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TitleAn assessment of uncertainties in Vs profiles obtained from microtremor observations in the phased 2018 COSMOS blind trials
AuthorAsten, M W; Yong, A; Foti, S; Hayashi, K; Martin, A J; Stephenson, W J; Cassidy, J FORCID logo; Coleman, J; Nigbor, R L; Castellaro, S; Chimoto, K; Cho, I; Cornou, C; Hayashida, T; Hobiger, M; Kuo, C-H; Macau, A; Mercerat, E D; Molnar, S; Pananont, P; Pilz, M; Poovarodom, N; Saez, E; Wathelet, M; Yamanaka, H; Yokoi, T; Zhao, D
SourceJournal of Seismology 2022 p. 1-24, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20200665
Mediapaper; on-line; digital
File formatpdf
SubjectsHealth and Safety; tectonics; seismicity; seismology; seismic arrays; earthquake damage; earthquakes; earthquake risk; earthquake studies; seismic velocities
Illustrationstables; graphs; seismic velocity profiles; plots
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2022 01 01
AbstractSite response is a critical consideration when assessing earthquake hazards. Site characterization is key to understanding site effects as influenced by seismic site conditions of the local geology. Thus, a number of geophysical site characterization methods were developed to meet the demand for accurate and cost-effective results. As a consequence, a number of studies have been administered periodically as blind trials to evaluate the state-of-practice on-site characterization. We present results from the Consortium of Organizations for Strong Motion Observation Systems (COSMOS) blind trials, which used data recorded from surface-based microtremor array methods (MAM) at four sites where geomorphic conditions vary from deep alluvial basins to an alpine valley. Thirty-four invited analysts participated. Data were incrementally released to 17 available analysts who participated in all four phases: (1) two-station arrays, (2) sparse triangular arrays, (3) complex nested triangular or circular arrays,and (4) all available geological control site information including drill hole data. Another set of 17 analysts provided results from two sites and two phases only. Although data from one site consisted of recordings from three-component sensors, the other three sites consisted of data recorded only by vertical-component sensors. The sites cover a range of noise source distributions, ranging from one site with a highly directional microtremor wave field to others with omni-directional (azimuthally distributed) wave fields. We review results from different processing techniques (e.g., beamforming, spatial autocorrelation, cross-correlation, or seismic interferometry) applied by the analysts and compare the effectiveness between the differing wave field distributions. We define the M index as a quality index based on estimates of the time-averaged shearwave velocity of the upper 10 (VS10), 30 (VS30), 100 (VS100), and 300 (VS300) meters and show its usefulness in quantitative comparisons of VS profiles from multiple analysts. Our findings are expected to aid in building an evidence-based consensus on preferred cost-effective arrays and processing methodology for future studies of seismic site effects.
Summary(Plain Language Summary, not published)
This paper reviews the "blind-test" results where many groups from around the world use common datasets (for a wide variety of geological settings) and common processing techniques to determine the shear-wave velocity at the test sites. We then compare the results from different groups to see if the results are similar, or what is common (or different), in an effort to determine best data collection and processing practises for determining earthquake site response. The results of the study will aid in building an evidence-based consensus on preferred cost-effective arrays and processing methodology for future site-effect studies for direct application to earthquake hazard studies.

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