CRUSTAL STRUCTURE AND SEISMICITY CHARACTERISTICS OF THE MANIWAKI CLUSTER, WESTERN QUEBEC

EATON, D.W., and DINEVA, S., Department of Earth Sciences, University of Western Ontario, London, Ontario, N6A 5B7, Canada, deaton@uwo.ca.

The seismicity in eastern North America exhibits strong spatial-clustering characteristics. Individual earthquake clusters provide the opportunity to observe and characterize earthquakes at rates of activity that are orders of magnitude higher than regional background seismicity, and could shed new light on the nature of intraplate seismicity. The Maniwaki cluster is one such small (20km x 15km x 11km) concentration of earthquake activity. It is located at ~ 47N 76.3W in the northern corner of the western Quebec seismic zone, in close proximity to the 434 square km Reservoir Cabonga and a crustal seismic profile acquired in 1993 as part of the Canadian Lithoprobe program. The Cabonga dam was built in 1928, so it is unlikely that the seismicity is directly related to flooding of the reservoir. Using regional depth phases, we have obtained focal depths of 15 - 26 km for 23 events in the magnitude range of 2.0 < M < 4.5. By fixing these independently derived focal depths, we have obtained more precise hypocenters. These have been projected along strike onto the deep seismic profile, allowing us to associate the earthquake activity with specific Precambrian structures. Careful analysis of the waveforms shows that while some earthquakes show repeating characteristics, other earthquakes show evidence for temporal changes in focal mechanism.