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.

We study the propagation of seismic waves, the resulting ground motions, and their amplification atop sedimentary structures underlying continental passive margins. We employ a set of generic models with increasing complexity within a framework of a 3D numerical scheme. The basic geological structure and velocity model were derived from the subsurface of the Israeli coastal plain where soft sediments form a wedge over the stiffer bedrock and fill subsurface canyons that incise deep into the bedrock. Ground motions were modeled for both seaside and landside seismic sources. We show that for a landside source, peak ground velocities (PGVs) atop a sedimentary wedge are amplified by a maximum factor of 2.6 and on average by a factor of 1.6, relative to a reference model. This amplification is mainly due to the ellipticity of Rayleigh waves in the soft sediment layer. Spatial distribution of amplification factors shows that sedimentary wedges do not exhibit a prominent edge effect. Atop sediment-filled canyons and landside source, PGV are amplified by a maximum factor of 3.3, relative to a reference model, along the exposed part of the canyon. The PGV amplification factor in the canyon relative to adjacent hard-rock site is up to 2.4. PGV amplification atop the sediment-filled canyons is mainly due to the geometrical focusing of SH waves. Based on our findings, we present a simplified ground-motion amplification map for the Israeli coastal plain.