Coda Q in the Northern Cascadia Subduction Zone
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| Authors: | Farahbod, AM; Calvert, AJ; Cassidy, JF; Brillon, C |
| Year: | 2016 |
| Journal: | Bull. Seismol. Soc. Amer. 106: 1939-1947 Article Link (DOI) |
| Title: | Coda Q in the Northern Cascadia Subduction Zone |
| Abstract: | Using seismograms recorded at 66 Canadian seismic stations, coda Q was estimated from earthquakes in southwestern British Columbia and northern Washington State, employing the single backscattering approximation. A total of 580 earthquakes with magnitudes ranging from 1.2 to 6.4, depths from 0 to 67 km, and epicentral distances of 5-110 km were selected to obtain 3022 high signal-to-noise ratio traces for analysis. An average of all the data yields a relationship for coda Q of Q(C) = 72 f(0.91). There is little variation of this coda Q relationship when using either crustal or in-slab sources, which represent uniform sampling of the crust and upper mantle. Crustal earthquakes result in a relationship of Q(C) = 73 f(0.89), and for in-slab events Q(C) can be expressed as Q(C) = 69 f(0.94). In general, Q(0) (Q(C) at 1 Hz) increases from the west coast of Vancouver Island to the east-southeast within the Coast belt. Stations on west-central Vancouver Island closest to the landward projection of the Nootka fault zone, and the location of the only two known large crustal earthquakes (1918 M similar to 7 and 1946 M similar to 7: 3) on Vancouver Island, have the lowest Q(0) values in our study area, suggesting a contrast in Q between the north and south of the island. |
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