Paleoseismic History of the Dead Sea Fault Zone

International audienceThe aim of this entry is to describe the DSF as a transform plate boundary pointing out the rate of activedeformation, fault segmentation, and geometrical complexities as a control of earthquake ruptures. Thedistribution of large historical earthquakes from a revisited seismicity catalogue using detailedmacroseismic maps allows the correlation between the location of past earthquakes and fault segments.The recent results of paleoearthquake investigations (paleoseismic and archeoseismic) with a recurrenceinterval of large events and long-term slip rate are presented and discussed along with the identification ofseismic gaps along the fault. Finally, the implications for the seismic hazard assessment are also discussed

In-situ evidence for dextral active motion at the Arabia-India plate boundary

International audienceThe Arabia-India plate boundary--also called theOwen fracture zone--is perhaps the least-known boundary among large tectonic plates1-6. Although it was identified early on as an example of a transform fault converting the divergent motion along the Carlsberg Ridge to convergent motion in the Himalayas7, its structure and rate of motion remains poorly constrained. Here we present the first direct evidence for active dextral strike-slip motion along this fault, based on seafloor multibeam mapping of the Arabia-India-Somalia triple junction in the northwest Indian Ocean. There is evidence for 12km of apparent strike-slip motion along the mapped segment of the Owen fracture zone, which is terminated to the south by a 50-km-wide pull-apart basin bounded by active faults. By evaluating these new constraints within the context of geodetic models of global plate motions, we determine a robust angular velocity for the Arabian plate relative to the Indian plate that predicts 2-4mmyr−1 dextral motion along the Owen fracture zone. This transformfault was probably initiated around 8 million years ago in response to a regional reorganization of plate velocities and directions8-11, which induced a change in configuration of the triple junction. Infrequent earthquakes of magnitude 7 and greater may occur along the Arabia-India plate boundary, unless deformation is in the formof aseismic creep

Seven years of postseismic deformation following the 1999, M = 7.4 and M = 7.2, Izmit-Duzce, Turkey earthquake sequence

We report the results of nearly 7 years of postseismic deformation measurements using continuously recorded and survey mode GPS observations for the 1999 Izmit-Düzce earthquake sequence. Resolvable, time-dependent postseismic changes to the preearthquak

Seven years of postseismic deformation following the 1999, M = 7.4 and M = 7.2, Izmit-Düzce, Turkey earthquake sequence

We report the results of nearly 7 years of postseismic deformation measurements using continuously recorded and survey mode GPS observations for the 1999 Izmit-Düzce earthquake sequence. Resolvable, time-dependent postseismic changes to the preearthquake interseismic velocity field extend at least as far as the continuous GPS station in Ankara, ∼200 km southeast of the Izmit rupture. Seven years after the earthquake sequence, the relative postseismic velocity across the North Anatolian Fault (NAF) reaches ∼10–12 mm/a, roughly 50% of the steady state interseismic rate, with the highest postseismic velocities within 40 km of the coseismic ruptures. We use a sequence of logarithmic time functions to fit GPS site motions. Up to three logarithmic terms with decay constants of 1, 150, and 3500 days are necessary to fit all the transient motion observed at the continuous GPS stations. The first term is required for the component of site motion parallel to the NAF at near-field sites strongly implicating rapid, shallow afterslip. The intermediate and longer-term postseismic velocity components reflect more broadly distributed strain with a symmetric double-couple pattern suggestive of either localized, deep afterslip or viscoelastic relaxation of the upper mantle and/or lower crust. In two areas (including the Marmara Sea) this pattern is superimposed on north-south extension centered on the NAF. We speculate that this extension may result from aseismic dip slip along coseismically weakened faults, driven by the background tectonic stress.Scientific and Technological Research Council of Turkey (CAYADAG Project 103Y100, EU 6)European Training Foundation (Frame FORESIGHT Project contract 511139)Scientific and Technological Research Council of Turkey (TARAL 1007 Project 105G019)National Science Foundation (U.S.) (grant EAR-0337497)National Science Foundation (U.S.) (grant EAR-0305480)National Science Foundation (U.S.) (grant INT-0001583)Natural Sciences and Engineering Research Council of Canada (Discovery grant RGPIN 261 458-07