Earthquake deformations in the Lisan deposits and seismotectonic implications

Abstract

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 décollement 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 décollement 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 ∓ 20yr for earthquakes with magnitudes greater than or equal to 6.5. Earthquakes with magnitude greater than 7 seem to have occurred along 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-1.