Éditeur(s) : Elsevier
Résumé : We present new results from the MARADJA'03 cruise depicting the geological structures offshore central and western Algeria. Using swath bathymetry and seismic reflection data, we map and discuss the offshore limits of the Internal Zones corresponding to relics of the AIKaPeCa domain that drifted and collided the African plate during the Miocene. We identify large reverse faults and folds that reactivate part of these limits and are still active today. The morphology of the westernmost NE-SW margin suggests a former strike-slip activity accommodating a westward block translation responsible for the shift of the Internal Zones towards the Moroccan Rif.
Nous présentons les résultats récents de la campagne MARADJA'03, qui visent à mettre en évidence les structures géologiques dans le domaine marin au nord-ouest de l'Algérie. Grâce aux données de bathymétrie multifaisceau et de sismique réflexion, nous cartographions et discutons les limites en mer des Zones internes correspondant aux reliques du domaine AlKaPeCa qui a dérivé, puis est entré en collision avec la plaque africaine au Miocène. De grandes failles inverses et plis, actifs dans le champ de contrainte actuel, réactivent certaines de ces limites. La marge ouest-algérienne, orientée NE¿SW, indique la présence d'une ancienne activité en décrochement ayant accommodé la translation des Zones internes vers l'ouest.
Comptes Rendus Geoscience (1631-0713) (Elsevier), 2006 , Vol. 338 , N. 1-2 , P. 80-91

Droits : 2005 Académie des sciences Published by Elsevier SAS
http://archimer.ifremer.fr/doc/2006/publication-1211.pdf
DOI:10.1016/j.crte.2005.11.009
http://archimer.ifremer.fr/doc/00000/1211/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We present evidence that GPS velocity estimates of plate motions and fault slip rates agree to within uncertainties with geologic estimates during the most recent phase of the geologic evolution of the E Mediterranean region (post-Late Miocene). On this basis, we use the GPS differential velocities to estimate the timing of initiation of the principal structures in NW Turkey, the N Aegean Sea, and central Greece, including, the Marmara Sea, the Gulfs of Evia (GoE) and Corinth (GoC). and the Kephalonia Transform fault (KTF). We interpret these ages to indicate that the North Anatolian fault propagated across the N Aegean, opening the GoE and GoC and initiating the KTF, during the past 1-4 Ma. We further suggest that Aegean extension that was earlier more distributed across the Aegean Basin became focused on this new fault system allowing the southern Aegean and Peloponnisos to translate SW with little internal deformation, as observed today with GPS. This change in tectonic configuration may account for the clear geologic evidence for crustal thinning throughout the S Aegean in apparent contradiction with low present-day strain rates. We further show that the low present-day strain rate along the southern edge of the Aegean micro-plate requires substantial aseismic slip along the plate interface below Crete, consistent with the low level of historic, subduction-type earthquakes along this segment of the subduction zone.
ISSN: 0040-1951

hal-00512634
https://hal.archives-ouvertes.fr/hal-00512634
DOI : 10.1016/j.tecto.2009.05.027

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We develop a block model for the Aegean and surrounding areas, constrained by Global Positioning System (GPS), in order to investigate the degree of coupling on the Hellenic subduction interface (i.e., the fraction of the motion across the plate boundary accommodated by elastic strain accumulation). We use previously published models, and seismicity to define the geometry of the interface separating the down-going Nubian slab from the overriding Aegean. This model provides a good fit to the GPS observations; for the ∼200,000 km2 Aegean block the wrms of the residual velocities is 1.4 mm/yr for 80 GPS velocity estimates, approximately the 95% level of the GPS velocity uncertainties. We investigate the degree of coupling on the seismically active plate interface, the Hellenic trench splay fault (believed to be the source of the 365 AD Great Crete Earthquake and Tsunami), and the Kephalonia transform fault by comparing the modeled GPS residual velocity field for a range of coupling values. The GPS observations are almost insensitive to coupling on the Kephalonia transform fault, because of the vertical dip of the fault that creates interseismic deformation only close to the fault where few GPS sites exist. The absence of resolvable shortening of the leading edge of the Aegean Plate precludes coupling of more than 0.2 (20% of the full Nubia-Aegean convergence rate) on the modeled plate interface. Because of the shallow dip of the plate interface and trench splay fault, and high rate of convergence, if these boundaries were fully coupled, high elastic strain rates would be expected to extend well into the overriding Aegean plate. Based on our preferred value for the degree of coupling (0.1), and assuming characteristic earthquake behavior, we estimate a recurrence time for great earthquakes with slip similar to that for the 365 Crete event of 5700-8300 yr, consistent with the absence of subsequent great earthquakes on this segment of the subduction zone.
ISSN: 0012-821X

hal-01053486
https://hal.archives-ouvertes.fr/hal-01053486
DOI : 10.1016/j.epsl.2013.10.018

Éditeur(s) : HAL CCSD Oxford University Press (OUP): Policy P - Oxford Open Option A Oxford University Press (OUP)
Résumé : International audience
While the kinematics of Anatolia plate and the North Anatolian Fault System (NAFS) has been studied extensively, the slip rate and locking depth along the NAFS are usually assumed constant in the analyses due to the lack of sufficient data. This is also partly due to the reasonably good fit of Euler small circle and partly due to the lack of spatial resolution of observations to determine slip rates independently from locking depths. On the other hand, recent geodetic studies show a contrast for locking depth between Marmara and other parts of the NAFS, implying a non-uniform locking depth across the NAFS. In this study, we analyse new GPS data and homogenously combine available data sets covering the eastern part of the NAFS to form the most complete data set. In particular, we incorporate the first results of Turkish Real-Time Kinematic GPS Network (CORS-TR) into our data set. A detailed analysis of three profiles within the NAFS reveals an increase of locking depth in the middle profile to 19.1 ± 3.4 km from 11.9 ± 3.5 km in the easternmost profile while the slip rate is nearly constant (20–22 mm yr−1), which implies a variation of strain rate of ∼100 nanostrain yr−1. Assuming a constant locking depth throughout whole NAFS gives an average locking depth of 14.3 ± 1.7 km. Our best estimates of slip rates in block modelling which takes the variation of locking depths into account are in the range between 22.5 and 22.8 mm yr−1 over eastern part of the NAFS.
ISSN: 0956-540X

hal-01218392
https://hal.archives-ouvertes.fr/hal-01218392
DOI : 10.1093/gji/ggv274