Ground motion amplification atop the complex sedimentary basin of Haifa Bay (Israel)

Abstract

The Zevulun Valley (ZV) is a sedimentary basin underlying the heavily populated and industrialized petrochemical hub of Haifa Bay, Israel. With active tectonic faults at close range and a mixture of large population and vulnerable facilities, the seismic risk in the ZV is high. However, until now the national seismic network in Israel only included rock stations with no measurements supporting the expected difference between the ZV and its surroundings. Moreover, a detailed analysis of ground motions atop sedimentary basins using earthquakes data was never conducted in Israel for any basin. In this paper, we present a dataset collected during a 16 months monitoring campaign with a transportable network deployed in the ZV. For the first time in Israel we simultaneously recorded earthquake (3.1 < Mw < 5.5) ground motions at basin- and reference-sites. Spectral ratios reveal amplification factors tangibly higher than those previously reported by horizontal-to-vertical-spectral-ratio (HVSR) techniques and 2-D modeling. In particular, the deeper parts of the valley exhibit ground motion amplification up to a factor of 8 at frequencies lower than 1 Hz. Comparison of the measured spectral ratios with the results of 1-D linear-elastic analysis shows partial correlation reflecting the complexity of the sub-surface structure.