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Coda Q in the Charlevoix, Quebec, region: Lapse-time dependence and spatial and temporal comparisons

Geological Survey of Canada Geophysics Division, Ottawa, Ontario, Canada , K1A 0Y3

Abstract

Coda Q is determined in the seismically active Charlevoix region, Quebec, using 34 earthquakes recorded on the six-station Charlevoix Local Telemetered Network. For comparison, an average value of coda Q for southeastern Canada is determined from 32 events that occur over a much larger region. At lapse times of 20 to 40 sec, coda Q at 1 Hz (Q₀) at Charlevoix and for southeastern Canada is 91 ± 4 and 125 ± 10, respectively. At a 40 to 80 sec lapse time, it is 200 ± 3 and 305 ± 15, respectively. The lower Q₀ value at Charlevoix in comparison with other parts of southeastern Canada is in agreement with Jin and Aki's (1988) finding that Q₀ is lower in the vicinity of large earthquakes.

No statistically significant temporal change in coda Q at Charlevoix is observed over the 11 yr of data studied. A variation of as little as 15% would be statistically apparent. Ongoing monitoring of coda Q in the area is planned using the local network in order to investigate any temporal changes prior to future large earthquakes.

Coda Q is found to increase with lapse time. (Lapse time is defined as time elapsed after the origin time.) This dependence could be due to any of the following: Nonzero source-receiver distance; nonisotropic scattering; scattering from below the crust; multiple scattering; or increase of Q with depth or with distance from both source and receiver.

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				B. C. Zelt, N. T. Dotzev, R. M. Ellis, and G. C. Rogers Coda Q in southwestern British Columbia, Canada Bulletin of the Seismological Society of America, August 1, 1999; 89(4): 1083 - 1093. [Abstract] [PDF]

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