Blackwell Publishing Journal Backfiles 1879-2005
Small earthquakes in the Dead Sea depression, part of the Jordan valley-Dead Sea rift, were recorded and analysed. With 117 identified events of 0.5 ≤ML≤ 4.2, the microseismicity, recorded by a local portable network during a period of about 20 months, shows a normal rate of seismicity for the region with b values around 0.8. The recorded seismicity is mainly confined to the basin and its boundaries. In the southern part of the Dead Sea basin we found a tendency to clustering, which is clearly demonstrated in very similar seismograms of several events recorded at the same station. Two clusters on the eastern fault are separated by an area with no seismicity for at least 5 yr. Relative location of events in one of the clusters exhibits a clear north-south lineament. Two active north-south left-lateral strike-slip faults along the east and west boundaries of the southern section of the Dead Sea basin are distinguished and confirmed by using composite focal mechanism solutions. In four, out of more than 60 events, we found normal faulting, where one has a ML= 4.1. For 34 events with 1.6 ≤ML≤ 4.2 we found seismic moment estimates, M0, of 1.2 × 1019≤M0≤ 2.3 times 1022 dyne cm and Brune stress drop estimates, Δs̀, between 0.6 and 92 bars. For earthquakes of M0 smaller than about 5 times 1021 dyne cm, we found only small variations in corner frequency, f0, resulting in decreasing Δs̀ with decreasing M0. This breakdown of the scaling relation for small earthquakes suggests an fmax slightly lower than 10 Hz for the Dead Sea region. The fmax is confirmed by available accelerometer data.
Type of Medium: