Microzoning of site response parameters in the towns of Dimona and Bet Shean (Israel)

Due to their proximity to the seismically active Dead Sea Fault system, the towns of Dimona and Bet Shean are considered high seismic risk zones. An investigation of the possible site amplification effects, using ambient noise surveys, was carried out at 275 sites in Dimona and 210 sites in Bet Shean. The soil sites exhibit H/V peak amplitudes ranging from 2 to 7 in the frequency range 1.0 Hz to 10 Hz. While integrating data from the extensive ambient noise measurements, information about the regional geology and S-wave velocity profiles derived from a few refraction lines enabled the construction of multi-layer soil-column models that yield analytical site response functions which are consistent with the observed H/V spectral ratios. We divided the study areas into zones and characterized each of them with a generalized soil column model. Thus the seismic hazard zonation maps obtained are closely tied to site effects actually measured, and therefore may lead to realistic site-specific seismic hazard assessments in these towns, in spite of the paucity of borehole, refraction data and other subsurface information.