dc.description.abstract | Using Microtremor Measurement To Study The Site Effect
In Taiwan Area
Jyun-yan Huang
Instisute of Geophysics, National Central University,
Chungli, Taiwan, R.O.C.
ABSTRACT
In this study, the high density microtremor surveys are done in whole Taiwan
except the mountain area. The studying regions include Taipei basin, Taoyuan,
Hsinchu and Miaoli, Taichung basin, Chianan Plain, Kaohsiung, Pintung,
Hualien, Taidong and Yilan plain. The main idea of this study is to
integrate the different area’s results which finished by predecessors, and use the same
standard to process data again, in order to study the site effect in whole
Taiwan.
The two-station spectral ratio method was used to figure out the local site effect
previously. But now, in this study, we use the H/V spectral ratio method
(Nakamura, 1989) to do the research. If we used the two-station spectral method, the
referent rock site station will be difficult to find, so we choose the H/V spectral ratio
method because it can figure out the site effect only by using a single station.
The dominant frequency and amplification ratio of each survey point were
calculated, and reduced it into site conditions, such as thickness of the deposition and
the S-wave velocity. The equivalent contours of the dominant frequency and the H/V
ratio in different frequency bands were plotted. The dominant frequency shows that
the station with thin deposition like rock site, show the higher dominant frequency.
On the other hand, the station with thick deposition, it goes low. The dominant
frequency also response the S-wave velocity, in which station the S-wave velocity
become lower, the dominant frequency become lower too.
Traditionally, estimating the potential of liquefaction takes time and the
processes are multifarious. Nakamura(1996) found the relationship between potential
of liquefaction and the factors in the H/V spectral method, includes dominant
frequency and amplitude ratio. That we can calculate the potential of liquefaction
quickly now and compared the results with NCREE’s results in this study.
Final, the results are combined with the GIS system to spread out. And hope
these results can be used in many purposes like earthquake engineering, disaster
prevention and cure, seismic analysis and design of structure.
(Key words:site effect、microtremor、spectral ratio、Taiwan)
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