Anatomy of the Dead Sea transform: Does it reflect continuous changes in plate motion? (original) (raw)
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The crustal structure of the Dead Sea Transform
2004
To address one of the central questions of plate tectonics – How do large transform systems work and what are their typical features? – seismic investigations across the Dead Sea Transform (DST), the boundary between the African and Arabian plates in the Middle East, were conducted for the first time. A major component of these investigations was a combined reflection/refraction survey across the territories of Palestine, Israel and Jordan. The main results of this study are: (1) The seismic basement is offset by 3-5 km under the DST, (2) The DST cuts through the entire crust, broadening in the lower crust, (3) Strong lower crustal reflectors are imaged only on one side of the DST, (4) The seismic velocity sections show a steady increase in the depth of the crust-mantle transition (Moho) from ~26 km at the Mediterranean to ~39 km under the Jordan highlands, with only a small but visible, asymmetric topography of the Moho under the DST. These observations can be linked to the left-lateral movement of 105 km of the two plates in the last 17 Myr, accompanied by strong deformation within a narrow zone cutting through the entire crust. Comparing the DST and the San Andreas Fault (SAF) system, a strong asymmetry in subhorizontal lower crustal reflectors and a deep reaching deformation zone both occur around the DST and the SAF. The fact that such lower crustal reflectors and deep deformation zones are observed in such different transform systems suggests that these structures are possibly fundamental features of large transform plate boundaries.
The Seismicity along the Dead Sea Fault during the Last 60,000 Years
Bulletin of The Seismological Society of America, 2009
Evidence for unchanging slip rate and a Gutenberg-Richter relation for earthquake distribution along the Dead Sea fault during the past 60,000 yr are presented. The evidence comes from three different segments, approximately 100 km apart, and from three different timescales: prehistoric-paleoseismic, historical, and modern (instrumental) records. The paleoseismic data are based on two different methods. In the southern Arava Valley and the northern Jordan Valley segments, the amount of normal displacement along several faults is used, while in the Dead Sea basin the appearance of brecciated beds, which are considered as seismites, is used. We found that for the southern Arava Valley segment a constant dip-slip rate of 0:5 mm=yr can explain the cumulative normal slip during the past 45,000 yr. This suggests that normal faulting is only ∼10% of the total left-lateral strike-slip motion. We also found that for all three segments, the paleoseismic and historical records of strong earthquakes lie on the linear extrapolation of the frequency-magnitude relation of the instrumental record. The calculated b-values for all three segments are between 0.85 and 1, similar to other major strike-slip faults in the world. It is concluded that the Gutenberg-Richter distribution is a stable mode in the tectonic setting of the Dead Sea fault during the past 60,000 yr. 2020
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.
Tectonophysics, 2002
The Dead Sea Basin is a morphotectonic depression along the Dead Sea Transform. Its structure can be described as a deep rhomb-graben (pull-apart) flanked by two block-faulted marginal zones. We have studied the recent tectonic structure of the northwestern margin of the Dead Sea Basin in the area where the northern strike-slip master fault enters the basin and approaches the western marginal zone (Western Boundary Fault). For this purpose, we have analyzed 3.5-kHz seismic reflection profiles obtained from the northwestern corner of the Dead Sea. The seismic profiles give insight into the recent tectonic deformation of the northwestern margin of the Dead Sea Basin. A series of 11 seismic profiles are presented and described.
We present new results from a paleoseismic trenching campaign at a site across the Jordan Gorge Fault (JGF), the primary strand of the Dead Sea Transform in northern Israel. In addition to the previously recognized earthquakes of 1202 and 1759 C.E., we observe evidence for eight surface-rupturing earthquakes prior to the second millennium C.E. The past millennium appears deficient in strain release with the occurrence of only two large ruptures, when compared with the preceding 1200 years. Assuming Gutenberg-Richter magnitude-frequency distribution, there is a discrepancy between measured rate of small-magnitude earthquakes (M < 4) from instrumental records and large earthquake rates from paleoseismic records. The interevent time of surface-rupturing earthquakes varies by a factor of two to four during the past 2 ka at our site, and the fault's behavior is not time predictable. The JGF may be capable of rupturing in conjunction with both of its southern and northern neighboring segments, and there is tentative evidence that earthquakes nucleating in the Jordan Valley (e.g., the 749 C.E. earthquake) could either rupture through the stepover between the faults or trigger a smaller event on the JGF. We offer a model of earthquake production for this segment in which the long-term slip rate remains constant while differing earthquake sizes can occur, depending on the segment from which they originated and the time since the last large event. The rate of earthquake occurrence in this model does not produce a time-predictable pattern over a period of 2 ka as a result of the interplay between fault segments to the south and north of the JGF.
The Northern end of the Dead Sea Basin: Geometry from reflection seismic evidence
Tectonophysics, 2007
Recently released reflection seismic lines from the Eastern side of the Jordan River north of the Dead Sea were interpreted by using borehole data and incorporated with the previously published seismic lines of the eastern side of the Jordan River. For the first time, the lines from the eastern side of the Jordan River were combined with the published reflection seismic lines from the western side of the Jordan River. In the complete cross sections, the inner deep basin is strongly asymmetric toward the Jericho Fault supporting the interpretation of this segment of the fault as the long-lived and presently active part of the Dead Sea Transform. There is no indication for a shift of the depocenter toward a hypothetical eastern major fault with time, as recently suggested. Rather, the north-eastern margin of the deep basin takes the form of a large flexure, modestly faulted. In the N-S-section along its depocenter, the floor of the basin at its northern end appears to deepen continuously by roughly 0.5 km over 10 km distance, without evidence of a transverse fault. The asymmetric and gently-dipping shape of the basin can be explained by models in which the basin is located outside the area of overlap between en-echelon strike-slip faults.
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.
Historical seismicity of the Jordan Dead Sea Transform region and seismotectonic implications
Arabian Journal of Geosciences, 2014
Based on all available files, catalogs, and previous compilations, it is found that 96 historical earthquakes (M≥6.0) were felt along the Jordan Dead Sea Transform region during the last 2,000 years. More than 50 % of these occurred in the form of sequences and swarms that lasted for different periods, some of which were volcanic related. The largest assigned magnitude is 7.6 with 667 years recurrence period, while the maximum possible future magnitude is 7.8±0.2 with 1,000± 80 years recurrence period. Quiescent periods, with a duration of up to 200 and 400 years and characterized by reduced levels of seismicity, are punctuated by active periods of tens of years when a few large earthquakes occurred. The historical seismicity indicates that all tectonic elements of the study region are presently active. Our results indicate that previous studies overestimate the level of seismicity in this region. Not less than 25 earthquakes, most of which had M≥7.0, are erroneously related to the transform. It is probable that most of these are located within the East Mediterranean region and/or along intraplate faults, rather than the Jordan Dead Sea Transform. This is evidenced by (i) frequency-magnitude results, (ii) moderatelarge East Mediterranean tsunamis, (iii) an apparent higher seismicity of the northernmost three segments compared with the southern three, (iv) relatively high annual seismic slip rate as calculated from the compiled historical seismicity, and (v) overdependence of some previous compilations on secondary rather than primary sources. The revised historical seismicity implies an annual seismic slip rate of about 0.68 cm/year, which indicates that not less than 30 % of the tectonic movements along the regional structures of the study region are aseismic. This is in agreement with results obtained from prehistoric and instrumental data.