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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