Publication Date:
2016-07-26
Description:
Although the time-averaged shear-wave velocity down to 30 m depth ( V S 30 ) can be a proxy for estimating earthquake ground-motion amplification, significant controversy exists about its limitations when used as a single parameter for the prediction of amplification. To examine this question in absence of relevant strong-motion records, we use a range of different methods to measure the shear-wave velocity profiles and the resulting theoretical site amplification factors (AFs) for 30 sites in the Newcastle area, Australia, in a series of blind comparison studies. The multimethod approach used here combines past seismic cone penetrometer and spectral analysis of surface-wave data, with newly acquired horizontal-to-vertical spectral ratio, passive-source surface-wave spatial autocorrelation (SPAC), refraction microtremor (ReMi), and multichannel analysis of surface-wave data. The various measurement techniques predicted a range of different AFs. The SPAC and ReMi techniques have the smallest overall deviation from the median AF for the majority of sites. We show that V S 30 can be related to spectral response above a period T of 0.5 s but not necessarily with the maximum amplification according to the modeling done based on the measured shear-wave velocity profiles. Both V S 30 and AF values are influenced by the velocity ratio between bedrock and overlying sediments and the presence of surficial thin low-velocity layers (〈2 m thick and 〈150 m/s), but the velocity ratio is what mostly affects the AF. At 0.2〈 T 〈0.4 s, the AFs are largely controlled by the surficial geology of a particular site. AF maxima are the highest in the hard classes, which is the inverse of the findings used in the Australian Building Code. Only for T 〉0.5 s do the amplification curves consistently show higher values for soft site classes and lower for hard classes.
Print ISSN:
0037-1106
Electronic ISSN:
1943-3573
Topics:
Geosciences
,
Physics
Permalink
