Abstract
Rockbursts are a major hazard in the Coeur d'Alene mining district of northern Idaho. To study the source mechanisms of mining‐related seismicity, we operated 15 portable seismographs in the Coeur d'Alene mining district for one week in September 1990. We found the velocity model of the district to consist of a halfspace with a P wave velocity of 5.74 km/s and an S wave velocity of 3.47 km/s. In‐mine seismic monitoring systems provided excellent control on the velocity model and most hypocenter locations. Twenty‐one events, with sufficient focal sphere coverage for fault plane solutions, were recorded. Eleven of the events produced all‐dilatational first motions; for all events, 90% of first motions observed were dilatational. Ten events produced unsolvable first‐motion data in terms of the usual double‐couple mechanism, but seven of these unsolvable events were found consistent with an implosional source and two others were consistent with a shear‐implosional source. Our results provide firm observational evidence that dilatational first motions are predominant in this deep metal‐mining district, probably the result of implosional and shear‐implosional source mechanisms.
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