Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Mosha and North Tehran faults correspond to the nearest seismic sources for the northern part of the Tehran megacity. The present-day structural relationships and the kinematics of these two faults, especially at their junction in Lavasanat region, is still a matter of debate. In this paper, we present the results of a morphotectonic analysis (aerial photos and field investigations) within the central part of the Mosha and eastern part of the North Tehran faults between the Mosha valley and Tehran City. Our investigations show that, generally, the traces of activity do not follow the older traces corresponding to previous long-term dip-slip thrusting movements. The recent faulting mainly occurs on new traces trending E-W to ENE-WSW affecting Quaternary features (streams, ridges, risers, and young glacial markers) and cutting straight through the topography. Often defining en-echelon patterns (right- and left-stepping), these new traces correspond to steep faults with either north- or south-dipping directions, along which clear evidences for left-lateral strike-slip motion are found. At their junction zone, the two sinistral faults display a left-stepping en-echelon pattern defining a positive flower structure system clearly visible near Ira village. Further west, the left-lateral strike-slip motion is transferred along the ENE-WSW trending Niavaran fault and other faults. The cumulative offsets associated with this left-lateral deformation is small compared with the topography associated with the previous Late Tertiary thrusting motion, showing that it corresponds to a recent change of kinematics.
ISSN: 0040-1951

hal-00617778
https://hal.archives-ouvertes.fr/hal-00617778
DOI : 10.1016/j.tecto.2010.09.013

Éditeur(s) : HAL CCSD Universidad Complutense de Madrid
Résumé : Based on new seismological and recent faulting data, we analyze five main sectors in the western part of the Betic Cordillera from an active tectonic perspective: i. The northwestern frontal sector of the cordillera, including the Morón de la Frontera area, with shallow (< 15 km depth) seismogenic active NE-SW reverse and strike-slip faults that do not reach the surface. ii. The Teba area, in the External Zones, which is deformed by sparse N-S to NW-SE normal faults with associated wedges of Quaternary sediments and active strike-slip faults at intermediate crustal levels. iii. The Ronda Basin, representing the major Late Miocene intramontane basin of the western Betic Cordillera, is mainly deformed by NNE-SSW and WNW-ESE folds and locally by NW-SE normal faults. iv. The internal part of the orogen, which is characterized by shallow (<40 km) and intermediate (40 to 120 km depth) seismicity beneath Málaga and the Alborán Sea, ENE-WSW folding, relief uplift, river incision and scarce active faults with surface expression. v. The Spanish Atlantic coast, which coincides with the western end of the Betic orogen, where Pliocene to Quaternary shallowmarine sedimentary rocks are deformed by meso-scale NW-SE oriented normal faults and few ENE-WSW reverse faults. These data support the recent tectonic activity of the western Betic Cordillera determined by the NW-SE Eurasian-African convergence with variable features from the mountain front, characterized by shallow deformations, up to the Internal Zones that mainly undergo uplift and intermediate seismicity.
ISSN: 1698-6180

hal-00750359
https://hal.archives-ouvertes.fr/hal-00750359
DOI : 10.5209/rev_JIGE.2012.v38.n1.39211

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This study analyzes the active tectonics within the northwestern and southeastern extensions of the Pambak-Sevan-Syunik fault (PSSF), a major right-lateral strike-slip fault cutting through Armenia. Quantifying the deformations in terms of geometry, kinematics, slip rates and earthquake activity, using cosmogenic 3He, OSL/IRSL and radiocarbon dating techniques, reveal different behaviors between the two regions. Within the northwestern extension, in the region of Amasia, the PSSF bends to the west and splits into two main WNW–ESE trending reverse faults defining a compressional pop-up structure. We estimate an uplift rate and a shortening rate of 0.5 ± 0.1 mm/y and 1.4 ± 0.6 mm/y, respectively. This suggests that most of the ∼2 mm/y right lateral movement of the PSSF seems to be absorbed within the Amasia pop-structure. Within the southeastern extension, the PSSF shows signs of dying out within the Tsghuk Volcano region at the southernmost tip of the Syunik graben. There, the tectonic activity is characterized by a very slow NS trending normal faulting associated with a slight right-lateral movement. Slip rates analyses (i.e. vertical slip rate, EW stretching rate at 90° to the fault, and right-lateral slip rate of ∼0.2 mm/y, ∼0.1 mm/y and ∼0.05 mm/y, respectively) lead to the conclusion that the right lateral movement observed further north along the PSSF is mainly transferred within other active faults further west within the Karabagh (Hagari fault or other structures further northwestwards). Comparing our slip rates with those estimated from GPS data suggests that most of the deformation is localized and seismic, at least within the Tsghuk region. The geometrical and kinematic pattern observed within the two terminations of the PSSF suggests that the fault and its surrounding crustal blocks are presently rotating anticlockwise, as also observed within the GPS velocity field. This is consistent with the recent kinematic models proposed for the Caucasus-Kura-South Caspian region and brings a new insight into the present geodynamics of Armenia.
ISSN: 1040-6182

hal-01307342
https://hal.archives-ouvertes.fr/hal-01307342
DOI : 10.1016/j.quaint.2015.05.021

Éditeur(s) : HAL CCSD
Résumé : This thesis aims to analyze the active tectonics and the seismic hazard for three main cities of NW Iran (Tehran, Tabriz and Zandjan) using morphotectonics and paleoseismology. Within the Tehran capital, we focused our analysis on the Mosha-North Tehran (M-NT) active fault system. Our investigations show that this fault system is mainly dominated by left-lateral faulting. Along the eastern part of the M-NT fault system, we found evidences of at least seven strong (M>7) paleoearthquakes during the past 10 ka (recurrence interval : 1100-1400 yrs). Our study along the central portion of the fault system (in Abali region) suggests that it corresponds probably to the source of the 1830 AD historical earthquake (M=7.1, Io= IX). Within Tabriz region, we studied the SE segment of the North Tabriz fault. We found evidences of at least three strong events, which occurred during the past 33.5 ka. The North Tabriz dextral fault corresponds to the central portion of a fault system (TFS), and contains two fault segments (NW and SE). Our paleoseismological analysis shows a variation of the slip rate, which decreases from NW to SE along the strike-slip fault. The western (Mishu) and eastern (Bozghush) terminations of the fault system correspond to oblique-compression zones. TFS belongs to the eastern portion of a regional fault system (GSKT), linking the active extension within the central part of the collision and the active compression to the East. Finally, we focus on the Zandjan area, where no important historical seismicitiy is recorded. There, based on morphotectonics analysis we discovered a large active fault network, whose southeastern part affects the Zandjan city. To conclude this work, we replace our observations within the general geodynamic framework of the Arabia- Eurasia collision. One of the striking pictures is the occurrence of opposite kinematics along the M-NT (and other range parallel faults within the south Central Alborz) and the North Tabriz fault systems that have the same trend. This shows the rapid variation of the regional stress field in the Northern Iran.
L'objectif de ce mémoire de thèse est l'étude de la tectonique récente et l'évaluation de l'aléa sismique pour trois villes importante, Téhéran, Tabriz et Zandjan, situées dans le nord-ouest de l'Iran. Dans la capitale de l'Iran, Téhéran, nous nous sommes concentrés sur le système de faille active de Mosha-Nord Téhéran. Nos travaux démontrent que ce système est essentiellement décrochant sénestre. Nos analyses paléosismologiques sur la portion est de ce système (dans la vallée de Tar) montrent au minimum les évidences de sept grands événements sismiques (M>7) pendant les derniers 10000 ans (l'intervalle de récurrence est de 1100 à 1400 ans). Les études que nous avons mené dans la partie centrale de ce système (région d'Abali) révèlent qu'il pourrait être la source du dernier événement sismique ayant affecté la ville de Téhéran en 1830 AD. Dans la région de Tabriz, nous nous sommes intéressés au segment SE de la faille décrochante dextre de Nord Tabriz où nous avons trouvé les évidences de trois grands séismes pendant les derniers 33500 ans. Nos études montrent que la faille Nord Tabriz qui est la portion centrale d'un système de faille (TFS) est constituée par deux segments NW et SE dextres. Notre étude paléosismologique suggère une variation de la vitesse qui diminue du NW vers SE le long de ces segments. Les extrémités ouest (Mishu) et est (Bozghush) de ce système correspondent à des zones compressives qui absorbent les déplacements horizontaux sur les segments NW et SE. D'un point de vue général la TFS est une partie d'un système de failles régionales (GSKT) qui relie une zone d'extension active dans la partie centrale de la collision Arabie-Eurasie et une zone de compression active à l'Est. Enfin, à Zandjan qui est une ville située dans une région de lacune sismique, nous avons découvert un important réseau de failles actives. Le tracé sud-est de ce réseau de failles passe par la ville de Zandjan. En conclusion, les localisations et les cinématiques des systèmes de faille étudiés sont discutées dans le cadre géodynamique général de la collision Arabie-Eurasie. On remarquera que la faille majeure de Nord Tabriz qui correspond essentiellement à un décrochement dextre a la même direction NW-SE que les décrochements sénestres présents dans la chaîne de l'Alborz (les failles de : Mosha, Talaghan et Manjil). Cette observation nécessite une variation de la direction de compression entre ces deux régions.
https://tel.archives-ouvertes.fr/tel-00539739

tel-00539739
https://tel.archives-ouvertes.fr/tel-00539739
https://tel.archives-ouvertes.fr/tel-00539739/document
https://tel.archives-ouvertes.fr/tel-00539739/file/thesesoleymani.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
During compressive events, deformation in sedimentary basins is mainly accommodated by thrust faulting and related fold growth. Thrust faults are generally rooted in the basement and may act as conduits or barriers for crustal fluid flow. Most of recent studies suggest that fluid flow through such discontinuities is not apparent and depends on the structural levels of the thrust within the fold-and-thrust belt. In order to constrain the paleofluid flow through the Jaca thrust-sheet-top basin (Paleogene southwest-Pyrenean fold-and-thrust belt) this study compares on different thrust faults located at different structural levels. The microstructures in the different fault zones studied are similar and consist of pervasive cleavage, calcite shear veins (SV1), extension veins (EV1) and late dilatation veins (EV3). In order to constrain the nature and the source of fluids involved in fluid-rock interactions within fault zones, a geochemical approach, based on oxygen and carbon stable isotope and trace element compositions of calcite from different vein generations and host rocks was adopted. The results suggest a high complexity in the paleohydrological behaviors of thrust faults providing evidence for a fluid-flow compartmentalization within the basin. Previous studies in the southern part of the Axial Zone (North of the Jaca basin) indicates a circulation of deep metamorphic water, probably derived from the Paleozoic basement, along fault zones related to the major basement Gavarnie thrust. In contrast, in northern part of the Jaca basin, the Monte Perdido thrust fault is affected by a closed hydrological fluid system involving formation water during its activity. The Jaca and Cotiella thrust faults, in turn, both located more to the south in the basin, are characterized by a composite fluid flow system. Indeed, stable isotope and trace element compositions of the first generations of calcite veins suggest a relatively closed paleohydrological system, whereas the late calcite vein generations, which are probably associated with the late tectonic activity of the basin, support a contribution of both meteoric and marine waters. Based on these results, a schematic fluid-flow model is presented. This model allows visualization of three main fluid flow compartments along a N-S transect.
ISSN: 0264-8172

hal-00963606
https://hal.archives-ouvertes.fr/hal-00963606
DOI : 10.1016/j.marpetgeo.2013.09.005

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
New high-resolution marine data acquired aboard R/V Le Suroît was used to map active normal faults offshore Montserrat in greater detail. The main faults of the Montserrat-Havers fault zone have cumulative scarps up to 200 m high, and offset sedimentary layers by hundreds of meters. They are arranged in a right-stepping, en echelon, trans-tensional array, which confirms that they accommodate the left-lateral component of motion resulting from slip partitioning of oblique convergence along the volcanic arc. They cut across Montserrat's recent volcanic complex. Faulting and fissuring exerted control on the position of andesitic domes, which are aligned along the N110°E average fault trend. The ≈10 km-long fault segments that cross the island could produce damaging, M ≈ 6 events comparable to the shallow, 16 March 1985, Mw∼6.3 earthquake that ruptured a submarine, N140°E striking, left-lateral fault near Redonda.
ISSN: 0094-8276

insu-01586768
https://hal-insu.archives-ouvertes.fr/insu-01586768
https://hal-insu.archives-ouvertes.fr/insu-01586768/document
https://hal-insu.archives-ouvertes.fr/insu-01586768/file/Feuillet_et_al-2010-Geophysical_Research_Letters.pdf
DOI : 10.1029/2010GL042556

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
P>The Strait of Hormuz area is a transition zone between the continental collision of the Zagros (west) and the subduction of an oceanic part of the Arabian Plate beneath the Makran wedge (east). Geology and recent GPS measurements indicate that about 15 mm yr-1 of relative motion in N10 degrees E direction is accommodated by two major fault systems: (1) the NNW-trending Minab-Zendan-Palami (MZP) fault system that connects the Main Zagros Thrust (MZT) to the inner Makran thrust system and the Frontal subduction thrust and (2) the N-trending Sabzevaran-Kahnuj-Jiroft (SKJ) fault system that bounds the Jazmurian depression to the west. We use dense GPS measurements along four transects across these fault systems in order to determine the strains spatial distribution. The northern GPS transect confirms the total fault slip rates for both fault systems estimated by the tectonic analyses (about 10 and 7.3 mm yr-1 in N10 degrees direction across the MZP and SKJ fault systems, respectively). For both fault systems, the elastic deformation spreads over shear zones that are several tens of kilometres wide. However, transects located close to latitude 27 degrees N reveal a much narrower shear zone (similar to 10 km) for the MZP fault system. Moreover, we confirm that most of the present-day strain is transferred towards the frontal subduction thrust rather than towards the inner Makran thrusts. In order to complement this new GPS velocity field with spatially dense measurements, we processed a set of ERS radar images by the radar interferometry (InSAR) technique. We used both a 'stacking' and a 'persistant-scatterers' approach to differentiate the ground deformation signal which spatial gradient is expected to be very low, from the atmospheric signal. Results from these interferograms appear to be relatively in agreement with the GPS-determined strain distribution. Nevertheless, they confirm the absence of any superficial creep behaviour since no sharp discontinuity on interferometric phase can be noted on any interferogram. Finally, we use a purely kinematic 'block model' inversion process to calculate slip rates and locking depths for each fault system from our GPS measurements. These models suggest that the relative quiescence over the last 200 yr has certainly produced a slip deficit as high as 2 m. So, we may wonder if the MZP fault system is not late in the interseismic phase of its earthquake cycle.
ISSN: 0956-540X

hal-00429386
https://hal.archives-ouvertes.fr/hal-00429386
DOI : 10.1111/j.1365-246X.2009.04321.x

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
In places where sedimentation and erosion compete at fast rates, part of the record of past earthquakes on faults may be buried, hence hidden, in the first few metres below the surface. We developed a novel form of palaeoseismology, of geophysical type, based on the use of a dense pseudo-3-D Ground Penetrating Radar (GPR) survey to investigate such possible buried earthquake traces, on a long, fast-slipping strike-slip fault (Hope fault, New Zealand), at a site (Terako) where marked alluvial conditions prevail. We first used LiDAR data to analyse the ground surface morphology of the 2 km2 site at the greatest resolution. Nineteen morphological markers were observed, mainly alluvial terrace risers and small stream channels that are all dextrally offset by the fault by amounts ranging between 3 and 200 m. The measurements document about 10 past earthquake slip events with a mean coseismic slip of 3.3 +/- 1 m, with the most recent earthquake event having a slip of 3 +/- 0.5 m. We then investigated a detailed area of the site (400 x 600 m2) with pseudo-3-D GPR. We measured 56, similar to 400 m long, 510 m spaced GPR profiles (250 MHz), parallel to the fault and evenly distributed on either side. The analysis revealed the existence of a palaeosurface buried at about 3 m depth, corresponding to the top of alluvial terraces of different ages. That buried surface is incised by a dense network of stream channels that are all dextrally offset by the fault. We measured 48 lateral offsets in the buried channel network, more than twice than at the surface. These offsets range between 6 and 108 m, as observed at the surface, yet provide a more continuous record of the fault slip. The similarity of the successive slip increments suggests a slip per event averaging 4.4 +/- 1 m, fairly similar to that estimated from surface data. From the total surface and buried 67 offset collection, we infer that a minimum of 30 large earthquakes have broken the Hope fault at the Terako site in the last about 67 kyr, with an average coseismic slip of 3.2 +/- 1 m, a minimum average recurrence time of about 200 yr, and a magnitude of at least Mw 7.07.4. Our study therefore confirms that part of the record of past earthquakes may indeed reside in the first few metres below the surface, where it may be explored with geophysical, GPR-based palaeoseismology. Developing such a new palaeoseismological tool should provide rich information that may complement surface observations and help to document the past earthquakes on faults.
ISSN: 0956-540X

hal-00704560
https://hal.archives-ouvertes.fr/hal-00704560
DOI : 10.1111/j.1365-246X.2012.05366.x

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The North Tehran Fault (NTF) is located at the southernmost piedmont of Central Alborz and crosses the northern suburbs of the Tehran metropolis and adjacent cities, where ∼15 million people live. Extending over a length of about 110 km, the NTF stands out as a major active fault and represents an important seismic hazard for the Iranian capital after historical seismicity. In order to characterize the activity of the NTF in terms of kinematics, magnitude and recurrence intervals of earthquakes, we carried out a first paleoseismological study of the fault within its central part between Tehran and Karaj cities. We opened a trench across a 3 m-high fault scarp affecting Quaternary deposits. Our study shows that the scarp is the result of repeated events along a main N115°E trending shallow dipping thrust fault, associated with secondary ruptures. From the trench analysis and Infrared Stimulated Luminescence (IRSL) dating of fault-related sediments, we interpreted between 6 and 7 surface-rupturing events that occurred during the past 30 kyrs. Their magnitudes (estimated from the displacements along the faults) are comprised between 6.1 and 7.2. The two last events - the largest - occurred during the past 7.9 ± 1.2 ka, which yields a Holocene slip rate of ∼0.3 mm/yr. The 7 earthquakes scenario suggests a regular periodicity with a mean recurrence interval of ∼3.8 kyrs. However, the two most recent events could correspond to the two largest historical earthquakes recorded in the area (in 312-280 B.C. and 1177 A.D.), and therefore suggest that the NTF activity is not regular.
ISSN: 0148-0227

hal-00757568
https://hal.archives-ouvertes.fr/hal-00757568
https://hal.archives-ouvertes.fr/hal-00757568v2/document
https://hal.archives-ouvertes.fr/hal-00757568/file/ritz2012.pdf
DOI : 10.1029/2012JB009147

Éditeur(s) : HAL CCSD
Résumé : This work addresses a study of geodynamics in Armenia, a country located in the central part of the zone of continental collision between the Arabian and Eurasian lithosphere plates. The work includes two main parts: study of recent deformations of the lithosphere by means of GPS and detailed paleoseismological and morphometric investigations in the zone of the Artanish-Tskhouk segment of the PSSF. We analyze and compare rates of deformation determined by the GPS data and the rates estimated by the paleoseismological and morphometric studies. The Armenian-French network of GPS observations was installed in Armenia in 1998. Three observation sessions were conducted in 1998, 2000 and 2003. Based on the evidence obtained, a detailed study of the velocity field was conducted to analyze lithosphere deformation in Central and Northern Armenia. Slip rates were estimated for the principal active faults in Armenia. Several field works, including paleoseismological, archaeo-seismological, archaeological, geodetic and morphological studies, had been implemented in the zone of the Artanish-Tskhouk segment of the PSSF in 2003-2005. The fault was mapped in detail; rates of main horizontal and vertical slip along the fault were estimated and re-estimated. Four (4) paleo- and archeo-earthquakes were studied and dated. Eventually, the obtained data allowed us to re-estimate slip rates, maximum possible magnitudes and recurrence intervals of strong earthquakes on the Artanish-Tskhouk segment of the PSSF. A technique enabling estimation of horizontal and vertical displacements along strike-slip faults during paleo-earthquakes by the evidence obtained from paleo-seismological trenching was developed.
Les travaux présentés dans ce mémoire sont consacrés à l'étude de la géodynamique du territoire de l'Arménie qui est situé dans la partie centrale de la zone de collision continentale entre les plaques Arabique et Eurasienne. Le mémoire comprend deux parties principales: 1/ l'étude des déformations actuelles par la géodésie GPS; 2/ l'étude paléosismologique et morphométrique détaillée de la zone du segment d'Artanish-Tskhuk de la faille de Pambak-Sevan-Syunik (PSSF). On présente l'analyse et la comparaison des vitesses de déformations estimées par les données de GPS et par les données paléosismologiques et morphométriques. Le réseau d'observations GPS Arméno - Français a été installé en Arménie en septembre 1998. Trois campagnes de mesure du réseau ont été réalisées en 1998, 2000 et 2003. L'analyse détaillée du champ de vitesse à partir des données GPS a permis d'étudier et de quantifier les déformations actuelles de l'Arménie centrale et septentrionale. On a pu estimer les vitesses des déplacements des failles actives principales du territoire de l'Arménie. Un ensemble de travaux sur le terrain comprenant des recherches paléosismologiques, archéosismologiques, archéologiques, géodésiques, et morphologiques a été réalisé entre 2003 et 2005 dans la zone du segment d'Artanish-Tskhuk de la faille de PSSF. La cartographie détaillée de la faille a été réalisée et l'on a estimé et/ou re-estimés les déplacements horizontaux et verticaux le long de la faille. Quatre paléo- et archéoséismes ont été étudiés et datés. À partir des données obtenues, pour le segment d'Artanish-Tskhuk de la faille de PSSF, on a réévalué les vitesses de déplacements, la magnitude maximale possible, et l'intervalle récurrence des séismes forts. Une méthode d'évaluation des déplacements horizontaux et verticaux a été proposée à partir des logs de tranchées sur les failles de décrochements associées à des paléoséismes.
https://tel.archives-ouvertes.fr/tel-00551535

Droits : info:eu-repo/semantics/OpenAccess
tel-00551535
https://tel.archives-ouvertes.fr/tel-00551535
https://tel.archives-ouvertes.fr/tel-00551535/document
https://tel.archives-ouvertes.fr/tel-00551535/file/thesedavtyan2.pdf

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
The basis of this study is a new bathymetric map of the northeast Atlantic compiled from previously published maps made from conventional echosounder data, plus all Sea Beam data acquired on board the R/V JEAN CHARCOT since 1977. As most of the Sea Beam data have been obtained on the continental margin from Porcupine Seabight to the south of the Iberian Peninsula, a precise picture of the continental slope is given. A statistical analysis of the canyons, based on 750 measurements, reveals that many of the canyons present sharp changes in their direction, indicating a structural control mainly linked to the late Hercynian trends, especially around the Iberian Peninsula. Nevertheless, the paths of canyons may merely reflect recent gravity processes, as in the Porcupine Seabight. Canyons locally follow the directions of listric and associated transecting faults (Permian to Triassic and upper Jurassic to lower Cretaceous), as on the Celtic
ISSN: 0278-7407

hal-01261558
https://hal.archives-ouvertes.fr/hal-01261558
https://hal.archives-ouvertes.fr/hal-01261558/document
https://hal.archives-ouvertes.fr/hal-01261558/file/Lallemand1986-Tectonics.pdf
DOI : 10.1029/TC005i007p01125

Éditeur(s) : HAL CCSD The Geochemical Society of Japan
Résumé : International audience
The Western Cordillera of Ecuador consists of Cretaceous crustal fragments of oceanic plateaux and superimposed insular arcs, which were accreted to the northwestern South American margin during the Late Cretaceous and Paleocene. Slices of high-grade metabasites, ultramafic rocks, gabbros and basalts, unmetamorphosed radiolarian cherts and scarce garnet-bearing metasediments were randomly exhumed along Miocene to Recent transcurrent faults crosscutting the Western Cordillera. The basalts show geochemical characteristics of oceanic plateau basalts (flat REE patterns, La/Nb = 0.85). The gabbros differ from the basalts in having lower REE levels, positive Eu anomalies, and negative Nb and Ta anomalies; they are interpreted as resulting from arc magmatism. The amphibolites and banded amphibolites have major and trace element chemistry similar to that of oceanic plateau basalts (flat REE patterns, La/Nb = 0.86) or to cumulate gabbros. The granulite shares with oceanic plateaus similar trace element chemistry (flat REE patterns, La/Nb < 1) and εNdi values (+7.6). Continent-derived metasediments are depleted in heavy REE (La/Y = 4.8) and have a negative Eu anomaly. Foliated lherzolites, melagabbronorites and pyroxenites consist of serpentinized olivine + cpx + opx ± Ca-plagioclase. Lherzolites, melagabbronorites and pyroxenites are LREE depleted with positive Eu anomalies, while the harzburgite displays a U-shaped REE pattern. The trace element abundances of the ultramafic rocks are very low (0.1 to 1 times the chondritic and primitive mantle values). The ultramafic rocks represent fragments of depleted mantle, deformed cpx-rich cumulate, and continental lithospheric mantle or mantle contaminated by subduction-fluid. Except the scarce quartz-rich metasediments, all these rocks likely represent remnants of accreted oceanic crustal fragments and associated depleted mantle. Since these samples were randomly sampled at depth by the fault, we propose that the Western Cordillera and its crustal root are mainly of oceanic nature.
ISSN: 0016-7002

insu-00679228
https://hal-insu.archives-ouvertes.fr/insu-00679228

Éditeur(s) : HAL CCSD
Résumé : Guadeloupe Island (West French Indies) is one of the twenty islands that compose the Lesser Antilles Arc, which results from the subduction of the Atlantic Ocean plate beneath the Caribbean one. The island lies in a complex volcano-tectonic system and the need to understand its geological context has led to numerous on- and offshore geophysical investigations. This work presents the compilation and processing of available, on-land, airborne and marine, gravity and magnetic data acquired during the last 40 years on Guadeloupe Islands and at the scale of the Lesser Antilles Arc. The overall dataset provides new Bouguer and reduced to the pole magnetic anomaly maps at the highest achievable resolution. Regionally, the main central negative gravity trend of the arc allows defining two subsident areas. The first one is parallel to the arc direction (~N160°E) to the north, whereas the second unexpected southern one is oriented parallel to oceanic ridges (N130°E). Along the Outer Arc, the long wavelength positive anomaly is interpreted, at least along the Karukera Spur, as an up-rise of the volcanic basement in agreement with the seismic studies. To the NE of Guadeloupe, the detailed analysis of the geophysical anomalies outlines a series of structural discontinuities consistent with the main bathymetric morphologies, and in continuity of the main fault systems already reported in this area. Based on geophysical evidences, this large scale deformation and faulting of the Outer Arc presumably primarily affects the Atlantic subducting plate and secondarily deforms the upper Caribbean plate and the accretion prism. At the scale of Guadeloupe Island, joined gravity and magnetic modeling has been initiated based on existing interpretation of old seismic refraction profiles, with a general structure in three main layers. According to our geophysical anomalies, additional local structures are also modeled in agreement with geological observations: i) the gravity and magnetic signals confirm an up-rise of the volcanic basement below the limestone platforms outcropping on Grande-Terre Island ; ii) the ancient volcanic complexes of Basse-Terre Island are modeled with high density and reverse magnetized formations; iii) the recent volcanic centre is associated with formations consistent with the low measured density and the underlying hydrothermal system. The EW models coherently image a NNW-SSE depression structure in half-graben beneath Basse-Terre Island, its western scarp following the arc direction in agreement with bathymetric and seismic studies to the north of the island. The so-defined depressed area, and particularly its opening in half-graben toward the SW, is interpreted as the present-day front of deformation of the upper plate associated with the recent volcanic activity on and around Guadeloupe. Based on this regional deformation model, perspectives are given for further integrated investigation of key targets to address the internal structure and evolution of the Lesser Antilles Arc and Guadeloupe volcanic system.
Colloque 2012 du Comité National Français de Géodésie et Géophysique (CNFGG)
Clermont-Ferrand, France

hal-00742653
https://hal-brgm.archives-ouvertes.fr/hal-00742653
https://hal-brgm.archives-ouvertes.fr/hal-00742653/document
https://hal-brgm.archives-ouvertes.fr/hal-00742653/file/CNFGG_Caraibes.pdf

Éditeur(s) : HAL CCSD American Geophysical Union (AGU) American Geophysical Union
Résumé : International audience
GPS data reveal that the Brahmaputra Valley has broken from the Indian Plate and rotates clockwise relative to India about a point a few hundred kilometers west of the Shillong Plateau. The GPS velocity vectors define two distinct blocks separated by the Kopili fault upon which 2–3 mm/yr of dextral slip is observed: the Shillong block between longitudes 89 and 93°E rotating clockwise at 1.15°/Myr and the Assam block from 93.5°E to 97°E rotating at ≈1.13°/Myr. These two blocks are more than 120 km wide in a north-south sense, but they extend locally a similar distance beneath the Himalaya and Tibet. A result of these rotations is that convergence across the Himalaya east of Sikkim decreases in velocity eastward from 18 to ≈12 mm/yr and convergence between the Shillong Plateau and Bangladesh across the Dauki fault increases from 3 mm/yr in the west to >8 mm/yr in the east. This fast convergence rate is inconsistent with inferred geological uplift rates on the plateau (if a 45°N dip is assumed for the Dauki fault) unless clockwise rotation of the Shillong block has increased substantially in the past 4–8 Myr. Such acceleration is consistent with the reported recent slowing in the convergence rate across the Bhutan Himalaya. The current slip potential near Bhutan, based on present-day convergence rates and assuming no great earthquake since 1713 A.D., is now ~5.4 m, similar to the slip reported from alluvial terraces that offsets across the Main Himalayan Thrust and sufficient to sustain a Mw ≥ 8.0 earthquake in this area.
ISSN: 0148-0227

hal-01115084
https://hal.archives-ouvertes.fr/hal-01115084
DOI : 10.1002/2014JB011196

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : International audience
Guadeloupe island (West French Indies) is one of the twenty islands that compose the Lesser Antilles arc, which results from the subduction of the Atlantic ocean plate beneath the Caribbean one. The island lies in a complex volcano-tectonic system and the need to understand its geological context has led to numerous on- and offshore geophysical investigations. This work presents a compilation and the processing of available, on-land, airborne and marine, gravity and magnetic data acquired during the last 40 years on Guadeloupe islands and at the scale of the Lesser Antilles arc. The overall dataset provides new Bouguer and reduced to the pole magnetic anomaly maps at the highest achievable resolution. Regionally, the main central negative gravity trend of the arc allows defining two subsident areas. The first one is parallel to the arc direction (~N160°E) to the north, whereas the second unexpected southern one is oriented parallel to oceanic ridges (N130°E). Along the Outer arc, the long wavelength positive anomaly is interpreted, at least along the Karukera spur, as an up-rise of the volcanic basement in agreement with the seismic studies. To the NE of Guadeloupe, the detailed analysis of the geophysical anomalies outlines a series of structural discontinuities consistent with the main bathymetric morphologies, and in continuity of the main fault systems already reported in this area. Based on geophysical evidences, this large scale deformation and faulting of the Outer arc presumably primarily affects the Atlantic subducting plate and secondarily deforms the upper Caribbean plate and the accretion prism, as evidenced in bathymetry as well as on the islands. At the scale of Guadeloupe island, combined gravity and magnetic modeling has been initiated based on existing interpretation of old seismic refraction profiles, with a general structure in three main layers. According to our geophysical anomalies, additional local structures are also modeled in agreement with geological observations: i) the gravity and magnetic signals confirm an up-rise of the volcanic basement below the limestone platforms outcropping on Grande-Terre island ; ii) the ancient volcanic complexes of Basse-Terre island are modeled with high density and reverse magnetized formations; iii) the recent volcanic centre is associated with formations consistent with the low measured density and the underlying hydrothermal system. The E-W models coherently image a NNW-SSE depression structure in half-graben beneath Basse-Terre island, its western scarp following the arc direction in agreement with bathymetric and seismic studies to the north of the island. The so-defined depressed area, and particularly its opening in half-graben toward the SW, is interpreted as the present-day front of deformation of the upper plate, associated with the recent volcanic activity on and around Guadeloupe. Based on this regional deformation model, perspectives are given for further integrated investigation of key targets to address the internal structure and evolution of the Lesser Antilles arc and Guadeloupe volcanic system.
EISSN: 1777-5817

hal-00853352
https://hal.archives-ouvertes.fr/hal-00853352
DOI : 10.2113/gssgfbull.184.1-2.77

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : We use InSAR to measure deformation and kinematics of the Mw = 4.9 Borujerd (2005/05/03) and Mw = 6.1 Chalan-Chulan (2006/03/31) earthquakes that occurred in the Zagros fold-and-thrust belt. The focal mechanism of the 2006 event is consistent with right lateral strike-slip motion and the event ruptured the Dorud-Borujerd segment of the Main Recent Fault. An Envisat interferogram spanning the 2006 event shows peak ground deformation of 9 cm in the satellite line-of-sight along a 10 km long fault portion. The interferogram spanning the 2005 earthquake is rather related to atmospheric artefact than to ground deformation. Dislocation models of the 2006 Chalan-Chulan event indicate dextral slip amounting to a maximum of 90 cm at a depth of 4 km. The predicted vertical displacements are in good agreement with differential levelling data. The 2006 event filled only a small part of the seismic gap located between large M = 7 events that occurred in 1909 and 1957.
ISSN: 0954-4879

hal-00411313
https://hal.archives-ouvertes.fr/hal-00411313
DOI : 10.1111/j.1365-3121.2008.00797.x

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Northwest Iran is characterized by a high level of historical and instrumental seismicity related to the ongoing convergence between the Arabian and Eurasian plates. In this region, the main right-lateral strike-slip fault known as the North Tabriz fault (NTF) forms the central portion of a large crustal fault system called the Tabriz fault system (TFS). The NTF is a major seismic source along which at least three strong and destructive earthquakes have occurred since 858 AD. The two most recent destructive seismic events occurred in 1721 AD and 1780 AD, rupturing the SE and NW fault segments, respectively. This paper reports paleoseismological and quantitative geomorphologic investigations on the SE segment of the NTF, between the cities of Bostanabad and Tabriz. These observations help to improve our understanding of the seismic hazard for Tabriz city and its surrounding areas. Our field investigations revealed evidence of successive faulting events since the Late Quaternary. Paleoseismic investigations indicate that since 33.5 kyr, the SE segment of the NTF has experienced at least three major (M>7.5) seismic events, including the 1721 AD earthquake (M=7.6–7.7). Along the NW segment of the fault, however, our results suggest that the amount of strong (M~7.5) seismic events during the same period is significantly greater than along the SE segment. One possible explanation of such a difference in seismic activity is that the Late Quaternary-Holocene coseismic slip rate is decreasing along the NTF from the northwest to the southeast. This explanation contradicts the former hypothesis of a constant slip rate along the whole length of the NTF. In addition, more distributed deformation along several parallel fault branches, in a wider fault zone of the SE segment of the NTF may be considered as additional evidence for the estimation of lower rate of deformation along the fault segment. Such a slip distribution pattern can explain the existence of smaller (~300 m) Pliocene-Quaternary cumulative dextral offsets along the SE fault segment than the measured cumulative offsets along the NW segment (~800 m) of the NTF.
ISSN: 0040-1951

hal-01089420
http://hal.upmc.fr/hal-01089420
http://hal.upmc.fr/hal-01089420/document
http://hal.upmc.fr/hal-01089420/file/Solaymani%20Azad%20et%20al.%2C%202014%20%28accepted%29.pdf
DOI : 10.1016/j.tecto.2014.11.010

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Karukéra spur is an easternmost submerged rise of the Lesser Antilles fore-arc in the Guadeloupe archipelago, culminating about 4000 m above the fore-arc basin 150 km west of the deformation front. The analysis of 3500 km 2D high-resolution multichannel seismic reflection and multibeam bathymetric data, and the study of 14 core samples, allow for the first time to reconstruct its sedimentary anatomy and tectonic evolution. Seven seismic units (US1 to US7) are evidenced, organised into four major depositional sequences separated by erosional surfaces. Units US1 to US4 thicken to the south-southeast on the spur. The sedimentary deposits rest upon a deeply eroded metamorphic basement of the Caribbean Plate as in La Désirade Island. Sequence 1 (units US1 and US2) remains unknown in its lower part because it does not outcrop. Its upper part comprises early Miocene shallow water carbonates. Sequence S2 (Unit US3) only comprises an upper Miocene transgressive systems tract deposited into basinal environment. It is bounded by major erosional surfaces SB2 and SB3. Sequence 3 (US4 to US6) is Zanclean to Pleistocene. It is dominantly composed of shallow water, reefal deposits. Sequence 4 corresponds to recent deposits. The Karukéra spur experienced three main extensional episodes with alternations between uplift and subsidence periods. Uplifts are responsible for emersions and erosions. Subsidence severely drowned shallow water deposits. The first extensional episode led to the formation of horsts and grabens in the basement, prior to early Miocene deposits. The second extensional episode occurred during upper Miocene, in accordance with data in surrounding islands. The third tectonic episode developed since Calabrian. Noticeable is the constant reactivation of N130°–N150°, N150°–N180° and N40° trending faults since early Miocene and the neoformation of E–W trending faults since Calabrian. Our results suggest that at the latitude of Guadeloupean archipelago the Lesser Antilles subduction zone is an erosional margin because of the successive sweepings of the Santa Lucia then Tiburon Ridges.
ISSN: 0025-3227

hal-01172231
https://hal.archives-ouvertes.fr/hal-01172231
DOI : 10.1016/j.margeo.2015.02.007

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
Recent field work and review of radiometric data obtained from Neogene lavas and plutonic rocks exposed in the Eastern Central Patagonian Cordillera (46–48ºS), which overlie subducted segments of the South Chile Ridge, suggest important Late Miocene to Pleistocene morphological changes in relation to base level variations and/or tectonic events. We present new field observations from a region south of Lago General Carrera-Buenos Aires, between the main Cordillera and the Meseta del Lago Buenos Aires, demonstrating that normal faulting controlled valley incisions and occurred during lava emplacement at 5–4 Ma and after 3 Ma. We also show that the 12 Ma basaltic flows of the Meseta del Lago Buenos Aires (~2000 m a.s.l.) have been subjected to deep incision, with younger lavas dated at 1.2 Ma partially filling the valleys. These incisions are thought to reflect progressive eastward tilting of the entire meseta. Our new observations, together with additional features from Central Patagonia, strongly suggest that tectonic events led to a regional widespread morphological change after 5 Ma. The coincidence in time and space between the subduction of segments of the South Chile Ridge at 6 and 3 Ma causing opening of a slab window, and strong base level variations in the studied area, suggests a cause-and-effect relationship. In Central Patagonia, compressional tectonics ended well before extensional events reported here. Causes of uplift and further extension are probably completely disconnected. The uplift is purely tectonic in origin and occurred prior to the subduction of the South Chile Ridge. Extension should be a consequence of this subduction.
ISSN: 0954-4879

insu-00272075
https://hal-insu.archives-ouvertes.fr/insu-00272075
DOI : 10.1111/j.1365-3121.2007.00766.x

Éditeur(s) : HAL CCSD
Résumé : To study the dynamics of an orogen-foreland system and more particularly the impact of surface processes on its development, we base our work on two main axes. In a first part, using analogue tapered wedge models, we investigate the interplay between tectonics, erosion and sedimentation during the orogenic growth. The basis model mimics the evolution of a wedge section extending from the orogen to its foreland basin, with both the structural and the lithological heritages simulated. In a second part, the focus is on the recent tectonic and geomorphologic processes affecting the Swiss Prealpes klippen belt and surrounding structural units (Molasse basin and Jura fold-and-thrust belt). Remote sensing analyses allow to evaluate the impact of tectonics on the drainage pattern and landscape morphology. In addition, local field investigations in the Prealpes provide information on the nature and kinematic of brittle fractures and the paleostress fields.
Afin d'étudier la dynamique d'un système orogène/avant-pays et plus particulièrement l'impact des processus de surface sur son développement, notre travail se base sur deux axes principaux. Dans une première partie, à l'aide de modèles analogiques de prisme d'accrétion, nous analysons les interactions entre la tectonique, l'érosion et la sédimentation au cours de la croissance de l'orogène. Le modèle de base reproduit l'évolution d'une section de prisme, qui s'étend de l'orogène au bassin d'avant-pays, et où les héritages à la fois structural et lithologique sont simulés. Dans une seconde partie, l'accent est mis sur la tectonique récente et les processus géomorphologiques qui affectent la klippe des Préalpes suisses et les unités structurales environnantes (le bassin molassique et le Jura). Des analyses de télédétection permettent d'évaluer l'influence de la tectonique sur le réseau de drainage et la morphologie du paysage. De plus, des analyses de terrain menées localement dans les Préalpes fournissent des informations sur la nature et la cinématique des fractures cassantes et des champs de paléocontraintes.
https://tel.archives-ouvertes.fr/tel-00138836

tel-00138836
https://tel.archives-ouvertes.fr/tel-00138836
https://tel.archives-ouvertes.fr/tel-00138836/document
https://tel.archives-ouvertes.fr/tel-00138836/file/These_Bonnet_2007.pdf