MAGNITUDE mN RESIDUALS OF SOUTHERN ONTARIO – SOUTHWESTERN QUEBEC SEISMIC STATIONS

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

After 2000, seismic events in southern Ontario - western Quebec are recorded by a virtual seismograph network (Combined Southern Ontario - Southwestern Quebec Seismic Network (CSOWQSN)). In 2000-2005 this network comprised 51 stations in southern Canada, including 31 broadband stations of the Southern Ontario - Western Quebec POLARIS Network, 4 short-period dial-up stations of the University of Western Ontario and 16 stations from the Canadian National Seismic Network (CNSN). The CSOWQSN covers an area about 800 x 550 km with seismic stations installed in different site conditions. The main purpose of this study is to estimate the station magnitude residuals for all stations of CSOWQSN and reveal the influence of the local and regional factors on them. The magnitude residuals are calculated for all 51 stations of the CSOSQSN for the mN (Nuttli magnitude) as it is used in the practice of Geological Survey of Canada. Calculations are based on data from 1816 local and regional seismic events in the range mN 0.5 - 5.5 (889 earthquakes, 774 quarry blasts and 153 mining events) recorded from January 2001 to June 2005 by Geological Survey of Canada. The mean magnitude residuals vary between -0.29 and +0.97 mu and show a relation with the tectonic provinces where the stations are installed and the local site conditions. An attempt is made to separate the local and regional portion of the magnitude residuals for stations with over 100 observations. The theoretical site responses for a few stations installed on overburden are calculated using the available velocity models below the stations, and are compared with the observed magnitude residuals. Our results give a basis for more accurate magnitude estimations for local and regional events in southern Ontario - western Quebec.