S-Wave Velocity Structure of the Taichung Basin, Taiwan, Estimated from Array and Single-Station Records of Microtremors

Abstract

The objective of this study is to estimate the S-wave velocity structure of the Taichung basin in a near-fault region, which is needed for strong-motion evaluation for the 1999 Chi-Chi earthquake. We have conducted array measurements of microtremors with a total of 12 arrays at four sites and single-station measurements of microtremors at 48 sites in and around the Taichung basin. Based on the Rayleighwave inversion technique using phase velocities estimated from array records of microtremors, we find that a thick layer (the thickness of about 1000 to 1400 m) with an S-wave velocity of V S 1100 m/sec exists in the east-central part of the Taichung basin. We estimate the thicknesses of sedimentary layers above the preTertiary bedrock at 48 sites to fit calculated peak and trough frequencies of horizontal-to-vertical spectral ratios of Rayleigh waves to observed peak and trough frequencies, assuming the same S-wave velocities estimated using array records. The pre-Tertiary bedrock depth was estimated to be about 5 to 6 km in this region. The estimated thickness of the layer with V S ‫ס‬ 1100 m/sec is largest in the east-central part of the basin and rapidly decreases to less than 400 m in the northeastern and western parts inside the basin. The estimated S-wave velocity structures reasonably explain arrival time of initial P and S waves of aftershock records observed by Higashi et al. (2001).

Three‐dimensional VS profiling using microtremors in Kushiro, Japan

“…Several studies, e.g. [11][12][13][14] have also made a similar suggestion. The objective of this article is to explore the possibility of three-dimensional V S profiling using microtremors based on the field investigation conducted in the city of Kushiro, Japan.…”

Simulating Shallow Soil Response Using Wave Propagation Numerical Modelling in the Western Plain of Taiwan

“…The microtremor array technique is an effective tool that has been widely used to obtain the shear wave velocity structures in several areas in Taiwan (Satoh et al 2001;Huang and Wu 2006;Kuo et al 2009;Lin et al 2009;Wu and Huang 2013). However, the non-uniform distribution of survey sites in the literature makes mapping the shallow velocity structures to these depths laborious and unsatisfactory.…”

Apparent velocity estimation with P-SV ratio method

“…The travel time analysis is an intuitive way (Kosuke and Ping, 2005), Where the times of the fi rst onset or any other distinguishable part of the same phase for all instruments in an array are carefully selected. According to the times and the distances between the stations, the apparent velocity can be estimated (Satoh et al, 2001). This method requires interactive work.…”