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Simulation of seismic wave propagation through geometrically complex basins - the Dead Sea basin

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The Dead Sea Transform (DST) is the source for some of the largest earthquakes in the Eastern Mediterranean, including the 1927 MW 6 .2 Jericho earthquake and the 1995 MW 7 .2 Gulf of Aqaba earthquake. The seismic hazard presented by the DST threatens the Israeli, Palestinian and Jordanian populations alike. Several deep and structurally complex sedimentary basins are associated with the DST . These basins are up to 10 km deep and typically bounded by active fault zones.

The low seismicity rate of the DST combined with a sparse seismic network in Israel that provides poor coverage of sedimentary basins, results in a critical knowledge gap. It is therefore necessary to complement the limited instrumental data with synthetic data based on computational modeling, in order to study the effects of earthquake ground motion in these sedimentary basins.

In this research we performed a ground motion analysis in the Dead Sea Basin (DSB) using a finite-difference code capable of simulating seismic wave propagation in a 3-D heterogeneous earth. Two 2-D cross-sections transecting the DSB were compiled based on currently available geological and geophysical data and were used for wave propagation simulations. Results indicate a complex pattern of ground motion amplification affected by the geometric features in the basin.

To distinguish between the individual contributions of each geometrical feature in the basin, we developed a semi-quantitative decomposition approach. This approach enabled us to interpret the DSB results as follows: (a) Ground motion amplification as a result of resonance and anelastic effects, occurs basin-wide due to a high impedance contrast at the base of the uppermost layer. (b) Steep faults generate a strong edge-effect that further amplifies ground motions. (c) Sub-basins cause geometrical focusing that under certain circumstances significantly amplifies ground motions. (d) Salt diapirs diverge seismic energy and cause a decrease in ground motion amplitude.

This talk is part of the Department of Earth Sciences Seminars (downtown) series.

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