The site effect and the possibility of trap wave in the Longitudinal valley of eastern Taiwan

Speaker: Kuei-Mei Lin

Abstract

Taiwan is located along the plate boundary between the Eurasian Plate and the Philippine Sea Plate. Collision between the two plates takes place along the Longitudinal valley (LV) with a highly convergence rate of 82 mm/yr. The Longitudinal valley is considered as the collision suture between the two plates. There are numerous earthquakes and many active faults here, and the underground active tectonics is very complicated. Its tectonic implications and seismicity have long been a primary research focus in the central eastern Taiwan.

The two-station spectral ratio method was used to figure out the local site effect previously. In this study, we use the H/V spectral ratio method (Nakamura, 1989) to do the research. The referent rock site station will be difficult to find when we used the two-station spectral method, so we choose the H/V spectral ratio method because it can figure out the site effect only by using a single station.

Li (2004) reported that a fracture zone may form a low-velocity zone and trap some waves inside the fault. From the regional geology setting, we want to know if the Longitudinal valley can trap waves just like a low-velocity zone. In this study, the trapped waves were identified from the observed seismograms based on the characteristics list (Li et al. 1998, Ben-Zion 1998) and the amplitude and particle motion were also analyzed.

References

•  Li, Y. G., John E. Vidale and Elizabeth S. Cochran (2004) Low-velocity damaged structure of the San Andreas Fault at Parkfield form fault zone trapped waves. Geophysical Research Letters, 31, L12S06

•  Li, Y. G., Chen, P., Cochran, E. S., Vidale, J. E., and Burdette, T., (2006). Seismic evidence for rock damage and healing on the San Andreas Fault associated with the 2004 M6.0 Parkfield earthquake, Bull. Seism. Soc. Am., 96, 349-363