Nonlinearity, liquefaction, and velocity variation of soft soil layers in Taiwan and Japan
Speaker: Hsuan-Jui Hsu
Abstract
We have been known that seismic waves generated by earthquakes are magnified by soft layers. The recent demonstrations of this effect were the 1985 Michoacan (Mexico) Earthquake ,1989 Loma Prieta (California) and 2002 331Earthquake Taipei(Taiwan). So estimating ground motion properties was very important.
Analyzing surface and borehole acceleration data that from the SMART1, LSST and SMART2 arrays in Taiwan and the Port Island in Japan. The data from SMART1, LSST and SMART2 arrays included strong motion (larger than 100 m/s2) and weak motion ( loss than 80 m/s2). The Port Island array’s data from the Hyogo-ken Nanbu Earthquake’s foreshocks, mainshock and aftershocks.
Data analysis used spectral ratio technique. The nonlinear site effects occurred the different peak frequencies and de-amplification during strong motion compared with those during weak motion. In the Port Island data, the liquefaction occurred the spectral ratio between surface and different depth could find a large variation. Using a genetic algorithm to forward the S-wave velocities structure before , during and after the mainshock that could understand the variation.
Reference
Aguirre, J. & Irikura, K. Nonlinearity, Liquefaction, and Velocity Variation of Soft Soil Layers in Port Island, Kobe, during the Hyogo-ken Nanbu Earthquake. Bulletin of the Seismological Society of America, 1997, 87, No. 5, 1244-1258.
Beresnev, I.A.?Wen, K.-L. &Yeh, Y.-T. Seismological evidence for nonlinear elastic ground behavior during large earthquakes. Soil Dynamics and Earthquake Engineering 1995, 14, 103-114.