In recent years, there has been a great deal of interest to assess the
local site response, which is one of the key components of any seismic
risk analysis. The empirical method is one of the several techniques to
compute the spectral ratios of horizontal and vertical components (H/V)
using microtremor records, a method proposed by Nakamura (1989). Recent
studies of large destructive earthquakes have shown that damage during
the earthquakes are often caused by the amplification of seismic waves
in near-surface sedimentary layers. Studies of historical earthquakes
for the past few thousand years demonstrate that the damaging
earthquakes in Palestine were located along the Dead Sea Transform (DST)
fault. In the past century, a destructive earthquake has occurred in
the Jordan rift region at the boundary between the Arabian and the
Sinai–Palestine plates: Nablus earthquake of 11 July 1927 north Jericho
(M 6.2). The most recent earthquake of 11 February 2004 (Mb 5.1) also in
the Dead Sea Region (about 16 km south of Jericho city with a focal
depth of 21 km) caused some partially damage cases; in Nablus city few
historical buildings have been affected with damages between grade 2 to
grade 4 according to EMS-98. A study on the H/V ratio of microtremor
motion at the rock substratum is presented using records from
3-component digital seismograph installed in two Palestinian cities:
Nablus and Ramallah. Spectral ratios were computed for different
sedimentary sites, where the youngest sediments of Quaternary alluvium
and alternating layers of unconsolidated sedimentary materials give the
highest amplification factors. Our results show a good correlation
between the site amplification and the damage areas of Nablus earthquake
of 11 July, 1927 and the disastrous effects of the recent earthquake of
11 February 2004.
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