| Title | A preliminary assessment of uncertainties attributed by analysts, array types and processing algorithms for microtremor observations, via the COSMOS blind trials |
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| Author | Asten, M W; Yong, A; Foti, S; Hayashi, K; Martin, A; Stephenson, W J; Cassidy, J F ; Coleman, J |
| Source | AEGC 2019: Australasian Exploration Geoscience Conference, Perth, Australia, program; 184, 2019 p. 1-4  Open Access |
| Links | Online - En ligne (PDF, 315 KB)
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| Image |  |
| Year | 2019 |
| Alt Series | Natural Resources Canada, Contribution Series 20190273 |
| Meeting | AEGC 2019: Australasian Exploration Geoscience Conference; Perth; AU; September 2-5, 2019 |
| Document | Web site |
| Lang. | English |
| Media | digital; on-line |
| File format | pdf (Adobe® Reader®) |
| Subjects | geophysics; 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 |
| Illustrations | profiles; plots |
| Program | Public Safety Geoscience Assessing Earthquake Geohazards |
| Released | 2019 09 01 |
| Abstract | (Summary)
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. |
| GEOSCAN ID | 315014 |
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