Soft-sediment deformation within seismogenic slumps of the Dead Sea Basin (original) (raw)
Related papers
2011
Although it has been tacitly assumed since the seminal work of Jones in the 1930s that slump folds bear a systematic and meaningful relationship to the slope upon which they were presumably created, there has in reality been very little attempt to objectively verify this association via the collection of regional slump data in a relatively controlled setting. The potential to walk around the intact Dead Sea Basin at c. 425 m below mean sea level provides a perhaps unparalleled opportunity to undertake such verification via the direct examination of slump fold relationships. The collection of slump data in this well-constrained environment, where the seismogenic trigger for slumping is established via earthquake records, and the palaeogeographical controls are also recognizable and clearly link to the present bathymetry and landscape, thereby permits an evaluation of the use of slump folds as indicators of palaeoslope. The Late Pleistocene Lisan Formation cropping out to the west of ...
A large-scale radial pattern of seismogenic slumping towards the Dead Sea Basin
Journal of the Geological Society, 2012
Although it has been tacitly assumed since the seminal work of Jones in the 1930s that slump folds bear a systematic and meaningful relationship to the slope upon which they were presumably created, there has in reality been very little attempt to objectively verify this association via the collection of regional slump data in a relatively controlled setting. The potential to walk around the intact Dead Sea Basin at c. 425 m below mean sea level provides a perhaps unparalleled opportunity to undertake such verification via the direct examination of slump fold relationships. The collection of slump data in this well-constrained environment, where the seismogenic trigger for slumping is established via earthquake records, and the palaeogeographical controls are also recognizable and clearly link to the present bathymetry and landscape, thereby permits an evaluation of the use of slump folds as indicators of palaeoslope. The Late Pleistocene Lisan Formation cropping out to the west of the Dead Sea contains superb examples of slump folds that systematically face (>95%) and verge (>90%) towards the east. This study employs and evaluates five statistical techniques, including a new mean axial-planar dip (MAD) method, to analyse relationships between the orientation of slump folds and palaeoslopes. We recognize for the first time that the direction of slumping inferred from slump folds and thrusts varies systematically along the entire c. 100 km length of the western Dead Sea Basin. SE-directed slumping is preserved in the north, easterly directed slumping in the central portion and NE-directed slumping at the southern end of the Dead Sea. They are interpreted to form part of a large-scale and newly recognized radial slump system directed towards the depocentre of the precursor to the Dead Sea, and to be triggered by earthquakes associated with seismicity along the Dead Sea Fault.
Journal of Geophysical Research: Solid Earth, 2017
We have studied the history of earthquakes over the past 70 kyr by analyzing disturbed sedimentary layers around the margins of the Dead Sea. However, we know little about disturbances in the basin depocenter, where water depth is~300 m, and accessible only by drilling. In this study, we compare disturbances from the Dead Sea depocenter, with the contemporaneous earthquake record (~56-30 ka) that was recovered on the western margin of the lake. This comparison allows us to discern the characteristics of disturbance in the different subaqueous environments and identify the source and sedimentary process of mass transport deposits. Our observations indicate that (i) the long disturbance sequences in the Dead Sea depocenter are composed of in situ deformation, slump, and chaotic deposits; (ii) earthquake-triggered Kelvin-Helmholtz Instability is a plausible mechanism for the in situ deformation in the lake center; (iii) the slump is slope area sourced; (iv) the unit of chaotic deposits is lakeshore sourced; and (v) earthquake-triggered slope instability is a viable mechanism for the slump and chaotic deposits. We further suggest that long sequences of disturbance in seismically active lake depocenters can be used to infer earthquake clusters. Plain Language Summary In order to extend the Dead Sea Fault earthquake record to preinstrumental time, we need to understand the processes that create disturbance in the basin depocenter where water depth is hundreds of meters. Here we report two disturbed sequences (4-22 m thick) that were drilled in the Dead Sea depocenter. We propose a seismic trigger based on the temporal correlation with previously established earthquake records in the Dead Sea margin. Three basic types of disturbance are defined: in situ deformation, slump, and chaotic deposits (mud-supported gravel). Our observations indicate that (i) earthquake-triggered Kelvin-Helmholtz Instability is a plausible mechanism for the in situ deformation in the Dead Sea depocenter; (ii) slumps are sourced in the slope area; (iii) chaotic deposits (mud-supported gravel) originate nearshore; and (iv) earthquake-triggered slope instability creates slump and chaotic deposits. Our results have widespread implications for studies of sediment disturbance in seismically active lakes, and we further suggest that long sequences of disturbance in such seismically active depocenters can be used to infer patterns of earthquake temporal distributions.
Prehistoric Seismic Basin Effects in the Dead Sea Pull-apart
Site effect is the specific response to earthquakes that is characteristic of the attributes of a site. The two-and three-dimensional shape of sedimentary basins may constitute an important factor of site effects. In sediment-filled basins, in which a lens of soft sediments overlies rocks with higher seismic velocities, two-dimensional resonance patterns may prolong the duration of shaking, and induce a large amplification, much larger than the one predicted from the corresponding one-dimensional analysis. The main source of these phenomena is the development within the basins of surface waves, including the vertically and elliptically polarized Rayleigh waves, and horizontally polarized Love waves.
Holocene Earthquakes Inferred from a Fan-Delta Sequence in the Dead Sea Graben
Quaternary Research, 2000
The Holocene sequence of the fan-delta of Nahal Darga, in Israel, records deformation associated with earthquakes related to the Dead Sea Transform in general and to the Jericho Fault in particular. The fan-delta sequence is well exposed, and 20 radiocarbon ages help to date the earthquakes that are inferred from (a) displacement along faults, (b) liquefaction features associated with 11 separate sandy and silty layers, and (c) slumped allocthonous bodies of sediments located directly above one of the main splays of the Jericho Fault. On average, an earthquake larger than M 5.5 has occurred approximately every 600 years. This estimate is based on the earthquake record of the complete stratigraphic sequence, with erosional hiatuses omitted from the calculations. The most recently deformed layer is related to the 1927 Jericho (M L 6.2) earthquake. This layer provides a modern analog for the style of soft-sediment deformation associated with earthquakes in the late Pleistocene and Holocene silty sand beds of the fan-delta complexes of the Dead Sea and its predecessor, Lake Lisan.
Earthquake deformations in the Lisan deposits and seismotectonic implications
Geophysical Journal International, 1986
Earthquake deformations and induced sedimentary structures preserved in Quaternary sediments include faults, folds, fissures, slumps, sand boils and other effects of liquefaction. Such deformations and structures are well preserved in the Lisan deposits of the Dead Sea. Of most importance are the fold-type deformations known as dbcollement structures which are present all along the eastern side of the Lisan and seem to decrease gradually westwards to disappear in the middle of the Lisan. These may indicate that palaeoearthquakes originating along the Araba fault have triggered such structures due to shaking of elastoplastic unconsolidated sediments over gentle slopes dipping to the west. Preliminary results from studies on dCcollement structures preserved in a section representing some 1733 years of continuous deposition in the uppermost? Pleistocene, in the vicinity of Wadi Araba, indicate that: (1) seismic activity has fluctuated with time. Average recurrence period is about 340 7 20yr for earthquakes with magnitudes greater than or equal to 6.5. Earthquakes with magnitude greater than 7 seem to have occurred alcng the Araba fault. (2) Deduced earthquake magnitudes conform to the frequency-magnitude relationship: log N = 5.24-0.68M. (3) The deduced seismic slip rate along the Araba fault seems to be not less than 0.64 5 0.04 cm yr-l.
Holocene seismic and tectonic activity in the Dead Sea area
Tectonophysics, 1981
. Holocene seismic and tectonic activity in the Dead Sea area. In: R. Freund and Z. Garfunkel (Editors), The Dead Sea Rift. Tectonophysics, 80: 235-254. The Dead Sea is a large, active graben within the Dead Sea rift, which is bounded by two major strike-slip faults, the Jericho and the Arava faults. We investigated the young tectonic activity along the Jericho fault by excavating trenches, up to 3.5 m deep, across its trace. The trenches penetrate through Late Pleistocene and Holocene sediments. We found that a zone, up to 15 m wide, of disturbed sediments exists along the fault. These disturbed sediments provide evidence for two periods of intensive activity or more likely, for two major earthquakes, that occurred during the last 2000 years. The earthquakes are evident in small faults, vertical throw of a few layers, cracks, unconformities and wide fissures. We further documented evidence for recent sinistral shear along the Jericho fault in deformed sediments and damage to an 8th Century palace on a subsidiary fault. We suggest that the two earthquakes may be correlated with the 31 B.C. earthquake and the 748 A.D. earthquake, reported by the ancients. * Present address: Woodward-Clyde Consultants, Three Embarcadero Center, San Fransisco, Calif. 94111 (U.S.A.).