| dc.description.abstract | The influence of site effects can be an important factor in seismic triggering of landslides on unstable slopes. However, dynamic responses of unstable slopes to seismic shaking are poorly understood, because the scarcity of relevant seismometric data and its evaluation is made difficult by the complexity of the phenomena involved, link to surface geometry, local geology, amplified wave propagation, etc. The analysis presented by Del Gaudio and Wasowski (2007) show that slope response to seismic shaking can be characterized by directional variations with maxima amplification oriented along local topography features. The site amplification and directivity appears has occasionally been detected with maximum slope direction. This work attempt to explore the phenomenon based on microtremor measurement, and the test were performed at Bishan, Jiufengershan and Tasoling in Taiwan. At Bishan, all measurements are located on the same stratum, it points out that the amplification of these sites are influenced by topography and the value of HVNR of these sites near ridge can be 4-5. Further, we observed the response directivity at 1-3Hz are coincided with local topography. Summarize all directivity measured at dip-slope faces, most results are with dip direction and some exceptions are linked to the local site features. It shows that microtremor is easily affected by local geology and topography conditions. A comparison of microtremor results with records of an accelerometer CHY080 station at Tasoling shows that the microtremor and the strong motions have the same dominant frequency (1-3Hz). The directivity of the earthquakes which are met the criteria for site response directivity identification presence the same amplification oriented with microtremor. However, the maximum amplification direction of Chi-Chi earthquake event provides a different of 70 degrees from microtremor results. It might due to the nature different between microtremor and seismic, the former is more related to local structures and the latter combines source properties and site effect. Considering the non-linearity of site response, it would need more investigation with moderate-strong earthquake data recorded at those unstable slopes to understand dynamic responses.
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