Papers by Philippe Vernant
Geophysical Journal International, Mar 1, 2007
Approximately 4 yr of campaign and continuous Global Positioning System (GPS) measurements across... more Approximately 4 yr of campaign and continuous Global Positioning System (GPS) measurements across the Dead Sea fault system (DSFS) in Lebanon provide direct measurements of interseismic strain accumulation along a 200-km-long restraining bend in this continental transform fault. Late Cenozoic transpression within this restraining bend has maintained more than 3000 m of topography in the Mount Lebanon and Anti-Lebanon ranges. The GPS velocity field indicates 4-5 mm yr −1 of relative plate motion is transferred through the restraining bend to the northern continuation of the DSFS in northwestern Syria. Near-field GPS velocities are generally parallel to the major, left-lateral strike-slip faults, suggesting that much of the expected convergence across the restraining bend is likely accommodated by different structures beyond the aperture of the GPS network (e.g. offshore Lebanon and, possibly, the Palmyride fold belt in SW Syria). Hence, these geodetic results suggest a partitioning of crustal deformation involving strike-slip displacements in the interior of the restraining bend, and crustal shortening in the outer part of the restraining bend. Within the uncertainties, the GPS-based rates of fault slip compare well with Holocene-averaged estimates of slip along the two principal strike-slip faults: the Yammouneh and Serghaya faults. Of these two faults, more slip occurs on the Yammouneh fault, which constitutes the primary plate boundary structure between the Arabia and Sinai plates. Hence, the Yammouneh fault is the structural linkage that transfers slip to the northern part of the transform in northwestern Syria. From the perspective of the regional earthquake hazard, the Yammouneh fault is presently locked and accumulating interseismic strain.
AGU Fall Meeting Abstracts, Dec 1, 2016
AGUFM, Dec 1, 2004
(Presented on behalf of the E. Med/Caucasus GPS Consortium). We use GPS observations during the p... more (Presented on behalf of the E. Med/Caucasus GPS Consortium). We use GPS observations during the period 1988 to 2004 to constrain an elastic block model for deformation within the zone of interaction of the Eurasian, African, and Arabian plates. We constrain present-day motions of the African (Nubian), Arabian, and Eurasian plates, regional deformation within the inter-plate zone, and slip rates
EGU General Assembly Conference Abstracts, Apr 1, 2017
EGU General Assembly Conference Abstracts, Apr 1, 2009
GPS measurements adjacent to the southern Red Sea and around the Afar Triple Junction (Red Sea Ri... more GPS measurements adjacent to the southern Red Sea and around the Afar Triple Junction (Red Sea Rift-Gulf of Aden Rift-East African Rift), indicate that the Red Sea rift bifurcates south of 16°N latitude with one branch following a continuation of the main Red Sea rift (∼150°Azimuth) and the other oriented roughly N-S traversing the Danakil Depression/Afar volcanic province. These two rift branches account for the full Arabia-Nubia relative motion. Within the resolution of our observations, the partitioning of extension between rift branches varies linearly along strike; north of ∼16°N extension (∼15 mm/yr at 16°N) is confined to the main Red Sea rift while at the latitude of the Afar Triple Junction (∼12°N) extension (∼20 mm/yr) has transferred completely to the Danakil-Afar Depression. The Danakil block separates the two rifts and rotates counterclockwise, accommodating extension along the rifts and developing the triangular geometry of the Danakil/Afar Depression. Extrapolating the geodetic rates to the time of initial rifting of Arabia from Nubia (∼25 ± 3 Ma) and estimating total extension across the rift branches from the present-day widths of the rifts suggests that Arabia-Nubia relative motion has been roughly constant since the initiation of Red Sea spreading, and that extension was initially confined to the main Red Sea rift with the presently observed bifurcation initiating at about 17 Ma.
EGU General Assembly Conference Abstracts, Apr 1, 2016
AGUFM, Dec 1, 2005
ABSTRACT [ 1] The GPS-derived velocity field ( 1988 - 2005) for the zone of interaction of the Ar... more ABSTRACT [ 1] The GPS-derived velocity field ( 1988 - 2005) for the zone of interaction of the Arabian, African ( Nubian, Somalian), and Eurasian plates indicates counterclockwise rotation of a broad area of the Earth's surface including the Arabian plate, adjacent parts of the Zagros and central Iran, Turkey, and the Aegean/Peloponnesus relative to Eurasia at rates in the range of 20 - 30 mm/yr. This relatively rapid motion occurs within the framework of the slow-moving ( similar to 5 mm/yr relative motions) Eurasian, Nubian, and Somalian plates. The circulatory pattern of motion increases in rate toward the Hellenic trench system. We develop an elastic block model to constrain present-day plate motions ( relative Euler vectors), regional deformation within the interplate zone, and slip rates for major faults. Substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below similar to 1 - 2 mm/yr, including central and eastern Anatolia ( Turkey), the southwestern Aegean/ Peloponnesus, the Lesser Caucasus, and Central Iran. Geodetic slip rates for major block-bounding structures are mostly comparable to geologic rates estimated for the most recent geological period ( similar to 3 - 5 Myr). We find that the convergence of Arabia with Eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the Caucasus and Zagros mountain belts around the periphery of the collision zone. In addition, we find that the principal boundary between the westerly moving Anatolian plate and Arabia ( East Anatolian fault) is presently characterized by pure left-lateral strike slip with no fault-normal convergence. This implies that "extrusion'' is not presently inducing westward motion of Anatolia. On the basis of the observed kinematics, we hypothesize that deformation in the Africa-Arabia-Eurasia collision zone is driven in large part by rollback of the subducting African lithosphere beneath the Hellenic and Cyprus trenches aided by slab pull on the southeastern side of the subducting Arabian plate along the Makran subduction zone. We further suggest that the separation of Arabia from Africa is a response to plate motions induced by active subduction.
HAL (Le Centre pour la Communication Scientifique Directe), Nov 15, 2021
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
2014 AGU Fall Meeting, Dec 19, 2014
2014 AGU Fall Meeting, Dec 19, 2014
. In regions formerly glaciated during the Last Glacial Maximum (LGM), Glacial Isostatic Adjustme... more . In regions formerly glaciated during the Last Glacial Maximum (LGM), Glacial Isostatic Adjustment (GIA) explains most of the measured uplift and deformation rates. GIA is also proposed as a key process contributing to fault activity and seismicity shortly after the LGM and potentially up to present-day. Here, we study the impact of GIA on present-day fault activity and seismicity in the Western Alps. We show that, in the upper crust, GIA induces horizontal compressive stress perturbations associated with horizontal extension rates. The latter agree with the observed geodetic strain rates and with the seismicity deformation patterns. Yet, in nearly all cases, the GIA stress perturbations tend either to inhibit fault slip, or to promote fault slip with the wrong mechanism compared to the seismicity deformation style. Thus, although GIA from the LGM explains a major part of the geodetic strain rates, it does not drive nor promote the observed seismicity (which must be driven by other processes). This apparent strain rate - stress paradox results from the gradual diminution over time of the finite shortening induced in the upper crust by the LGM icecap. A direct corollary of our results is that seismicity and seismic hazard studies in the Western Alps cannot directly integrate geodetic velocities and strain rates, but instead require detailed modeling of the GIA transient impact.
HAL (Le Centre pour la Communication Scientifique Directe), 2022
HAL (Le Centre pour la Communication Scientifique Directe), Jul 1, 2017
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
105 synthetic time series replicating GNSS 3D position series are analyzed independently by nine ... more 105 synthetic time series replicating GNSS 3D position series are analyzed independently by nine different groups within the RENAG consortium in order to characterize the variability in estimations of long-term velocities. The main objective is not a detailed study of the parameters and sources controlling velocity variations, but simply to establish first-order conclusions regarding the uncertainties on GNSS velocity estimations as a function of the different analysis methods and software. Because the true velocities are known, our results are presented in terms of velocity biases (i.e. deviations of the estimated velocities relative to the expected values). Statistics on these biases can then be used as indicators of the potential precision of actual GNSS velocities. To first order, the nine methods and software of time series analysis provide horizontal (resp. vertical) velocity estimations at precisions better than 1.0 mm/a (resp. 2.0 mm/a). None of the tested methods or softwar...
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Papers by Philippe Vernant