Ambient Seismic Noise Analyses in Western Foothills

Ambient Seismic Noise Analyses in Western Foothills

The Western Foothills geologic province is located along the deformation front of the Taiwan Orogen. This area includes highly active faults and a complex seismogenic structure that have historically caused serious damage. A temporary seismic network with around 40 broadband seismometers had been set up between Hsinchu and Tainan County and had been operated for about two years by the National Center for Research on Earthquake Engineering (NCREE) to monitor the seismicity surrounding the three Science Parks. Meanwhile, the characteristics of ground motion and fault activity could be further studied. The theorems for analyzing ambient seismic noise to investigate subsurface velocity structures have been proved and generally accepted. Data quality of daily vertical components was preliminarily assessed to calculate the cross-correlation function (CCF) for each station pair in the 1–15-s period band. The daily CCFs were stacked monthly and the monthly CCFs were then stacked to retain coherent signals for acquiring time-domain empirical Green's functions (TDEGFs) and Rayleigh-wave phasevelocity dispersion curves. Tomography was applied to construct Rayleigh-wave phase-velocity maps and shallow crustal S-wave velocity (Vs) structures were also obtained.