles Arc . . . . . . . . . . . 73Sara Lafuerza, Anne Le Friant, Michael Manga,Georges Boudon, Benoit Villemant, Nicole Stroncik,Barry Voight, Matt Hornbach, Osamu Ishizuka,and The Expedition 340 Scientific Party

Part II Gas Hydrates and Role of Interstitial Fluidsin Submarine Slope Failure

8 Interrelationship Between Sediment Fabric, Pore VolumeVariations as Indicator for Pore Pressure Changes,and Sediment Shear Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85Lutz Torbahn and Katrin Huhn

9 Slope Instability of Glaciated Continental Margins:Constraints from Permeability-Compressibility Testsand Hydrogeological Modeling Off Storfjorden, NWBarents Sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95J. Llopart, R. Urgeles, A. Camerlenghi, R.G. Lucchi,B. De Mol, M. Rebesco, and M.T. Pedrosa

10 Baiyun Slide and Its Relation to Fluid Migration in theNorthern Slope of Southern China Sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105Wei Li, Shiguo Wu, Xiujuan Wang, Fang Zhao, Dawei Wang,Lijun Mi, and Qingping Li

11 Post-failure Processes on the Continental Slopeof the Central Nile Deep-Sea Fan: Interactions BetweenFluid Seepage, Sediment Deformation and Sediment-WaveConstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117Sebastien Migeon, Silvia Ceramicola, Daniel Praeg,Emmanuelle Ducassou, Alexandre Dano,Joao Marcelo Ketzer, Flore Mary, and Jean Mascle

12 Fluid Seepage in Relation to Seabed Deformationon the Central Nile Deep-Sea Fan, Part 1: Evidencefrom Sidescan Sonar Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129Alexandre Dano, Daniel Praeg, Sebastien Migeon,Jean-Marie Augustin, Silvia Ceramicola,Joao Marcelo Ketzer, Adolpho Herbert Augustin,Emmanuelle Ducassou, and Jean Mascle

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13 Fluid Seepage in Relation to Seabed Deformationon the Central Nile Deep-Sea Fan, Part 2: Evidencefrom Multibeam and Sidescan Imagery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141Daniel Praeg, Joao Marcelo Ketzer,Adolpho Herbert Augustin, Sebastien Migeon,Silvia Ceramicola, Alexandre Dano, Emmanuelle Ducassou,Stephanie Dupre, Jean Mascle, and Luiz Frederico Rodrigues

Part III Slope Stability and Risk Assessment

14 Advances in Offshore Seismic Slope Stability: A Case History . . . . . . . 153Omar Zanoli, Claudio Piatti, Lorenzo Zuccarino,and Eric J. Parker

15 Size-Frequency Relationship of Submarine Landslidesat Convergent Plate Margins: Implications for Hazardand Risk Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165Jan H. Behrmann, David Volker, Jacob Geersen,Rieka Harders, and Wilhelm Weinrebe

16 A Numerical Investigation of Sediment Destructuringas a Potential Globally Widespread Trigger for LargeSubmarine Landslides on Low Gradients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177Morelia Urlaub, Peter Talling, and Antonis Zervos

17 How Stable Is the Nice Slope? – An Analysis Basedon Strength and Cohesion from Ring Shear Experiments . . . . . . . . . . . . . 189Sylvia Stegmann and Achim Kopf

18 Regional Slope Stability Assessment Along the CaucasianShelf of the Black Sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201Vsevolod Yu. Ionov, Ernest V. Kalinin, Igor K. Fomenko,and Sergey G. Mironyuk

19 A Semi-empirical Method to Assess Flow-Slide Probability . . . . . . . . . . . 213Geeralt A. van den Ham, Maarten B. de Groot,and Dick R. Mastbergen

20 Submarine Slope Stability Assessment of the CentralMediterranean Continental Margin: The Gela Basin . . . . . . . . . . . . . . . . . . 225Fei Ai, Jannis Kuhlmann, Katrin Huhn, Michael Strasser,and Achim Kopf

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Part IV Monitoring, Observation and Repeated Surveysof Active Slope Failure Processes

21 The 1930 Landslide in Orkdalsfjorden: Morphologyand Failure Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239Jean-Sebastien L’Heureux, Oddvar Longva, Louise Hansen,and Maarten Vanneste

22 Imaging Active Mass-Wasting and Sediment Flowson a Fjord Delta, Squamish, British Columbia . . . . . . . . . . . . . . . . . . . . . . . . . 249John E. Hughes Clarke, Carlos R. Vidiera Marques,and Danar Pratomo

23 Coastal and Submarine Landslidesin the Tectonically-Active Tyrrhenian Calabrian Margin(Southern Italy): Examples and Geohazard Implications . . . . . . . . . . . . . 261Daniele Casalbore, Alessandro Bosman, Domenico Ridente,and Francesco Latino Chiocci

Part V Understanding Failure Processes from SubmarineLandslide Geomorphology

24 Recurrent Superficial Sediment Failure and DeepGravitational Deformation in a Pleistocene SlopeMarine Succession: The Poseidonia Slide (Salerno Bay,Tyrrhenian Sea) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273Francesca Budillon, Massimo Cesarano, Alessandro Conforti,Gerardo Pappone, Gabriella Di Martino, and Nicola Pelosi

25 Mass Wasting Features on the Submarine Flanksof Ventotene Volcanic Edifice (Tyrrhenian Sea, Italy) . . . . . . . . . . . . . . . . . . 285Daniele Casalbore, Alessandro Bosman, Eleonora Martorelli,Andrea Sposato, and Francesco Latino Chiocci

26 Submarine Mass-Movements Along the Slopesof the Active Ionian Continental Margins and TheirConsequences for Marine Geohazards (Mediterranean Sea) . . . . . . . . . . 295Silvia Ceramicola, Daniel Praeg, Marianne Coste, Edy Forlin,Andrea Cova, Ester Colizza, and Salvatore Critelli

27 Evidence for Submarine Landslides Offshore Mt. Etna, Italy . . . . . . . . 307Felix Gross, Sebastian Krastel, Francesco Latino Chiocci,Dominico Ridente, Jorg Bialas, Julia Schwab, Julio Beier,Deniz Cukur, and Daniel Winkelmann

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28 The Malta-Sicily Escarpment: Mass Movement Dynamicsin a Sediment-Undersupplied Margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317Aaron Micallef, Aggeliki Georgiopoulou, Timothy Le Bas,Joshu Mountjoy, Veerle Huvenne, and Claudio Lo Iacono

29 Submarine Mass Movements Along a Sediment StarvedMargin: The Menorca Channel (Balearic Islands –Western Mediterranean) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329Claudio Lo Iacono, Roger Urgeles, S. Polizzi, J. Grinyo,M. Druet, M. Agate, J.M. Gili, and J. Acosta

30 The Detection of Volcanic Debris Avalanches (VDAs)Along the Hellenic Volcanic Arc, Through MarineGeophysical Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339P. Nomikou, D. Papanikolaou, A. Tibaldi, S. Carey,I. Livanos, K.L.C. Bell, F.A. Pasquare, and G. Rousakis

31 Submarine Mass Movements and Trigger Mechanismsin Byfjorden, Western Norway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351Berit Oline Hjelstuen and Jo Brendryen

32 New Imaging of Submarine Landslides from the 1964Earthquake Near Whittier, Alaska, and a Comparisonto Failures in Other Alaskan Fjords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361Peter J. Haeussler, Tom Parsons, David P. Finlayson,Pat Hart, Jason D. Chaytor, Holly Ryan, Homa Lee,Keith Labay, Andrew Peterson, and Lee Liberty

33 A Geomorphological Analysis of the Veatch Slide ComplexOff Massachusetts, U.S.A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371Jacques Locat, Uri S. ten Brink, and Jason D. Chaytor

34 Characterization of Submarine Landslide ComplexesOffshore Costa Rica: An Evolutionary Model Relatedto Seamount Subduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381Rieka Harders, Cesar R. Ranero, and Wilhelm Weinrebe

35 Morphological Expression of Submarine Landslides in theAccretionary Prism of the Caribbean Continental Marginof Colombia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391Javier Idarraga-Garcıa and Carlos A. Vargas

36 Contrasting Development of the Latest Quaternary SlopeFailures and Mass-Transport Deposits in the UlleungBasin, East Sea (Japan Sea) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403Sang Hoon Lee, Jang-Jun Bahk, Han Joon Kim,Gil-Young Kim, Seong-Pil Kim, Sueng-Won Jeong,and Sung-Sik Park

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37 Seismic Characteristics and Distribution of Large ScaleMass Transport Deposits in the Qiongdongnan Basin,South China Sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413Dawei Wang, Shiguo Wu, Fuliang Lu, and George Spence

38 Modification of the Shape of Pacific Islands by SubmarineLandslides: Banaba, Nauru, and Niue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423Jens C. Kruger and Susanne M.L. Pohler

Part VI Interaction Between Ocean Circulation and MTDs

39 Submarine Landslides and Contourite Drifts Alongthe Pianosa Ridge (Corsica Trough, Mediterranean Sea) . . . . . . . . . . . . . . 435A. Cattaneo, G. Jouet, S. Charrier, E. Thereau,and V. Riboulot

40 Mass Transport Complexes from Contouriteand Shelf-Edge Deposits Along the South-WesternAdriatic Margin (Italy) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447Giacomo Dalla Valle, Elisabetta Campiani, Federica Foglini,Fabiano Gamberi, and Fabio Trincardi

41 Mass Wasting Along Atlantic Continental Margins: AComparison Between NW-Africa and the de la PlataRiver Region (Northern Argentina and Uruguay) . . . . . . . . . . . . . . . . . . . . . . 459S. Krastel, J. Lehr, D. Winkelmann, T. Schwenk,B. Preu, M. Strasser, R.B. Wynn, A. Georgiopoulou,and T.J.J. Hanebuth

42 Comparison of Mass Wasting Processes on the Slopesof the Rockall Trough, Northeast Atlantic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471Aggeliki Georgiopoulou, Sara Benetti, Patrick M. Shannon,Fabio Sacchetti, Peter D.W. Haughton, Laia Comas-Bru,and Sebastian Krastel

Part VII Landslide Generated Tsunamis

43 The State-of-the-Art Numerical Tools for ModelingLandslide Tsunamis: A Short Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483Mohammad Heidarzadeh, Sebastian Krastel,and Ahmet C. Yalciner

44 Modeling Submarine Landslide-Generated Waves in LakeOhrid, Macedonia/Albania . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497Katja Lindhorst, Sebastian Krastel, Cord Papenberg,and Mohammed Heidarzadeh

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45 Modeling Potential Tsunami Generationby the BIG’95 Landslide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507Finn Løvholt, Carl B. Harbitz, Maarten Vanneste,Fabio V. De Blasio, Roger Urgeles, Olaia Iglesias,Miquel Canals, Galderic Lastras, Geir Pedersen,and Sylfest Glimsdal

46 Modeling of Potential Landslide Tsunami Hazards OffWestern Thailand (Andaman Sea) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517Julia Schwab, Sebastian Krastel, Mohammad Heidarzadeh,and Sascha Brune

47 Morphology of Australia’s Eastern Continental Slopeand Related Tsunami Hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529Samantha Clarke, Thomas Hubble, David Airey, Phyllis Yu,Ron Boyd, John Keene, Neville Exon, James Gardner,Steven Ward, and Shipboard Party SS12/2008

48 The Tsunami Generation Potential of Shovel and BulliSlides in the Continental Margin SE Australia . . . . . . . . . . . . . . . . . . . . . . . . . . 539Asrarur Rahman Talukder and David Volker

Part VIII Long-Term Record of Submarine Landslides andMTD Paleoseismology

49 Along-Strike Migration of Intermittent Submarine SlopeFailures at Subduction Margins: Geological Evidencefrom the Chikura Group, Central Japan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551Yuzuru Yamamoto and Shunsuke Kawakami

50 Quaternary Mass-Transport Depositson the North-Eastern Alboran Seamounts(SW Mediterranean Sea) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561B. Alonso, G. Ercilla, M. Garcia, J.T. Vazquez, C. Juan,D. Casas, F. Estrada, E. D´Acremont, Ch. Gorini,B. El Moumni, and M. Farran

51 Searching for the Record of Historical Earthquakes,Floods and Anthropogenic Activities in the VarSedimentary Ridge (NW Mediterranean) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 571V. Hassoun, J. Martın, S. Migeon, C. Larroque, A. Cattaneo,M. Eriksson, J.A. Sanchez-Cabeza, B. Mercier de Lepinay,L. Liong Wee Kwong, I. Levy, L.-E. Heimburger,and J.-C. Miquel

52 Integrated Stratigraphic and Morphological Investigationof the Twin Slide Complex Offshore Southern Sicily . . . . . . . . . . . . . . . . . . . 583J. Kuhlmann, A. Asioli, M. Strasser, F. Trincardi,and K. Huhn

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53 Mass Transport Deposits Periodicity Related to GlacialCycles and Marine-Lacustrine Transitions on a PondedBasin of the Sea of Marmara (Turkey) Over the Last 500 ka . . . . . . . . . 595C. Grall, P. Henry, G.K. Westbrook, M.N. Cagatay,Y. Thomas, B. Marsset, D. Borschneck, H. Saritas, G. Cifci,and L. Geli

54 Instability of Oceanic Volcanic Edifices: Examplesof Sector Collapse, Debris Avalanches, and Debris Flowsfrom Gran Canaria (Canary Islands) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605Hans-Ulrich Schmincke and Mari Sumita

55 Slope Failures and Timing of Turbidity Flows Northof Puerto Rico . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617Jason D. Chaytor and Uri S. ten Brink

56 Age Estimation of Submarine Landslides in the La AgujaSubmarine Canyon, Northwestern Colombia . . . . . . . . . . . . . . . . . . . . . . . . . . . 629Carlos A. Vargas and Javier Idarraga-Garcıa

57 Deep-Sea Turbidite Evidence on the Recurrence of LargeEarthquakes Off Shakotan Peninsula, Northeastern Japan Sea . . . . . . 639Ken Ikehara, Takuya Itaki, Taqumi TuZino,and Koichi Hoyanagi

58 Characteristics of Magnetic Fabrics in Mass TransportDeposits in the Nankai Trough Trench Slope, Japan . . . . . . . . . . . . . . . . . . . 649Yujin Kitamura, Michael Strasser, Beth Novak,Toshiya Kanamatsu, Kiichiro Kawamura, and Xixi Zhao

Part IX Outcrops of Ancient Submarine Landslides

59 New Concepts on Mass Wasting Phenomena at Passiveand Active Margins of the Alpine Tethys: FamousClassical Outcrops in the Berchtesgaden – Salzburg AlpsRevisited. Part A: Jurassic Slide/Debrite ComplexesTriggered by Syn-Sedimentary Block Faulting. . . . . . . . . . . . . . . . . . . . . . . . . . 661Rudiger Henrich, Karl-Heinz Baumann, and Torsten Bickert

60 New Concepts on Mass Wasting Phenomena at Passiveand Active Margins of the Alpine Tethys: FamousClassical Outcrops in the Berchtesgaden – Salzburg AlpsRevisited. Part B: Stacking Patterns of Slide/DebriteComplexes in an Active Lower Cretaceous ForelandWedge-Top Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 675Rudiger Henrich, Karl-Heinz Baumann, and Torsten Bickert

Chapter 20Submarine Slope Stability Assessmentof the Central Mediterranean ContinentalMargin: The Gela Basin

Fei Ai, Jannis Kuhlmann, Katrin Huhn, Michael Strasser, and Achim Kopf

Abstract This study investigates slope stability for a relatively small scale(5.7 km2, 0.6 km3), 8 kyr old landslide named Northern Twin Slide (NTS) atthe slope of the Gela Basin in the Sicily Channel (central Mediterranean). The NTSis characterized by two prominent failure scars, forming two morphological stepsof 110 and 70 m height. Geotechnical data from a drill core upslope the failurescar (GeoB14403) recovered sediments down to �52 m below seafloor (mbsf).The deposits show low over consolidation ratio (OCR D 0.24–0.4) and low internalfriction angle (20–22ı) around 28–45 mbsf, which suggests this mechanicallyweak interval may act as potential location of instability in a future failure event.Oedometer tests attest the sediments are highly under consolidated and the averageoverpressure ratio (�*) is �0.7. Slope stability analyses carried out for differentscenarios indicate that the slope is stable both under static undrained and drainedconditions. A relatively small horizontal acceleration of 0.03–0.08 g induced by anearthquake may be sufficient to cause failure. We propose that moderate seismictriggers may have been responsible for the twin slide formation and could alsocause mass wasting in the future.

Keywords Slope stability • Submarine landslide • Geotechnical characteristics •Central Mediterranean

F. Ai (�) • J. Kuhlmann • K. Huhn • A. KopfMARUM-Center for Marine Environmental Sciences, and Faculty of Geosciences, Universityof Bremen, Leobener Straße, 28359 Bremen, Germanye-mail: aifei@uni-bremen.de; jkuhlmann@marum.de; khuhn@uni-bremen.de;akopf@uni-bremen.de

M. StrasserGeological Institute, ETH Zurich, Sonneggstrasse 5, 8092 Zurich, Switzerlande-mail: strasser@erdw.ethz.ch

S. Krastel et al. (eds.), Submarine Mass Movements and Their Consequences, Advancesin Natural and Technological Hazards Research 37, DOI 10.1007/978-3-319-00972-8 20,© Springer International Publishing Switzerland 2014

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226 F. Ai et al.

20.1 Introduction

Submarine landslides are ubiquitous on continental margins. Overpressure near theseafloor plays a significant role in the occurrence of submarine landslides (Flemingset al. 2008). Seismic activity is considered as an important triggering mechanism ofsubmarine landslides (Masson et al. 2006). It is therefore important to evaluate theeffects of overpressure as a preconditioning factor and seismic shaking as triggeringmechanism for submarine slope instability in earthquake-prone regions.

The study area is located between 200 and 800 m water depth along theeastern margin of the Gela Basin of the Sicily Channel, central Mediterranean.The continental slope has a general gradient (approx. 3ı) and steep slide headscarps (up to 32ı in places) (Fig. 20.1a). Two recent slides (termed Northern TwinSlide and Southern Twin Slide) show subrounded scars on the upper slope and arecharacterized by bathymetric bulges at the base of the slope (Minisini et al. 2007).These landslides are described as multiple failures likely controlled by specificstratigraphic surfaces acting as glide planes (Minisini and Trincardi 2009; Trincardiand Argnani 1990).

In order to provide a possibility to assess future slope instabilities due to over-pressure and seismic shaking, undrained and drained infinite slope stability modelsare introduced to model slope stability under both static and pseudostatic conditions.

20.2 Geological Setting

The Gela Basin is the most recent (Plio-Quaternary) foredeep of the Maghrebianfold-and-thrust belt (Argnani et al. 1986). The extensional basin originated inthe late Miocene to early Pliocene with the emplacement of the Gela nappe,which lasted until the early Pleistocene (Grasso 1993). Sequence stratigraphicinterpretation on the shelf and upper slope area on the Gela Basin (Minisini andTrincardi 2009; Kuhlmann et al. 2013) identify, from top to bottom (Fig. 20.1b): (I)deposits resting on top of erosive unconformity ES1, (II) a progradational wedgepinching out towards NE and (III) deposits beneath sequence boundary SB1. Ingeneral, the studied northern slope of the Gela Basin shows high sedimentationrates of 85–250 mm/kyr area result of abundant supply of fine-grained material andtectonic subsidence (Emeis et al. 1996).

The NTS is characterized by two prominent failure scars forming two morpho-logical steps of 110 and 70 m height (Fig. 20.1b). The slope angle of the slideheadwall is around 16ı, while the surfaces of the displaced masses dip at 1.5–4.5ı(Minisini et al. 2007). The accumulation area of the NTS is characterized by amorphologic bulge at the seafloor which extends 7 km downslope and 1.5 km inwidth. The source area of the NTS is 5.7 km2 and the average height of the failuresection is approx. 100 m. The runout of the NTS is 11.7 km (Minisini et al. 2007).

20 Submarine Slope Stability Assessment of the Central Mediterranean. . . 227

Fig. 20.1 (a) Overview map showing the morphology of the Twin Slides in the Gela Basinoffshore Sicily (Italy). Black dot indicates the location of core GeoB14403. Red dashed linesindicate the scarps of the Twin Slides. Black lines indicate the locations of parasound profilespresented in (b). (b) Parasound sub-bottom profile crossing the NTS. Red rectangle shows thelocation of the core GeoB14403. Green dashed lines indicate the Erosion surface 1 (ES1) and thesequence boundary1 (SB1). Red dashed lines indicate the boundaries of different Marine OxygenIsotope Stages (MIS) (Minisini et al. 2007; Kuhlmann et al. 2013). Black dashed line indicates theslip surface of the upper retrogressive landslide

228 F. Ai et al.

20.3 Material and Methods

20.3.1 Shipboard and Laboratory Analysis

The principal data set for this study is based on a MeBo (MARUM seafloor drillrig) core and a co-located gravity short core, both acquired during Cruise MSM15/3in 2010. A 51.9 m-long succession from the undisturbed slope apron upslope theNTS scar was recovered. Visual core description was carried out on board shortlyafter core recovery on the split core. Discrete samples were taken on board tomeasure water content and bulk density using oven drying method and pycnometer(Blum 1997). Undrained shear strength (Su) was estimated using a MennerichGeotechnik (Germany) vane shear apparatus (Blum 1997) and Wykeham Farrancecone penetrometer (Wood 1985).

Laboratory experiments consisted of grain size distribution analysis using aBeckman Coulter LS 13320 particle size analyzer and Atterberg limits using theCasagrande apparatus and rolling thread method (Casagrande 1932). Consolidationtests were performed using uniaxial incremental loading oedometer system (ASTM2004a), with permeability being estimated from the consolidation test results (Lamband Whitman 1969). The drained sediment strength parameters, cohesion (c0) andinternal friction angle (�0), were determined using drained direct shear tests (ASTM2004b).

20.3.2 Overpressure Estimation

Effective stress is an important parameter for slope stability analysis. Overpressureimpacts the effective stress as seen in Terzaghi et al. (1996). Overpressure (�u) isdefined as fluid pressure (u) in excess of hydrostatic equilibrium (u0) (Dugan andSheahan 2012). The Terzaghi’s effective stress relationship is:

� 0v D �v � u D �v � .u0 C �u/ D .b � w/ gz � �u

D . � w/ z � �u D 0z � �u(20.1)

Where � 0v is vertical effective stress, �v is total overburden stress, b is bulk density

(assuming constant), w is density of water (assuming constant), is unit weight, w is unit weight of water, 0 is buoyant weight, z is overburden depth, and g is theacceleration due to gravity.

Preconsolidation stress (� 0pc) interpreted from consolidation test is an approach

to evaluate overpressure (Casagrande 1936):

�u D � 0vh � � 0

pc (20.2)

20 Submarine Slope Stability Assessment of the Central Mediterranean. . . 229

Where � 0vh is vertical effective stress for hydrostatic conditions (� 0

vh D 0z). Theoverpressure was used to perform back analysis of slope stability under drainedconditions.

20.3.3 Slope Stability Analysis

The infinite slope stability analysis is used to calculate the factor of safety (FS). Inthe infinite slope approximation FS � 1 represents stability and FS < 1 representsinstability. For static conditions the FS calculation after Morgenstern (1967) andLøseth (1999) follows:

FS D Su

0z sin � cos �.Undrained/ (20.3)

FS D c0 C 0z�cos2 � � ��� tan �0

0z sin � cos �.Drained/ (20.4)

Where � is slope angle (also assumed angle for slip surface) and �* is over-pressure ratio (�� D �u

ı� 0

vh ). The evaluation of slope stability under earthquakeloading is commonly based on pseudostatic analysis (ten Brink et al. 2009;Morgenstern 1967). The overpressure that may be generated during an earthquake isnot taken into account for the slope stability analysis. The seismic response includedin the FS calculation is the integrated horizontal ground acceleration kg (where k ishorizontal acceleration coefficient and g is the acceleration due to gravity), which isassumed to be applied over a time period long enough for the induced shear stresscan to be considered constant.

FS D Su

0z Œsin � cos � C k . = 0 / cos2��.Undrained/ (20.5)

FS D c0 C 0z�cos2 � � �� tan �0

0z Œsin � cos � C k . = 0 / cos2��.Drained/ (20.6)

The aim of the stability analysis is to estimate the static FS of the slope and theminimum seismic acceleration required to trigger a slope failure under undrainedand drained conditions, respectively.

20.4 Results

20.4.1 Physical and Geotechnical Properties

The physical properties and geotechnical results are presented in Fig. 20.2. Thedominant lithology is homogeneous silty clay to clayey silt with a narrow range

230 F. Ai et al.

Fig. 20.2 Lithological, physical properties and geotechnical properties profile of core GeoB14403for slope stability assessment

of particle sizes. The sediment’s plastic limit is �28 %, while the liquid limitranges from 55 to 74 %. Natural water content is close to the liquid limit andgradually decreases with depth, while bulk density gradually increases with depth.Undrained shear strength values range from a few kPa near the seafloor to �50 kPaat depth, where the pocket penetrometer generally shows slightly higher valuesthan vane shear. The undrained shear strength-depth relation obtained from pocketpenetrometer tests is: Su D 0.6z C 37 (kPa, R2 D 0.64). The sediment appears tobe under consolidated as inferred from low ratios between the undrained shearstrength and vertical effective stress at static condition (Su

ı� 0

vh � 0:1) (Locat andLee 2002).

Consolidation tests indicate sediments are slightly under consolidated(OCR D � 0

pc /� 0vh D 0.76 at 4.08 mbsf)at shallow subsurface depth and become

strongly under consolidated deeper downhole(OCR D 0.23 at 49 mbsf).Overpressures estimated from consolidation test results using Eq. 20.2 indicatethat overpressure increases with depth and �* ranges from 0.24 to 0.77. Draineddirect shear tests indicate that sediments from 28 to 45 mbsf have somewhat lowerangle of internal friction (approx. 20ı) compared to one sample from shallow depth(approx. 30ı). Values of the effective cohesion intercept (c0), range from 0 to 30 kPafor granular to clay-rich sediments.

20 Submarine Slope Stability Assessment of the Central Mediterranean. . . 231

Table 20.1 Parameters used for slope stability calculations (Data derived from Fig. 20.2)

Static or variable/value (in different scenarios)

Input parameters Undrained static Drained staticUndrainedseismic

Drainedseismic

Undrained shear strength,Su(kPa)

Static/0.6z C 3.7 Static/33.7

Depth of the failure surface,z (m)

Variable/10–100 Static/50

Slope angle, ™ (ı) Variable/1–5.5Cohesion, c0 (kPa) – Static/23.5 – Static/23.5Internal friction angle,

·0 (ı)– Static/21 – Static/21

Overpressure ratio, œ* – Variable/0.4–1.0 – Static/0.7Unit weight, ” (kN/m2) – – Static/16.4Horizontal acceleration

coefficient, k– – Variable/0–0.09

Buoyant weight, ”0 (kN/m2) 6.6Gravitational acceleration,

g (m/s2)9.81

FS/k 1.9/0 3.6/0 1/0.02 1/0.053

Fig. 20.3 Slope stability analysis under undrained (a) and drained (b) conditions for the NTS.Contour plots indicate FS values. Dashed white lines indicate current mean values of theparameters in the NTS

20.4.2 Slope Stability Analysis

Factor of safeties for four different cases were calculated using Eqs. 20.3, 20.4, 20.5,and 20.6 with two parameters changing within a certain range and other parameterskeeping at constant value (Table 20.1 and Figs. 20.3 and 20.4). According to

232 F. Ai et al.

Fig. 20.4 Back-calculation of pseudostatic horizontal acceleration ratio showing FS as a functionof slope angle and pseudostatic horizontal acceleration ratio under undrained (a) and drained (b)conditions for the NTS. Contour plots indicate FS values. Dashed white lines indicate the valueof pseudostatic horizontal acceleration required to trigger slope failure (FS D 1) at current meanvalue of the slope angle

the parameters of current situation, the factor of safeties of static undrained anddrained cases can be constrained (Fig. 20.3). Horizontal acceleration coefficientsin earthquake undrained and drained cases were back-calculated using Eqs. 20.5and 20.6 while FS D 1. The slope appears to be presently stable both under staticundrained and drained conditions. The depth of the failure surface shows lessinfluence on FS compared to slope angle in the undrained slope stability analysis.Overpressure ratios �* � 0.93 are required to fail a drained slope at an angle of 5.5ı.Pseudo-static analysis indicates that slope is vulnerable in undrained earthquakecase. Horizontal acceleration coefficient k D 0.02 is need to trigger slope failurein undrained earthquake case, while higher horizontal acceleration coefficient(k D 0.053) is required to trigger slope failure (FS D 1) at current mean values ofthe slope angle (3ı) in drained earthquake case.

20.5 Discussion

20.5.1 Preconditioning Factors

Generally factors such as high sedimentation rate, slope steepening and the presenceof intrinsically weak layer scan greatly reduce the factor of safety of slopeunder static loading conditions. High sedimentation (�m/kyr) of low permeabilitysediments (permeability �10�16 m2) can generate overpressure, a condition known

20 Submarine Slope Stability Assessment of the Central Mediterranean. . . 233

as under consolidated (Dugan and Sheahan 2012). Undrained shear tests and consol-idation tests presented here suggest the sediments are strongly under consolidated(OCR D 0.27–0.77). The state of overpressure in the Gela basin most likely resultsfrom deposition of fine-grained sediments with high sedimentation rates. Basedon seismostratigraphic interpretation and shallow cores a high sedimentation rate(0.3–0.6 m/kyr) was proposed since the Last Glacial Maximum at 18–24 kyr B.P.(Minisini and Trincardi 2009). Kuhlmann et al. (2013) estimate the sedimentationrate was �0.5 m/kyr during MIS 1 and �1 m/kyr during MIS 3 according toresults from the MeBo core recovered in the undisturbed slope apron of the NTS.Based on our oedometer experiments, the coefficient of permeability of sedimentis on the order of 10�10 m/s (permeability �10�16 m2). Such a low permeabilitymay inhibit fluid seepage and thereby induce the overpressure buildup (Dugan andSheahan 2012).

The slope stability analysis suggests the slope angle has a larger influence onthe FS than on depth of failure plane. Since FS decreases with increasing slopeangle, one possible mechanism for failure could be rapid wedge-shaped sedimentaccumulation during sea level low stand (Minisini et al. 2007) or bottom currentsleading to net erosion and undercutting the toe of slope (Bennett and Nelsen 1983).Both mechanisms have been hypothesized to occur in the study area (Minisini et al.2007; Verdicchio and Trincardi 2008). Based on low internal friction angle derivedfrom direct shear test, sediments from 28 to 45 mbsf appear to be weaker, potentiallyforming a preferential slip plane for future slope failure. Slope stability analysisfurther suggests the slope is stable in static conditions. To reach FS D 1 or lower,an overpressure ratio of 0.93 at slope angle of 5.5ı would be required, which is notobserved at present. Hence additional triggers are needed to generate slope failure.

20.5.2 Triggering Factors

Pseudostatic slope stability analysis suggests that pseudostatic horizontal accelera-tion in the order of 0.02–0.053 g is required to fail the slope (FS D 1) in undrainedas well as drained conditions. Strasser et al. (2011), based on the principles by Seedand Idriss (1971) and Seed (1979), suggested that the pseudostatic horizontal accel-eration only represent �65 % of the effective earthquake peak ground acceleration(PGA D 0.03–0.08 g). In order to explore plausible scenarios for earthquake events,which might induce seismic shaking in this intensity range and thus could triggerslope failure of the NTS, PGA is estimated using empirical attenuation equationsafter Bindi et al. (2011) that depend on the combination of magnitude and sourcedistance of earthquake (Fig. 20.5).

The Sicily channel show slow seismic activity (Fig. 20.5a). Over the last40 year, only small earthquakes occurred, which are too low to trigger instabilities(Fig. 20.5b). The attenuation relationship combined with the critical thresholdcondition for instability, as revealed from our analysis, indicates that moderateearthquakes with magnitudes M D 4.0–4.8 near or at the location of the study area,

234 F. Ai et al.

Fig. 20.5 (a) Earthquake record of the Sicily channel since 1970 (USGS database). Dashed blackcircles indicate the distance to the study area. Red circles indicate magnitude levels of earthquakes.(b) PGA estimation using empirical attenuation equations after Bindi et al. (2011) that depends oncombination of magnitude and source distance of earthquake. Contour plots indicate the PGA. Redlines indicate the PGA values are required to trigger slope failure. Dashed white lines indicate thelargest and closest earthquake in the study area during last 40 year

or strong (M D 7), far-field events in epicentral distance <20–80 km are required totrigger the slope failure. Past landslide occurrence in the study area indicates thatover a longer time scale, larger magnitude earthquakes than those recorded duringthe instrumental period may have occurred. We propose that moderate seismictriggers may have been responsible for NTS formation and could also cause masswasting in the future.

20.6 Conclusions

In summary, we have demonstrated geotechnical properties of sediments and slopestability analysis of the Gela Basin. Strongly under consolidation of the sedimentsin the study area are mainly attributed to rapid sedimentation in fine sediments.Despite of the high overpressure presented in the sediments, the stability analysissuggests the slope is stable under static conditions. Slope failure may be triggered bymoderate earthquake (M4.0–M4.8) in the study area, or even strong events if fartheraway. Additional studies of in-situ pore pressure measurement and pore pressurechange during the seismic loading are needed in order to further investigate thedynamic response and better assess the slope stability.

Acknowledgments We thank the captain and crew of the RV Meteor for their support during thecruise MSM 15/3. Matthias Lange is thanked for outstanding technical assistance with the geotech-nical laboratory devices. This study has been funded through DFG-Research Center/Cluster ofExcellence “The Ocean in the Earth System”. We also like thank reviewers Brandon Dugan andVasilios Lykousis for their constructive remarks.

20 Submarine Slope Stability Assessment of the Central Mediterranean. . . 235

References

Argnani A, Cornini S, Torelli L, Zitellini N (1986) Neogene-quaternary foredeep system in thestrait of Sicily. Mem Soc Geol Italy 36:123–130

ASTM (2004a) Standard test methods for one-dimensional consolidation properties of soils usingincremental loading (Standard D2435-04). ASTM International, West Conshohocken, p 10

ASTM (2004b) Standard test method for direct shear test of soils under consolidated drainedconditions (Standard D3080-04). ASTM International, West Conshohocken, p 7

Bennett RH, Nelsen TA (1983) Seafloor characteristics and dynamics affecting geotechnicalproperties at shelf breaks. SEPM Spec Publ 33:333–355

Bindi D, Pacor F, Luzi L, Puglia R, Massa M, Ameri G, Paolucci R (2011) Ground motionprediction equations derived from the Italian strong motion database. Bull Earthq Eng9(6):1899–1920. doi:10.1007/s10518-011-9313-z

Blum P (1997) Physical properties handbook: a guide to the shipboard measurement of physicalproperties of deep-sea cores. ODP Tech Notes 26:118

Casagrande A (1932) Research on the Atterberg limits of soil. Public Roads 13(8):121–136Casagrande A (1936) The determination of the pre-consolidation load and its practical signifi-

cance. In: Proceedings of the 1st international conference of soil mechanics and foundationengineering 3, pp 60–64

Dugan B, Sheahan TC (2012) Offshore sediment overpressures of passive margins: mechanisms,measurement, and models. Rev Geophys 50(3), RG3001. doi:10.1029/2011rg000379

Emeis K, Robertson A, Richter C (1996) Site 963. Proceedings ODP, Initial Report 160, pp 55–84Flemings PB, Long H, Dugan B, Germaine J, John CM, Behrmann JH, Sawyer D, Scientists

IE (2008) Pore pressure penetrometers document high overpressure near the seafloor wheremultiple submarine landslides have occurred on the continental slope, offshore Louisiana, Gulfof Mexico. Earth Planet Sci Lett 269(3–4):309–325. doi:10.1016/j.epsl.2007.12.005

Grasso M (1993) Pleistocene structures along the Ionian side of the Hyblean Plateau (SE Sicily):implications for the tectonic evolution of the Malta Escarpment. In: Max MD, Colantoni P (eds)Geological development of the Sicilian-Tunisian platform, vol 58, UNESCO report marinescience. UNESCO, Paris, pp 49–54

Kuhlmann J, Asioli A, Strasser M, Trincardi F, Huhn F (2013) Integrated stratigraphic andmorphological investigation of the Twin Slide complex offshore southern Sicily. In: KrastelS et al (eds) Submarine mass movements and their consequences. Springer, Heidelberg

Lamb TW, Whitman RV (1969) Soil mechanics. Massachusetts Institute of Technology, Cam-bridge, MA

Locat J, Lee HJ (2002) Submarine landslides: advances and challenges. Can Geotech J39(1):193–212. doi:10.1139/t01-089

Løseth TM (1999) Submarine massflow sedimentation: computer modelling and basin-fill stratig-raphy. Springer, New York

Masson DG, Harbitz CB, Wynn RB, Pedersen G, Løvholt F (2006) Submarine landslides:processes, triggers and hazard prediction. Philos Trans R Soc A Math Phys Eng Sci364(1845):2009–2039. doi:10.1098/rsta.2006.1810

Minisini D, Trincardi F (2009) Frequent failure of the continental slope: the Gela Basin (SicilyChannel). J Geophys Res 114(F3), F03014. doi:10.1029/2008jf001037

Minisini D, Trincardi F, Asioli A, Canu M, Foglini F (2007) Morphologic variability of exposedmass-transport deposits on the eastern slope of Gela Basin (Sicily channel). Basin Res19(2):217–240. doi:10.1111/j.1365-2117.2007.00324.x

Morgenstern NR (1967) Submarine slumping and the initiation of turbidity currents. In: RichardsAF (eds) Marine Geotechnique. University of Illinois Press, Urbana, pp 189–210

Seed HB (1979) Considerations in earthquake-resistant design of earth and rock-fill dams.Geotechniques 29:215–263

Seed HB, Idriss IM (1971) Simplified procedure for evaluating soil liquefaction potential. J SoilMech Found Div Proc Am Soc Civil Eng 97:1249–1273

236 F. Ai et al.

Strasser M, Hilbe M, Anselmetti F (2011) Mapping basin-wide subaquatic slope failuresusceptibility as a tool to assess regional seismic and tsunami hazards. Mar Geophys Res32:331–347. doi:10.1007/s11001-010-9100-2

ten Brink US, Lee HJ, Geist EL, Twichell D (2009) Assessment of tsunami hazard to the U.S.East Coast using relationships between submarine landslides and earthquakes. Mar Geol264(1–2):65–73. doi:http://dx.doi.org/10.1016/j.margeo.2008.05.011

Terzaghi K, Peck RB, Mesri G (1996) Soil mechanics in engineering practice. Wiley Inter Science,New York

Trincardi F, Argnani A (1990) Gela submarine slide: a major basin-wide event in the plio-quaternary foredeep of Sicily. Geo-Mar Lett 10(1):13–21. doi:10.1007/bf02431017

Verdicchio G, Trincardi F (2008) Mediterranean shelf-edge muddy contourites: examples from theGela and South Adriatic basins. Geo-Mar Lett 28(3):137–151. doi:10.1007/s00367-007-0096-9

Wood DM (1985) Some fall-cone tests. Geotechnique 38:64–68