Abstract

The Dead Sea Transform (DST) dominates the seismicity of Israel and neighboring countries. Whereas, the instrumental catalog of Israel (1986 - 2017) contains mainly M < 5 events, the pre-instrumental catalog lists fourteen M 7 or stronger events on the DST during the past two millennia. GPS measurements show that the slip deficit in northern Israel today is equivalent to M > 7 earthquake. This situation highlights the possibility that a strong earthquake may strike north Israel in the near future, raising the importance of ground motion prediction.

Deep and narrow strike-slip basins accompany the DST. Here we study ground motions produced by intra-basin seismic sources in order to understand the basin-effect on regional ground motions. We model seismic wave propagation in 3-D, focusing on scenarios of Mw 6 earthquakes rupturing different active branches of the DST. The geological model includes the major structures in northern Israel: the strike-slip basins along the DST, the sedimentary basins accompanying the Carmel Fault Zone, and the densely populated and industrialized Zevulun Valley (Haifa Bay area).

We show that regional ground motions are determined by source-path coupling effects in the strike-slip basins before waves propagate into the surrounding areas. In particular, ground motions are determined by the location of the rupture nucleation within the basin, the near-rupture lithology, and the basin's local structure. When the rupture is located in the crystalline basement or along material bridges connecting opposite sides of the fault, ground motions behave predictably, decaying due to geometrical spreading and locally amplified atop sedimentary basins. By contrast, if rupture nucleates or propagates into shallow sedimentary units of the DST strike-slip basins, ground motions are amplified within before propagating outside. Repeated reflections from the basin walls result in a "resonant chamber" effect, leading to stronger regional ground motions with prolonged durations.