A 40,000 year unchanging seismic regime in the Dead Sea rift

Abstract

We studied breccia beds in lacustrine sediments within the active Dead Sea basin. The beds were deformed by M >5.5 earthquakes during the past 60 k.y. Our new analysis considers both the thickness of breccia beds and the lithology of beds directly overlying them in order to identify 11 M >7 earthquakes that originated within the Dead Sea pull-apart between 54 and 16 ka. The resulting time series is a unique long record of earthquakes in a well-constrained segment of a fault system in which the time interval between consecutive earthquakes increased from hundreds of years to a background recurrence interval of ∼11 k.y. since ca. 40 ka. Since this recurrence interval is similar to the M ≥7.2 recurrence interval in the Dead Sea basin, as extrapolated from present seismicity, we suggest that the present seismic regime in the Dead Sea basin, as reflected in its magnitude-frequency relation as well as in its deficiency in seismic moment, has been stationary for the past ∼40 k.y. Since the increasing interval between consecutive earthquakes in the studied segment of the Dead Sea fault is time-logarithmic, it may be a result of healing of the brittle crust as well as a diminishing strain rate following the first strong earthquake in the sequence.