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TitleA preliminary assessment of uncertainties attributed by analysts, array types and processing algorithms for microtremor observations, via the COSMOS blind trials
AuthorAsten, M W; Yong, A; Foti, S; Hayashi, K; Martin, A; Stephenson, W J; Cassidy, J FORCID logo; Coleman, J
SourceAEGC 2019: Australasian Exploration Geoscience Conference, Perth, Australia, program; 184, 2019 p. 1-4 Open Access logo Open Access
LinksOnline - En ligne (PDF, 315 KB)
Alt SeriesNatural Resources Canada, Contribution Series 20190273
MeetingAEGC 2019: Australasian Exploration Geoscience Conference; Perth; AU; September 2-5, 2019
DocumentWeb site
Mediadigital; on-line
File formatpdf (Adobe® Reader®)
Subjectsgeophysics; surficial geology/geomorphology; Science and Technology; seismology; array seismology; microearthquakes; strong motion seismology; seismic arrays; earthquakes; earthquake risk; seismic risk; overburden thickness; sediments; gravels; clays; sands; glacial deposits; software; Consortium of Organizations for Strong Motion Observation Systems (COSMOS); Methodology; Data processing; alluvial sediments
Illustrationsprofiles; plots
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2019 09 01
The blind-trial studies conducted for the 2006 3rd International Symposium on the Effects of Surface Geology (Grenoble, France) and the 2015 Inter-comparison of methods for site PArameter and veloCIty proFIle charaCterization (InterPACIFIC) Workshop (Turin, Italy) evaluated the utility of microtremor array methods for characterizing seismic site conditions. These studies used a multiplicity of arrays but left an open question as to whether (and under what) conditions might sparse (low-cost) arrays be technically sufficient for the task. Similar questions arise when designing arrays for use in mapping cover thickness or buried high-velocity layers in mineral exploration.
In this study, the Consortium of Organizations for Strong Motion Observation Systems (COSMOS) blind trials used microtremor array data from four sites with geology ranging from deep alluvial valleys to an alpine valley. Data were incrementally released to approximately a dozen analysts in four phases: (1) 2-station linear arrays; (2) sparse triangular arrays; (3) complex nested triangular or circular arrays; (4) all available geological control including drill-hole data. While data from one site consisted of recordings from 3-component sensors, the other three sites consisted of data from vertical-component sensors only. The sites covered a range of noise source distributions, ranging from one site with a highly directional microtremor wave field, to others with distributed or omni-directional wave fields.
Here, we review the results based on the different processing algorithms (e.g., beam-forming, spatial autocorrelation, seismic interferometry) as applied by the analysts to the incrementally released data, and then compare the effectiveness between the differing wave-field distributions. The results of the study will aid in building an evidence-based consensus on preferred cost-effective arrays and processing methodology for future studies of earthquake hazard site-effects and cover thickness studies in mineral exploration.
Summary(Plain Language Summary, not published)
This invited 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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