NOISE CHARACTERISTICS OF THE COMBINED SOUTHERN ONTARIO SEISMIC NETWORK: LOCAL AND REGIONAL EVENT DETECTABILITY

MIHAYLOV, D., Department of Civil and Environmental Engineering, The University of Western Ontario, London, Ontario, Canada, N6A 5B9, DINEVA, S., and EATON, D., Department of Earth Sciences, The University of Western Ontario, London, Ontario, Canada, N6A 5B7, sdineva@uwo.ca, deaton@uwo.ca, dmihaylo@uwo.ca.

Since 2000 the available seismic stations in southern Ontario were upgraded and new stations were installed as part of the POLARIS project. By the end of 2004 and the beginning of 2005 the Combined Southern Ontario Seismic Network (CSOSN) formed a virtual seismograph network that comprised 44 stations in southern Canada, including 29 broadband stations of the Southern Ontario POLARIS Network, 4 UWO dial-up stations and 11 stations of the Canadian National Seismic Network (CNSN). The recently expanded network coverage in this region has improved the capability to detect small local and regional earthquakes. The main purpose of this study is to estimate the CSOSN detection limits for small events. One of the main factors which affects the capability of the seismic stations to detect small local and regional earthquakes are their noise characteristics, especially at frequencies above 1 Hz. Here we estimate the RMS noise level for all stations from the CSOSN in the frequency range 6 to 20 Hz at the quietest possible conditions (during the night and wind speed less than 5 km/s). The minimum RMS noise levels are used for estimation of the local and regional event detectability. The waveform samples with minimum noise RMS are also used to obtain spectra of southern Ontario POLARIS stations and compare them with Peterson's noise models. The obtained maps of the threshold magnitude of the CSOSN for 4 and 8 stations show that the lowest threshold magnitude can be detected around western Lake Ontario. Under ideal conditions, an earthquake with magnitude mN 2.0 near the center of the network would be recorded by 25 stations.