Shallow architecture of the Wadi Araba fault (Dead Sea Transform) from high-resolution seismic investigations (original) (raw)
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Seismic structure of the Arava Fault, Dead Sea Transform
2004
The Dead Sea Transform (DST) is a prominent shear zone in the Middle East. It separates the Arabian plate from the Sinai microplate and stretches from the Red Sea rift in the south via the Dead Sea to the Taurus-Zagros collision zone in the north. Formed in the Miocene 17 Ma ago and related to the breakup of the Afro-Arabian continent, the DST accommodates the left-lateral movement between the two plates. The study area is located in the Arava Valley between the Dead Sea and the Red Sea, centered across the Arava Fault (AF), which constitutes the major branch of the transform in this region. A set of seismic experiments comprising controlled sources, linear profiles across the fault, and specifically designed receiver arrays reveals the subsurface structure in the vicinity of the AF and of the fault zone itself down to about 3-4 km depth. A tomographically determined seismic P velocity model shows a pronounced velocity contrast near the fault with lower velocities on the western side than east of it. Additionally, S waves from local earthquakes provide an average P-to-S velocity ratio in the study area, and there are indications for a variations across the fault. High-resolution tomographic velocity sections and seismic reflection profiles confirm the surface trace of the AF, and observed features correlate well with fault-related geological observations. Coincident electrical resistivity sections from magnetotelluric measurements across the AF show a conductive layer west of the fault, resistive regions east of it, and a marked contrast near the trace of the AF, which seems to act as an impermeable barrier for fluid flow. The correlation of seismic velocities and electrical resistivities lead to a characterisation of subsurface lithologies from their physical properties. Whereas the western side of the fault is characterised by a layered structure, the eastern side is rather uniform. The vertical boundary between the western and the eastern units seems to be offset to the east of the AF surface trace. A modelling of fault-zone reflected waves indicates that the boundary between low and high velocities is possibly rather sharp but exhibits a rough surface on the length scale a few hundreds of metres. This gives rise to scattering of seismic waves at this boundary. The imaging (migration) method used is based on array beamforming and coherency analysis of P-to-P scattered seismic phases. Careful assessment of the resolution ensures reliable imaging results. The western low velocities correspond to the young sedimentary fill in the Arava Valley, and the high velocities in the east reflect mainly Precambrian igneous rocks. A 7 km long subvertical scattering zone (reflector) is offset about 1 km east of the AF surface trace and can be imaged from 1 km to about 4 km depth. The reflector marks the boundary between two lithological blocks juxtaposed most probably by displacement along the DST. This interpretation as a lithological boundary is supported by the combined seismic and magnetotelluric analysis. The boundary may be a strand of the AF, which is offset from the current, recently active surface trace. The total slip of the DST may be distributed spatially and in time over these two strands and possibly other faults in the area.
The rift-like structure and asymmetry of the Dead Sea Fault
Earth and Planetary Science Letters, 2010
Whereas the Dead Sea Fault is a major continental transform, active since ca. 13-18 Ma ago, it has a rift-like morphology along its southern part. It has been argued that this results from a transtensional component active since 5 Ma ago, due to a regional plate kinematics change. We present the results of 3D laboratory experiments carried out to test this hypothesis and to explore its consequences for the structure and morphology of the Dead Sea Fault. We conclude that a two-stage tectonic history invoking a first stage of pure strike-slip and a second stage marked by the addition of a minor transtensional component is consistent with most of the striking geological and geophysical features of the Dead Sea Fault. The structural and morphological asymmetry of the Dead Sea Fault can be explained by a transverse horizontal shear in the ductile lower crust below the transform zone. A large-scale heating event of the Arabian mantle is not required to explain these features of the Dead Sea Fault.
Journal of Seismology, 2006
The archaeological site of Qasr Tilah, in the Wadi Araba, Jordan is located on the northern Wadi Araba fault segment of the Dead Sea Transform. The site contains a Roman-period fort, a late Byzantine–Early Umayyad birkeh (water reservoir) and aqueduct, and agricultural fields. The birkeh and aqueduct are left-laterally offset by coseismic slip across the northern Wadi Araba fault. Using paleoseismic and archaeological evidence collected from a trench excavated across the fault zone, we identified evidence for four ground-rupturing earthquakes. Radiocarbon dating from key stratigraphic horizons and relative dating using potsherds constrains the dates of the four earthquakes from the sixth to the nineteenth centuries. Individual earthquakes were dated to the seventh, ninth and eleventh centuries. The fault strand that slipped during the most recent event (MRE) extends to just below the modern ground surface and juxtaposes alluvial-fan sediments that lack in datable material with the modern ground surface, thus preventing us from dating the MRE except to constrain the event to post-eleventh century. These data suggest that the historical earthquakes of 634 or 659/660, 873, 1068, and 1546 probably ruptured this fault segment.
Detailed seismicity analysis revealing the dynamics of the southern Dead Sea area
Journal of Seismology, 2014
Within the framework of the international DESIRE (DEad Sea Integrated REsearch) project, a dense temporary local seismological network was operated in the southern Dead Sea area. During 18 recording months, 648 events were detected. Based on an already published tomography study clustering, focal mechanisms, statistics and the distribution of the microseismicity in relation to the velocity models from the tomography are analysed. The determined b value of 0.74 leads to a relatively high risk of large earthquakes compared to the moderate microseismic activity. The distribution of the seismicity indicates an asymmetric basin with a vertical strike-slip fault forming the eastern boundary of the basin, and an inclined western boundary, made up of strike-slip and normal faults. Furthermore, significant differences between the area north and south of the Bokek fault were observed. South of the Bokek fault, the western boundary is inactive while the entire seismicity occurs on the eastern boundary and below the basin-fill sediments. The largest events occurred here, and their focal mechanisms represent the northwards transform motion of the Arabian plate along the Dead Sea Transform. The vertical extension of the spatial and temporal cluster from February 2007 is interpreted as being related to the locking of the region around the Bokek fault. North of the Bokek fault similar seismic activity occurs on both boundaries most notably within the basin-fill sediments, displaying mainly small events with strike-slip mechanism and normal faulting in EW direction. Therefore, we suggest that the Bokek fault forms the border between the single transform fault and the pull-apart basin with two active border faults.
Active tectonics along the Wadi Araba-Jordan Valley transform fault
Journal of Geophysical Research, 1999
A geological study has been carried out along the 200 km long Wadi Araba following the transform fault that separates the Arabian and Sinai-African Plates. Recent movements along this structure affect upper Pleistocene-Holocene deposits and archaeological sites. Kinematic indicators show sinistral strike-slip and oblique movements, in agreement with the relative motion between the two plates. Other evidence of recent horizontal displacement exists along the Jordan Valley Fault, both on the Dead Sea-Lake Tiberias segment and on the segment north of Lake Tiberias. A minimum horizontal slip rate of 1 cm yr-• has been estimated for both the southern segment of the Wadi Araba Fault and for the southern Jordan River Fault. The two faults can be roughly subdivided into at least four segments: two in the Wadi Araba (80 km long each), one from the Dead Sea to Lake Tiberias (130 km), and one from Lake Tiberias to the Hula graben (>30 km). Faulting may also occur along shorter subsegments, as shown by bends in the Wadi Araba-Jordan River Fault and by the growth of local compression and extension features. Instrument-recorded seismicity appears to be mainly concentrated along some of these subsegments. A comparison between the observed seismic and field-determined slip rates across the fault indicates possible strain accumulation during the last 2000 years.
Marine and Petroleum Geology, 2006
Interpretation of recently released seismic reflection lines from the Shuna (Eastern Jericho) Basin combined with re-analysis of the lithologic logs of the deep JV-1 and JV-2 boreholes provide new insights into the structure of the sedimentary basin that formed along the Dead Sea Transform fault north of the Dead Sea in Jordan. We identified four major seismic boundaries in the reflection profiles. The upper two were correlated with borehole stratigraphy. These reflection boundaries include the top of the pan-African basement (R4), the base of the Mesozoic (R3), the base of the Cretaceous (R2), and the base of the post-Eocene section (R1). The latter records sedimentation during the Dead Sea Transform tectonic regime. The total thickness attained by the older sedimentary units (Late Cretaceous through Cambrian) is apparently less than 2 km. We identified a subsurface structure, a faulted monocline, with a N-S trend, sub-parallel to the strike of the Dead Sea Transform, that is named here Al Kharrar monocline. The Al Kharrar structural ensemble is buried by syntectonic lacustrine and fluviatile sediments of the Jordan Valley Group. The structure formed as part of the Dead Sea Transform deformation overprinting the Late Cretaceous Syrian arc folds. Continued tectonic deformation is evident from the prominent unconformity at the base of post-Eocene syntectonic deposits that dip NW, W and S away from the structural high. Along the NW-flank of the Al Kharrar monocline syntectonic sediment thickness is generally less than 0.5 km while along the SW-flank it thickens rapidly to nearly 1 km at the southern end of the interpreted seismic lines. This rapid southern subsidence probably continues into the north end of the Dead Sea Basin the lake's shoreline being located less than 3 km to the south. Young bifurcating faults with reverse slip components cutting the eastern part of the Al-Kharrar monocline are attributed to a positive flower structure. This pattern suggests strike slip with localized active compression northeast of the Dead Sea. It may result from local transpression between fault strands that appear to be a northward continuation of the eastern boundary fault of the Dead Sea Basin.
Fracturing patterns, stress fields and earthquakes in the Southern Dead Sea rift
Journal of Geodynamics, 2005
Integrated investigations including the structural analysis of shear fractures and fault zones, the reconstruction of stress fields and the fractal analysis of the epicentral field of recent earthquakes have been pursued in the Dead Sea rift. The N-S and NW-SE trending faults are very extensive and they display large zones of crushed rock compared with faults of other orientations. According to the fractal analysis of the seismicity over the period of 1983-2002 and a review of historical destructive earthquakes associated with faulting of archaeological sites, large N-S and NW-SE fault zones traced in different sites are the major structures that control the seismic activity in the southern part of the rift. Many of the N-S trending faults are well pronounced within the basins but they are not as frequent in the inter-basin link zones. Meso-structural features document normal fault displacements along the major faults within basins. In the uplifted inter-basin links the kinematics varies from normal to strike-slip faulting along the same fault zones. The NW-SE faults are characterized by normal and oblique displacement, the E-W faults by strike-slip displacements and the NE-SW faults by composite strike-slip and normal displacement. The tectonic stress fields reconstructed from shear fractures orientations show that two main types of local stress tensors are associated with the structural development of the Dead Sea rift: (1) tension with E-W (mainly) and ENE-WSW trending σ 3 and (2) transcurrent with NE-SW (sometimes nearly E-W) trending σ 3 and NW-SE (sometimes nearly N-S) trending σ 1. The comparison between the obtained data and analog models of structural systems formed under variable loading conditions indicates that the observed features and the inferred stress fields in the Dead Sea rift are typical to oblique extension settings.