Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
The 2004 Aceh and 2005 Nias events are the two greatest earthquakes of the past 40 years with a total rupture of 1700 km long and a coseismic slip reaching up to 25 m. These two earthquakes have caused large stress perturbations which significantly altered seismic activity in the Sumatra-Andaman region. Using both detailed mapping of failure planes and various slip distributions, we calculate this stress change along the Sumatra-Andaman-Sagaing fault system from central Sumatra to southern Myanmar. The static Coulomb stress change Delta CFF and the observed seismic activity are in very good agreement with a Coulomb index similar to 20% greater than the one obtained for random events. Compared to previous studies, this high Coulomb Index confirms two important issues on the use of static stress change criterion: unsuited to study near-field aftershocks and only relevant for aftershocks analysis on large and mature faults at a time scale of several months. The calculated Delta CFF distribution suggests that the 2004 and 2005 earthquakes inhibit failure on the North Andaman rift and on the Sagaing fault, while failure is encouraged along the transform Andaman zone, the central Andaman rift, the West Andaman fault, the Sumatra fault system, and the offshore thrust faults west of Sumatra Island. The maximum value of similar to 15-20 bar (1.5-2 MPa) for Delta CFF is reached in the northern part of the Sumatra fault system. This high value together with the lack of major earthquake in the last 170 years result in a high seismic hazard for this region. Our results are also consistent with temporal evolution of both earthquakes' location and focal mechanism prior to and after the events. In particular, we explain the occurrence and the mechanism of seismic swarms observed in the central Andaman rift and along the west Andaman fault. Finally, our calculations reveal that the seismicity in the Andaman rift zone can only be explained if mu' > 0.5. This result leads to two end-member models: one with a constant and high fault friction and one with spatial variations, for which friction may depend on either the nature of the lithosphere (oceanic versus continental) or the fault type.
ISSN: 1525-2027

hal-00456027
https://hal.archives-ouvertes.fr/hal-00456027
DOI : 10.1029/2008GC002167

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We present a 2-D Contact Dynamics discrete element model for simulating initiation and motion of rock avalanches, integrating hillslope geometry, Mohr-Coulomb rock behavior, pore pressure before avalanche triggering, and avalanche trigger. Avalanche motion is modeled as a dense granular flow of dry frictional and cohesive particles. On the basis of granular physics and shear experiments, we review some of the theories for the unexpectedly long runout of rock avalanches. Different causes are evoked, according to the strength (strong or weak) of the slip surface relative to the bulk. "Mechanical fluidization'' and "acoustic fluidization'' theories state that agitation of rock particles reduces frictional strength, increasing runout. Conversely, granular mechanics suggests that, as "shear-strain'' rate increases, granular material becomes more agitated, more dissipative, and more resistant. Another theory states that dynamic fragmentation of clasts creates an isotropic pressure that drives longer runout. In contrast, granular mechanics suggests that fragmentation may induce fluidization and strengthening of the granular material, while particle size reduction (among others) induces weakening of the granular flow and enhances long runout. Runout is also enhanced for column-like rock masses collapsing from steep hillslopes. Long runout may also be linked to thermal weakening mechanisms at the slip surface (e.g., thermal pressurization, and shear melting), which may lower drastically the shear strength. The model is illustrated with a hypothetical example of a rain-triggered avalanche, mobilizing shallowly dipping layers. Several phases are identified, including slope failure, avalanche triggering resulting from slip weakening, and avalanche motion in which rocks are folded and sheared.
ISSN: 0148-0227

hal-00420883
https://hal.archives-ouvertes.fr/hal-00420883
DOI : 10.1029/2008JF001072

Éditeur(s) : HAL CCSD Elsevier
Résumé : We use a triangular representation of the plunges of P, B, and Taxes to compare the different ways tectonic regime is inferred from earthquake focal mechanisms in recent works. We argue that P, B, and Taxes provide a reasonable estimate of principal stress directions when faulting is close to Andersonian conditions, and that this can be estimated from the location on a triangular diagram. We analyze the geometrical relationship between the plunges of P, B, and Taxes on one hand, and the rake of slip and dip of nodal planes on the other hand. We show that the rake and dip level curves correspond to trajectories of the vertical direction along great and small circles with respect to the frame of the P, B. and Taxes. This shows that dip-slip faulting is compatible with vertical P or Taxes, but does not require it, and instead requires horizontal B axes. It also shows that strike-slip faulting does not require vertical B axes, but P and Taxes with equal plunges. This also reveals that focal mechanisms where P, B, and Taxes all have moderate plunge correspond to two very different types of nodal planes: a steeply dipping one with oblique slip and a moderately dipping one with strike-slip. Seismically active and moderately dipping strike-slip faults are to be found among these events.
ISSN: 0040-1951

hal-00486367
https://hal.archives-ouvertes.fr/hal-00486367
DOI : 10.1016/j.tecto.2009.03.006

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Zandjan province is situated in the NW of Iran, at the junction between the southern termination of the Tabriz right-lateral strike-slip fault and the western end of the Alborz active mountain range. Despite this key location, in terms of active tectonics, there is no destructive earthquake reported in available historical seismicity catalogues. Even if a few low magnitude instrumental earthquakes have been recorded indicating that this area is actively deforming, the Zandjan region can be considered as a seismic gap. Based on detailed field investigations, digital elevation models (DEMs), satellite image and aerial photo interpretations, we have identified a major active fault network affecting this regions. It is mainly constituted by several west and est verging thrust faults, trending NW-SE to N-S, that clearly cut Late Quaternary to Holocene deposits. Evidences in the morphology indicate also that they accommodate some right-lateral slip component. This fault network can be divided into four major fault zones affecting Zandjan city (present day population over 500,000) and part of the Zandjan-Mianeh basin more to the west. Based on fault geometrical characteristics (fault length, segmentation ... ) and kinematics, the Zandjan fault system is certainly capable to produce moderate to large earthquakes (Mw = 6.5-7.0) and serious damages in the Zandjan city and surrounding areas. The study of these faults is, then, of major interest for seismic hazard assessment in Zandjan province where total population exceed 1.5 million but also to better understand present day geodynamic of NW Iran.
ISSN: 0040-1951

hal-00617526
https://hal.archives-ouvertes.fr/hal-00617526
DOI : 10.1016/j.tecto.2011.04.012

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : International audience
The seismological study of recent seismic crises near Oleron Island confirms the coexistence of an extensional deformation and a transtensive regime in the Atlantic margin of France, which is different from the general western European stress field corresponding to a strike-slip regime. We argue that the switch of the principal stress axes σ1/σ2 in a NW-SE vertical plane is linked with the existence of crustal heterogeneities. Events of magnitude larger than 5 sometimes occur along the Atlantic margin of France, such as the 7 September 1972 (ML = 5.2) earthquake near Oleron island and the 30 September 2002 (ML = 5.7) Hennebont event in Brittany. To test the mechanism of local strain localization, we model the deformation of the hypocentral area of the Hennebont earthquake using a 3D thermo-mechanical finite element code. We conclude that the occurrence of moderate earthquakes located in limited parts of the Hercynian shear zones (as the often reactivated swarms near Oleron) could be due to local reactivation of pre-existing faults. These sporadic seismic ruptures are favoured by stress concentration due to rheological heterogeneities.
ISSN: 1631-0713

hal-00936220
https://hal.archives-ouvertes.fr/hal-00936220
DOI : 10.1016/j.crte.2013.07.004

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
During the last decade, the interaction of deep processes in the lithosphere and mantle with surface processes (erosion, climate, sea-level, subsidence, glacio-isostatic readjustment) has been the subject of heated discussion. The use of a multidisciplinary approach linking geology, geophysics, geodesy, modelling, and geotechnology has led to the awareness of coupled deep and surface processes. Deep earth dynamics (topography, erosion, tectonics) are strongly connected to natural hazards such as earthquakes, landslides, and tsunamis; sedimentary mass transfers have important consequences on isostatic movements and on georesources, geothermal energy repartitions. The ability to read and understand the link between deep Earth dynamics and surface processes has therefore important societal impacts. Ground-truthing at carefully-selected sites of investigation is imperative to better understand these connections.Due to its youth (<30 Ma) and its subsidence history, the almost land-locked Gulf of Lion–Sardinia continental margins system provides a unique record of sedimentary deposition from the Miocene to present. Due to its high subsidence rate, palaeoclimatic variations, tectonic events and vertical evolution are all recorded here at very high resolution. The late Miocene isolation and desiccation of the Mediterranean, the youngest and most catastrophic event, the Messinian Salinity Crisis (MSC), induced drastic changes in marine environments: widespread deposition of evaporite (gypsum, anhydrite and halite) in the central basin, and intense subaerial erosion along its periphery. These extraordinary mass transfers from land to sea induced strong isostatic re-adjustments that are archived in the sedimentary record and represent a window to the lithospheric rheology and the deep processes.The GOLD (Gulf of Lion Drilling) project, proposes to explore this unique sedimentary record as well as the nature of the deep crustal structure, providing valuable information about the mechanisms underlying vertical motions in basins and their margins.
ISSN: 0264-8172

insu-01197393
https://hal-insu.archives-ouvertes.fr/insu-01197393
https://hal-insu.archives-ouvertes.fr/insu-01197393/document
https://hal-insu.archives-ouvertes.fr/insu-01197393/file/Rabineau%20et%20al.-final-MPG2014_REVISED-FINAL-No-Marked_FINAL%2BFigures.pdf
DOI : 10.1016/j.marpetgeo.2015.03.018

Éditeur(s) : American Geophysical Union
Résumé : Magmatism associated with subducting plate edges or slab tears has been suggested in the southern Okinawa Trough. The cross back-arc volcanic trail, which consists of a cluster of about 70 seamounts, is located above a Ryukyu slab tear lying along the 123.3°E meridian. In November 2003, more than 3300 earthquakes recorded in this area by 15 ocean bottom seismometers and surrounding land stations during a period of 12 days were used to determine the three-dimensional Vp and Vs velocity structures and Vp/Vs ratios. A mantle inflow characterized by low Vp and Vs and high Vp/Vs passing through the slab tear is imaged. The fluid and/or melt component is rising obliquely from the slab tear in the directions of the cross back-arc volcanic trail, the northern slope of the southern Okinawa Trough and to north of Iriomote Island. The asthenospheric intake is also imaged by an inclined chip-like high Vp/Vs and low Vp and Vs body dipping northerly, which might be linked to the slab retreat. West of the slab tear, most of the earthquakes are located around low Vp and Vs and high Vp/Vs bodies, which suggests that the seismicity is related to magmatic and/or fluid activities. East of it, earthquakes are concentrated in an area characterized by high Vp and Vs velocities and low Vp/Vs, suggesting that the magma chamber is absent beneath the axial part of the trough and that normal faulting is the main factor controlling the seismicity.
Journal of Geophysical Research ( JGR ) - Solid earth (0148-0227) (American Geophysical Union), 2007-08 , Vol. 112 , N. B8 , P. NIL_13-NIL_32

Droits : 2007 AGU
http://archimer.ifremer.fr/doc/2007/publication-3032.pdf
DOI:10.1029/2006JB004703
http://archimer.ifremer.fr/doc/00000/3032/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Taiwan area, where the Philippine Sea Plate collides with Eurasia, is one of the most seismically active areas in the world and has been consequently struck repeatedly by destructive earthquakes. To better constrain the occurrence of large earthquakes, we have conducted two cruises in 2012 and 2013 from which five piston, gravity and box-cores were retrieved from selected sites in targeted areas that contain continuous and accurate turbidite deposition offshore eastern Taiwan. Forty-seven turbidite layers deposited between 675 BC and 2012 AD have been described in the cores with facies varying from silty clay to coarse sand. We modeled each turbidite layer using the sedimentation rate deduced from radiocarbon age measurements performed on planktonic foraminifers. Precise dating based on 210Pb–137Cs chronology provided ages for the XXth century turbidites. Coring sites' locations, biotic association within turbidites beds and seismic calibration over the instrumental period, suggest that earthquakes are the most likely triggering mechanisms of turbidity currents over the last 2700 years. Calibration of correlations between turbidites and instrumental earthquakes allowed us to determine the minimum magnitude of recorded events (Mw = 6.8) and the maximum distance between the epicenter and the slope failure. Turbidites' synchroneity between cores has been tested but results showed that this criterion cannot be used in our study area because of the high level of seismicity, i.e., a M > 6.8 earthquake recurrence interval much smaller than the uncertainty on radiocarbon ages. The excellent accuracy of dating allows correlating all the turbidites deposited since 1920 with instrumental earthquakes. For each core, we established a return time ranging between 112 and 147 years for the period pre-1900 and ~ 27 and 34 years for the period post-1900. The discrepancy between pre-1900 and post-1900 recurrence either suggests, that slope stability varies, with higher slope instability after 1900 possibly due to increased sediment delivery by rivers.
ISSN: 0040-1951

hal-01467627
https://hal.archives-ouvertes.fr/hal-01467627
DOI : 10.1016/j.tecto.2016.04.030

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We have discovered in a marine core, located 20 km east of the Coastal Range of Taiwan at the top of a 1200 m deep submarine high, sheltered from rivers discharges and gravitational flows, a 23 cm-thick anomalous sequence topped with broken bivalves and wood fragments. Based on radiocarbon dating, we distinguish five sub-events within ∼ 100 yrs, about 3000 years ago. The oldest four sub-events are interpreted as the record of local submarine landslides, likely triggered by clustered earthquakes that are common in this tectonically active area. The last event including shells and wood has a different origin. Despite the high level of climatic and tectonic recent activity, no comparable event has been observed at the same site since that time, making it unique during the last 3.75 ka. Hydrodynamical modeling stimulated with a set of submarine landslide-triggered tsunami sources and combined with the regional oceanic circulation dominated by the Kuroshio Current, allow us to better constrain the transport paths of the suspended material, the expected run-up at the coast, and ultimately the trigger and source that best fit our observations. The Kuroshio Current appears as a strong constraint that generally prevents cross-shore transport of suspended material even during a major tsunami. Since the largest aerial debris flow observed along the east coast of Taiwan during the last 4 ka was synchronous with the marine deposit, our preferred scenario starts with the occurrence of four distinct large earthquakes within less than a century, triggering both submarine and aerial landslides in the study area. Then, a giant typhoon reworked the nearshore material as well as the slided material stored upstream resulting in a debris flow. It deeply modified the surface current, allowing the wood debris and shells to fastly reach the core site.
ISSN: 0040-1951

hal-01467640
https://hal.archives-ouvertes.fr/hal-01467640
DOI : 10.1016/j.tecto.2015.11.001

Éditeur(s) : HAL CCSD Copernicus Publications on behalf of the European Geosciences Union
Résumé : International audience
During the GWADASEIS cruise (Lesser Antilles volcanic arc, February–March 2009) a very high resolution (VHR) seismic-reflection survey was performed in order to constrain Late Quaternary to Present faulting. The profiles we obtained evidence frequent " ponding " of reworked sediments in the deepest areas, similar to the deposition of Mediterranean " homogenites ". These bodies are acoustically transparent (few ms t.w.t. thick) and are often deposited on the hanging walls of dominantly normal faults, at the base of scarps. Their thickness appears sufficient to compensate (i.e. bury) co-seismic scarps between successive earthquakes, resulting in a flat and horizontal sea floor through time. In a selected area (offshore Montserrat and Nevis islands), piston coring (4 to 7 m long) was dedicated to a sedimento-logical analysis of the most recent of these particular layers. It corresponds to non-stratified homogenous calcareous silty sand (reworked calcareous plankton and minor volcanoclas-tics). This layer can be up to 2 m thick, and overlies fine-grained hemipelagites. The upper centimeters of the latter represent the normal RedOx water/sediment interface. 210 Pb and 137 Cs activities lack in the massive sands, while a normal profile of unsupported 210 Pb decrease is observed in the hemipelagite below, together with a 137 Cs peak corresponding to the Atmospheric Nuclear Experiments (1962). The RedOx level was thus capped by a recent instantaneous major sedimentary event considered as post-1970 AD; candidate seismic events to explain this sedimentary deposits are either the 16 March 1985 earthquake or the 8 October 1974 one (M w = 6.3 and M w = 7.4, respectively). This leads to consider that the syntectonic sedimentation in this area is not continuous but results from accumulation of thick homogen-ites deposited after the earthquakes (as observed in the following weeks after Haiti January 2010 event, McHugh et al., 2011). The existence of such deposits suggests that, in the area of study, vertical throw likely results from cu-mulated effects of separated earthquakes rather than from aseismic creep. Examination of VHR profiles shows that all major co-seismic offsets are recorded in the fault growth sequence and that co-seismic offsets can be precisely estimated. By using a sedimentation rate deduced from 210 Pb decrease curve (0.5 mm yr −1) and taking into account minor reworking events detected in cores, we show that the Redonda system may have been responsible for five > M 6 events during the last 34 000 yr. The approach presented in this work differs from fault activity analyses using displaced sets of isochronous surfaces and postulating co-seismic offsets. Combining VHR seismic imagery and coring we can decipher co-seismic vs. slow continuous displacement, and thus actually estimate the amplitude and the time distribution of major co-seismic offsets.
Natural Hazards and Earth System Science

insu-01585969
https://hal-insu.archives-ouvertes.fr/insu-01585969
https://hal-insu.archives-ouvertes.fr/insu-01585969/document
https://hal-insu.archives-ouvertes.fr/insu-01585969/file/nhess-12-1755-2012-beck.pdf
DOI : 10.5194/nhess-12-1755-2012

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Longmen Shan range is one of the major topographic and structural features of the easternmargin of the Tibetan Plateau. With an impressive topographic gradient and low convergence rates across the range this region has raised important questions concerning the dynamics of plateaumargin settings, such as the long-term mechanisms of topographic evolution. The investigation of the distribution in space and time of denudation can provide critical insight into such dynamics and shed light on still unresolved controversies. For that purpose, we present a new dataset that documents the intensity and distribution of denudation processes across this plateaumargin through field survey of fluvial incision markers, quantitative geomorphology and cosmogenic nuclide derived basin-wide erosion rates. Erosion is < 0.5 mm/year in the frontal region of the Longmen Shan and between 0.5 and 1 mm/year further west, with a gradual decrease when reaching the northern headwaters of the Min Jiang watershed, adjacent to the beginning of the Tibetan Plateau. The spatialdistribution of denudation inferred from the various methods we use suggests that most of the differential uplift in the Central Longmen Shan is accommodated by the Beichuan Fault and frontal structures located in the foothills. The denudation pattern seems also to reflect the large-scale propagation of erosion from the Sichuan Basin toward the Plateau. This suggests that the Longmen Shan range is submitted to the combined influences of slow thrusting activity on the frontal structures and progressive westward regressiveerosion as a probable response to a pulse of uplift of the Tibetan PlateauEasternmargin, that started 10 Ma ago.
ISSN: 0040-1951

hal-01564192
https://hal.archives-ouvertes.fr/hal-01564192
DOI : 10.1016/j.tecto.2009.10.026

Éditeur(s) : HAL CCSD Geological Society of America
Résumé : International audience
Fault pseudotachylytes form by frictional melting during seismic slip and therefore are widely interpreted as “earthquake fossils.” Rapid movement along a rupture surface typically forms a pseudotachylyte generation vein, the thickness of which increases with earthquake magnitude. The direction and sense of seismic slip cannot always be determined due to the generally complex geometry of pseudotachylyte veins. Here we show, for the first time, that the orientation of the magnetic fabric of fault pseudotachylytes indicates both direction and sense of seismic slip. The magnetic fabric, acquired in a manner similar to that of other magmas, arises in this case from the asymmetric preferred orientation of paramagnetic grains during viscous shear of the friction melt. This kinematic information, coupled with fault plane orientation and generation vein thickness, provides new and critical insight for the earthquake focal mechanism. The magnetic fabric of pseudotachylytes therefore not only constitutes a valuable kinematic criterion for these fault rocks, but also could expand our knowledge of prehistoric seismic events.
ISSN: 0091-7613

hal-01217133
https://hal.archives-ouvertes.fr/hal-01217133
DOI : 10.1130/G36587.1

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
We analyze focal mechanisms of shallow-intermediate earthquakes in a NW-SE transect along the western Betic Cordillera and Alboran Sea, and deep earthquakes located in the central Betics to constrain the state of stress at the Gibraltar Arc slow convergence area. Shallow earthquakes (< 40 km) are preferably clustered at the mountain front. A general NW-SE horizontal compression is compatible with the convergence, and NW plunging compression axes are in agreement with frontal thrust activity. Toward the Alboran Sea the earthquakes are progressively deeper, reaching intermediate depths (40-120 km) near the coast and supporting the present-day activity of subduction only in this area. The Iberian continental crust concentrates most of the intermediate seismicity and is forced to partially sink into the mantle, probably through the pull of the oceanic slab. This downdip pull together with the buoyancy of the Iberian continental crust produces the slab curvature, downdip extension in the external arc of the continental slab, and downdip compression in the inner arc. T axes highly dipping to the southeast at 90-120 km depth occur at the oceanic/continental transition. Deep earthquakes (> 620 km) show very similar focal mechanisms, fitting the general slab behavior of resistance to further descent at the 660 km discontinuity. Seismicity features evidence the present-day stress distribution in a context of transition from subduction to continental collision.
ISSN: 1525-2027

hal-00669889
https://hal.archives-ouvertes.fr/hal-00669889
DOI : 10.1029/2011GC003824

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
Temperature and fluid pressure conditions control rock deformation and mineralization on geological faults, and hence the distribution of earthquakes1. Typical intraplate continental crust has hydrostatic fluid pressure and a near-surface thermal gradient of 31 ± 15 degrees Celsius per kilometre2, 3. At temperatures above 300–450 degrees Celsius, usually found at depths greater than 10–15 kilometres, the intra-crystalline plasticity of quartz and feldspar relieves stress by aseismic creep and earthquakes are infrequent. Hydrothermal conditions control the stability of mineral phases and hence frictional–mechanical processes associated with earthquake rupture cycles, but there are few temperature and fluid pressure data from active plate-bounding faults. Here we report results from a borehole drilled into the upper part of the Alpine Fault, which is late in its cycle of stress accumulation and expected to rupture in a magnitude 8 earthquake in the coming decades4, 5. The borehole (depth 893 metres) revealed a pore fluid pressure gradient exceeding 9 ± 1 per cent above hydrostatic levels and an average geothermal gradient of 125 ± 55 degrees Celsius per kilometre within the hanging wall of the fault. These extreme hydrothermal conditions result from rapid fault movement, which transports rock and heat from depth, and topographically driven fluid movement that concentrates heat into valleys. Shear heating may occur within the fault but is not required to explain our observations. Our data and models show that highly anomalous fluid pressure and temperature gradients in the upper part of the seismogenic zone can be created by positive feedbacks between processes of fault slip, rock fracturing and alteration, and landscape development at plate-bounding faults.
ISSN: 0028-0836

hal-01685757
https://hal.archives-ouvertes.fr/hal-01685757
DOI : 10.1038/nature22355

Éditeur(s) : Université des Antilles Études caribéennes
Résumé : La question de l’attractivité est souvent évoquée par plusieurs auteurs pour expliquer les mobilités étudiantes, qu’elles soient internationales ou régionales. L’attractivité du pays d’accueil ou des universités accueillantes font ainsi partie des logiques explicatives avancées. Ce papier part du contexte de crise universitaire et académique généré par le séisme de 2010 à Haïti pour réfléchir sur les fluctuations de la notion d’attractivité dans le cadre de mobilités étudiantes quasiment forcées et actées depuis des pays africains. Et ceci, en examinant des programmes de mobilité proposés par le Bénin et le Sénégal aux étudiants haïtiens au moment où la plupart des pays du Nord optaient davantage pour une délocalisation des étudiants haïtiens ou un maintien sur place. Notre propos relativise fortement le critère d’attractivité comme déterminant majeur des mobilités étudiantes en contexte de crise de l’institution universitaire.
The issue of attractiveness is often mentioned by several authors to explain international or regional student’s mobilities. The attractiveness of the host country, or host universities are part of the explanatory logic’s scheme. This paper mobilizes the context of academic crisis generated by the 2010’s earthquake in Haiti to examine the meanings of the concept of attractiveness in the almost forced student mobility and originated from African countries. And this, by examining institutional and political springs of mobility programs offered by Benin and Senegal to Haitian students while most northern countries opted to relocate Haitian students or maintain them on site. Our analysis highly relativizes attractiveness as major determinant of student mobility in the context of academic crisis generated by natural disaster.
Bénin
Haïti
Sénégal

Droits : info:eu-repo/semantics/openAccess
urn:doi:10.4000/etudescaribeennes.7578
http://journals.openedition.org/etudescaribeennes/7578

Éditeur(s) : HAL CCSD
Résumé : The Astaneh fault with a length of more than 75 km is located in NW of Damghan. Morphotectonic investigation along the Astaneh fault and left - lateral displacement in quaternary deposits shows that, Astaneh is an active fault. It is necessary to recognize paleoseismicity of Astaneh fault because, this fault is located in seismic zone of Komes historical earthquake with Ms=7.9 (Ambraseys & Melville, 1982). Many people (more than 45000) were killed in Damghan city in Komes historical earthquake. In this paper, 4-5 paleo events along the Astaneh fault are presented through paleoseismological investigation.
Geosciences Scientific Quarterly Journal

hal-00854396
https://hal.archives-ouvertes.fr/hal-00854396

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The reactivation of faults with near-optimal orientations is commonly considered to control the state of stress in the crust. Near the surface, where a principal stress direction is vertical, the attitude of such faults is explained by Anderson's theory. This raises the questions of how prevalent this type of faulting actually is in current seismicity, down to what depth it frequently occurs, and what range of friction angles explains it best. The Global Centroid Moment Tensor catalog is analyzed to address these questions. Dip-slip and strike-slip mechanisms are dominant, and oblique slips are relatively rare for well-constrained events with depths shallower than 30 km. Preferred Andersonian faulting is the simplest, but not the unique, explanation for this dominance. Isolating reverse, strike- slip, and normal events reveals an asymmetry in the distribution of nodal plane dips and plunges of the P, B, and T axes between reverse and normal faulting. Assuming that the most frequent events correspond to reactivation near optimal orientations yields 40-60 degrees and 0-20 degrees friction angles for reverse and normal faults, respectively. This indicates that reverse and normal faulting mechanics are not symmetrical with respect to stress configuration as predicted by Anderson's theory.
ISSN: 8755-1209

hal-00412159
https://hal.archives-ouvertes.fr/hal-00412159
DOI : 10.1029/2007RG000240

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Properly assessing the extent and magnitude of fault ruptures associated with large earthquakes is critical for understanding fault behavior and associated hazard. Submarine faults can trigger tsunamis, whose characteristics are defined by the geometry of seafloor displacement, studied primarily through indirect observations (e.g., seismic event parameters, seismic profiles, shipboard bathymetry, coring) rather than direct ones. Using deep-sea vehicles, we identify for the first time a marker of coseismic slip on a submarine fault plane along the Roseau Fault (Lesser Antilles), and measure its vertical displacement of ∼0.9 m in situ. We also map recent fissuring and faulting of sediments on the hangingwall, along ∼3 km of rupture in close proximity to the fault's base, and document the reactivation of erosion and sedimentation within and downslope of the scarp. These deformation structures were caused by the 2004 M w 6.3 Les Saintes earthquake, which triggered a subsequent tsunami. Their characterization informs estimates of earthquake recurrence on this fault and provides new constraints on the geometry of fault rupture, which is both shorter and displays locally larger coseismic displacements than available model predictions that lack field constraints. This methodology of detailed field observations coupled with near-bottom geophysical surveying can be readily applied to numerous submarine fault systems, and should prove useful in evaluating seismic and tsunamigenic hazard in all geodynamic contexts.
ISSN: 0012-821X

insu-01557932
https://hal-insu.archives-ouvertes.fr/insu-01557932
https://hal-insu.archives-ouvertes.fr/insu-01557932/document
https://hal-insu.archives-ouvertes.fr/insu-01557932/file/EPSL-2006-escartin.pdf
DOI : 10.1016/j.epsl.2016.06.024

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We use velocities from 65 continuous stations and 31 survey-mode GPS sites as well as kinematic modeling to investigate present day deformation along the Africa-Iberia plate boundary zone in the western Mediterranean region. The GPS velocity field shows southwestward motion of the central part of the Rif Mountains in northern Morocco with respect to Africa varying between 3.5 and 4.0 mm/yr, consistent with prior published results. Stations in the southwestern part of the Betic Mountains of southern Spain move west-southwest with respect to Eurasia (similar to 2-3 mm/yr). The western component of Betics motion is consistent with partial transfer of Nubia-Eurasia plate motion into the southern Betics. The southward component of Betics motion with respect to Iberia is kinematically consistent with south to southwest motion of the Rif Mountains with respect to Africa. We use block modeling, constrained by mapped surface faults and seismicity to estimate the geometry and rates of strain accumulation on plate boundary structures. Our preferred plate boundary geometry includes one block between Iberia and Africa including the SW Betics, Alboran Sea, and central Rif. This geometry provides a good fit to the observed motions, suggesting a wide transpressive boundary in the westernmost Mediterranean, with deformation mainly accommodated by the Gloria-Azores fault system to the West and the Rif-Tell lineament to the East. Block boundaries encompass aspects of earlier interpretations suggesting three main deformation styles: (i) extension along the NE-SW trending Trans-Alboran shear zone, (ii) dextral strike-slip in the Betics corresponding to a well defined E-W seismic lineament, and (iii) right lateral strike-slip motion extending West to the Azores and right-lateral motion with compression extending East along the Algerian Tell. We interpret differential motion in the Rif-Alboran-Betic system to be driven both by surface processes related the Africa-Eurasia oblique convergence and sub-crustal dynamic processes associated with the long history of subduction of the Neotethys ocean lithosphere. The dextral slip identified in the Betic Mountains in Southern Spain may be related to the offshore fault that produced the Great 1755 Lisbon Earthquake, and as such may represent a significant seismic hazard for the West Mediterranean region.
ISSN: 0012-821X

hal-00618337
https://hal.archives-ouvertes.fr/hal-00618337
DOI : 10.1016/j.epsl.2011.05.048

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The 12 May 2008 the Sichuan earthquake was one of the worst natural disasters in China. Here, we present a detailed picture of the epicentral area inferred geophysical data. Based on the analysis of teleseismic data acquired by a dense seismic network, we highlight an abrupt 20 km Moho offset between the Sichuan Basin and the Tibetan plateau and a horizontal discontinuity at similar to 15 km depth, which may connect with the ruptured zone of the 2008 event. We obtain low mean crustal velocity ratios, which suggest the absence of a thick and extensive zone of partial melt within the crust beneath the eastern part of the Songpan-Garze Terrane. All our data support the idea that the Longmen Shan range mark a zone of active strain localization due to the rigid Yangtze craton resisting eastward displacement of the Tibetan Plateau.
ISSN: 0040-1951

hal-00534471
https://hal.archives-ouvertes.fr/hal-00534471
DOI : 10.1016/j.tecto.2009.11.010