Seismological observations of the northern Dead Sea basin earthquake on 11 February 2004 and its associated activity

We present seismological observations and analysis of the northern Dead Sea basin earthquake, M_w 5.1, on 11 February 2004. The mainshock was followed by a relatively short sequence of aftershocks. These lasted for about 4 weeks (most occurring in the first few days) and were of small magnitude. Most of the aftershocks occurred west of the mainshock, along a transverse line crossing the northern Dead Sea basin from ESE to WNW. The focal plane solution of the mainshock suggests a strike-slip faulting. The focal mechanisms of the aftershocks present mainly strike-slip motion but also some normal and reverse faulting. A clear directivity effect for the mainshock was revealed in records of accelerometers and broadband seismic stations for an azimuth corresponding to the main strike determination. Measured amplitude values fit well the theoretical directivity factor obtained by a new stochastic superposition model based on unilateral rupture propagation, random character of stress energy release, rupture velocity, and slip amplitude. For 81 earthquakes in the coda magnitude range of 1.1 ≤ M_d ≤ 5.2 we found seismic moment estimates with values ranging from 1.02 × 10¹¹ N-m to 3.78 × 10¹⁶ N-m, and Brune stress drop estimates, Δσ, between 1 and 40 bars. These characteristics are comparable to those for earthquakes occurring on the main Dead Sea-Jordan fault.