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TitleMultichannel alignment of s-waves
AuthorBostock, M G; Plourde, A PORCID logo; Drolet, D; Littel, G
SourceBulletin of the Seismological Society of America vol. 112, no. 1, 2022 p. 133-142,
Alt SeriesNatural Resources Canada, Contribution Series 20210130
PublisherSeismological Society of America
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia
NTS92B/02; 92B/03; 92B/06; 92B/07; 92B/10; 92B/11
Lat/Long WENS-123.5000 -122.5000 48.7500 48.0000
Subjectstectonics; mathematical and computational geology; p waves; s waves; seismic waves; earthquakes
Illustrationsschematic diagrams; location maps; seismic profiles; seismic sections; plots
Released2021 09 14
AbstractHigh resolution earthquake locations and structural inversions using body waves rely on precise delay-time measurements. Subsample accuracy can be realized for P-waves using multichannel cross correlation (MCCC), as developed by VanDecar and Crosson (1990), that exploits redundancy in pair-wise cross-correlations to determine delays between similar waveforms in studies of mantle structure using teleseismic sources (common-source/multiple-stations) and regional studies of structure and seismicity (common-station/multiple sources). For regional S-waves, alignment is complicated by the additional degree of freedom in waveform polarity that is expressed for sources with different moment tensors. Here we recast MCCC within a principal component framework and demonstrate the equivalence between maximizing waveform correlation and minimization of various singular-value-based objective functions for P-waves. The singular-value framework is more general and leads naturally to an MCCC linear system for S-waves that possesses an order of magnitude greater redundancy than that for P-waves. Robust L1 solution of the system provides an effective means of mitigating outliers at the expense of subsample precision. Residual time shifts associated with higher-order singular vectors are employed in an iterative adaptive alignment that achieves subsample resolution. We demonstrate application of the approach on a seismicity cluster within the northern Cascadia crustal fore-arc.
Summary(Plain Language Summary, not published)
Precise estimates of earthquake locations help us understand both earthquake hazard and the geological structure of earth's crust. To achieve precise locations, we often assume that nearby earthquakes produce highly similar waveforms. However, while this is true for compressional (P) waves, it is not necessarily true for shear (S) waves. This paper presents a new method for processing S waves from groups of nearby earthquakes in order to estimate precise locations. The method is tested on a group of over 100 earthquakes from southwestern British Columbia.

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