The Difference in Site Response Characteristics Inferred between The Two Stations Pairs method and Nakamura's method.
Speaker: Hsuan-Jui Hsu
Abstract
The seismic acceleration waveforms at the same observation station are generally similar without too much variation between different earthquakes. Though there is a trend that a high-frequency when the small magnitude earthquake and the low-frequency when the large magnitude. Means the site response characteristics is important factor to earthquake disaster.
In general, to understand site response characteristics the two soil/rock station pairs and uphole/downhole pair methods were used. The two soil/rock stations pair method compares a soft-soil site to a nearby hard-rock reference site. But the hard-rock reference site was difficult to find in nearby soft-soil site. So the distance with soft-soil site and hard-rock reference site was a problem. The borehole stations pairs was very rare.
The Nakamura’s method (horizontal/vertical spectral ratio) could solve the problems that the two soil/rock stations pair and uphole/downhold pairs in Marina district. Because the Nakamura’s method just need single station. This studies employing several earthquake events that S-wave and coda wave date to analyzing the site effect. The H/V spectral ratio similar to soil/rock (uphole/downhole) stations pair in predominant frequency. And the H/V spectral ratio had more least standard deviation than soil/rock (uphole/downhole) stations pair by several earthquake events
Reference
Nakamura, Y. S A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface. QR of RTR1 1989, 30, 1.
Seekins, L.C., Wennerberg, L., Margheriti, L. & Liu, H.P. Site Amplification at Five Locations in San Francisco, California: A Comparison of S Waves, Codas, and Microtremors. Bulletin of the Seismological Society of America, 1996, 86, No. 3, 627-635