Passive Source Seismic Studies of the Sediments, Crust and Mantle Beneath the Nechako Basin, South-Central British Columbia (NTS 092O, 093B, C, F, G) J.F. Cassidy, Geological Survey of Canada, Victoria, BC, jcassidy@nrcan.gc.ca H. Kim, University of Victoria, Victoria, BC O. Idowu, University of Alberta, Edmonton, AB H. Kao, Geological Survey of Canada, Victoria, BC S. Dosso, University of Victoria, Victoria, BC A. Frederiksen, University of Manitoba, Winnipeg, MB J–P. Mercier, University of British Columbia, Vancouver, BC M. Bostock, University of British Columbia, Vancouver, BC A. Frassetto, University of Arizona, Tucson, AZ G. Zandt, University of Arizona, Tucson, AZ Cassidy, J.F., Kim, H., Idowu, O., Kao, H., Dosso, S., Frederiksen, Mercier, J-P., Bostock, M., Frassetto, A. and Zandt, G.A. (2010): Pas- sive source seismic studies of the sediments, crust and mantle beneath the Nechako Basin, south-central British Columbia (NTS92O, 093B, C, F, G); in Geoscience BC Summary of Activities 2009, Geoscience BC, Report 2010-1, p. 235–244. Introduction During the summer of 2006, an array of seven three- component broadband POLARIS seismic stations was de- ployed across the Nechako Basin (Figures 1a, b; Table 1). The goal of this deployment was to record large distant earthquakes, which could be used to image the Earth’s structure beneath central British Columbia. Two additional seismic stations were deployed in the autumn of 2007 to study an unusual swarm of local earthquakes near the Nazko cone (unofficial place name). The passive-source seismic datasets are being used for a wide range of studies, including · mapping the near-surface structure (e.g., sediment and volcanic cover thickness); · mapping the overall basin geometry; · estimating crustal thickness; · mapping upper-mantle structure; and · inferring flow patterns in the upper mantle based on SKS-splitting observations. Key parameters useful for resource assessment (oil, gas and mineral potential) that are obtained from these passive- source seismic datasets include S-wave velocity (sensitive to fluids and fractures), Poisson’s ratio (sensitive to lithol- ogy, porosity and fracture density), thickness of sediments and volcanic cover, and overall basin geometry (key for oil and gas potential). This report provides an update on the field operations and data collection, and briefly summa- rizes some of the applications of this passive-source seis- mic dataset to both resource assessment and improved estimates of volcanic and seismic hazards in the region. Data Collection Field Operations Deployment of the first POLARIS-Nechako seismograph stations began on August 24, 2006. Each station utilized ei- ther AC power (if available) or DC power from solar panels and provided real-time data via satellite to Geological Sur- vey of Canada (GSC) offices in Sidney, BC and Ottawa, ON. Five stations were decommissioned in 2008 and the last POLARIS station was decommissioned on August 27, 2009 (see Table 1 for details). Data Availability Waveform data are archived with data from the Canadian National Seismograph Network (CNSN) and are available in a number of ways. The easiest way to access these data is via the website: http://earthquakescanada.nrcan.gc.ca/stn don/AutoDRM/autodrm_req-eng.php. An al ter na tive method is to use the ‘AutoDRM’ service. For information on this, see http://earthquakescanada.nrcan.gc.ca/stndon/ AutoDRM/index-eng.php. Geoscience BC Report 2010-1 235 Keywords: seismic, regional geophysical survey, Nechako Basin This publication is also available, free of charge, as colour digital files in Adobe Acrobat ® PDF format from the Geoscience BC website: http://www.geosciencebc.com/s/DataReleases.asp.