Site amplification at five locations in San Francisco, California: A comparison of S waves, codas, and microtremors

Linda C. Seekins; Leif Wennerberg; L. Margheriti; Hsi-Ping Liu

doi:10.1785/bssa0860030627

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Site amplification at five locations in San Francisco, California: A comparison of S waves, codas, and microtremors

Linda C. Seekins·Leif Wennerberg·L. Margheriti·Hsi-Ping Liu

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Abstract

We compare microtremor data to weak-motion S -wave and coda recordings at sites in San Francisco in order to clarify the range of applicability of microtremor data to ground-motion prediction. We also compare S -wave results to coda results. For each type of data, we compute spectral ratios of motions from two soil/rock station pairs and from an uphole/downhole pair in the Marina district. We compute horizontal/vertical ratios (Nakamura's method) at a soil site, a rock site, and the surface and borehole instruments. In the station-pair analyses, microtremor data show amplifications at the same fundamental frequency as S waves, but the frequencies of other peaks do not agree. The amplification at frequencies higher than 2 Hz is greater in the microtremor data. Station-pair ratios of coda data generally show spectral peaks occurring at the same frequencies, but with levels varying from one to four times the amplification from S -wave ratios. Nakamura's method of analyzing microtremors agrees better with S -wave station-pair results than the microtremor station-pair method over a limited frequency band that varies from station to station.

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Bulletin of the Seismological Society of America Article

Source-reported bounding extent: 37.25536096035685° to 38.33187057007001° latitude; -123.02509908452166° to -121.53093127807247° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Linda C. Seekins, Leif Wennerberg, L. Margheriti, Hsi-Ping Liu. 1996-06-01. Site amplification at five locations in San Francisco, California: A comparison of S waves, codas, and microtremors. https://doi.org/10.1785/bssa0860030627

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