Coda Q in southwestern British Columbia, Canada

Coda decay rates of 122 locally recorded earthquakes are used to infer freq uency-dependent coda Q values at 21 short-period stations in southwestern B ritish Columbia, Canada. Using the single-scattering model, coda Q values ( Q(c)) are derived for a range of sampling volumes corresponding to maximum lapse times of 36-59 sec and maximum sampling depths of 70-110 km. Maps of Q(0) (Q(c) inferred at 1 Hz) for different sampling volumes show a consiste nt trend of increasing Q(0) to the northeast away from the subduction zone and into the Coast Belt batholith, and decreasing Q(0) toward the southeast ern-most stations near the Vedder fault at the southern terminus of the Coa st Belt. Q(0) increases gradually with sampling volume at all stations. The dependence of Q(c) on frequencies between 2 and 16 Hz for different statio ns varies but on average ranges from 280 at 2 Hz to 850 at 16 Hz for sampli ng volumes that extend to depths of similar to 90 km. An average of all dat a for the same sampling volume size gives a relationship of Q(c) = 110 f(0. 72) for frequencies in the 2- to 16-Hz range, which suggests significant di fferences in lithospheric coda attenuation properties in comparison with no rthwestern Washington State where Q(c) = 63 f(0.97). Changes in coda Q corr elate with the volume of brittle and fractured continental and subducting o ceanic lithosphere sampled.