Site Response from Ambient Vibrations in the Towns of Lod and Ramle (Israel) and Earthquake Hazard Assessment |
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| Authors: | Email author" target="_blank">Y?ZaslavskyEmail author A?Shapira M?Gorstein M?Kalmanovich V?Giller N?Perelman I?Livshits D?Giller I?Dan |
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| Institution: | (1) Seismology Division, Geophysical Institute of Israel, P.O. Box 182, Lod, Israel |
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| Abstract: | Throughout their long history, the towns of Lod and Ramle have been severely affected by strong earthquakes. The last destructive
earthquake occurred on July 11, 1927 and caused the destruction of large parts of these cities, reaching a seismic intensity
of VIII–IX on the MSK scale. Such a high intensity from a relatively distant earthquake (about 70 km) of magnitude 6.2 is
likely to be the result of local site effects of the sedimentary layers that may have significantly enhanced earthquake ground
motions.
This study is focused on estimating the seismic hazard to Lod and Ramle by implementing a three-step process (1) detailed
mapping of the characteristics of the H/V spectral ratios from ambient noise, (2) incorporating geological information and well data to construct subsurface models
for different sites within the investigated area and (3) estimating the seismic hazard in terms of uniform hazard site-specific
accelerations.
The horizontal-to-vertical spectral ratios of ambient noise were used to approximate the fundamental resonance frequencies
of the subsurface and their associated amplitudes. About 360 sites in Lod and Ramle were instrumented for varying periods.
The soil sites exhibits H/V peak amplitudes ranging from 4 to 6 in the frequency range 0.5–2.5 Hz. These data were used to constrain 1-D subsurface models
that were developed using geological data and borehole information. H/V spectral ratio observations were checked against theoretical subsurface transfer functions at locations where borehole information
is available farther constraint the range of possible Vs velocities of the different layers and thus, by means of trial an error it was possible to conclude a systematic spatial
distribution of the Vs velocity and thickness in the substrata that are also consistent with the spatial distribution of the fundamental resonance
frequencies of the soft sediments obtained by means of the H/V spectral ratios, and other geological and geophysical information available at different locations in the study area.
The evaluated subsurface models are introduced using the SEEH procedure of Shapira and van~Eck (1993) Natural Hazards 8, 201–205] to assess Uniform Hazard Site-Specific Acceleration Spectra for different zones within the towns of Lod and Ramle.
These evaluations are very important for realistic assessment of the vulnerabilities of all types of existing and newly designed
structures and for urban and land use planning. |
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| Keywords: | acceleration spectra ambient vibrations hazard assessment microzonation site amplification site response spectral ratio |
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