Mapping Crustal Structures of the Nechako Basin Using Teleseismic Receiver Functions

This poster describes a passive-source seismic mapping project in the Nechako Basin of central British Columbia (BC), Canada, with the goal of assessing the hydrocarbon and mineral potential of the region. An explosion of the mountain pine beetle population in central BC over the last decade has devastated the lodgepole-pine forest industry on which many communities depend. Mineral or energy extraction may provide an alternative economic opportunity for the region. The Nechako Basin has been the focus of limited hydrocarbon exploration since the 1930s. Twelve exploratory wells were drilled; oil stains on drill chip samples and the evidence of gas in drill stem tests indicate the presence of a hydrocarbon system. The basin contains mainly Mesozoic sedimentary and volcanic rocks which are blanketed by Eocene and Neogene volcanic rocks. Because only limited seismic energy is able to penetrate this hard volcanic cover, seismic data collected in the 1980s are generally of poor quality. The present study utilizes recordings of distant earthquakes at an array of seven broadband seismic stations deployed over much of the basin in September, 2006. Receiver functions are calculated from the recorded teleseismic waveforms by deconvolving the radial components with the vertical components, and subsequently inverted for shear-wave velocity structure using the Neighborhood Algorithm. Preliminary results indicate that the crustal thickness of the basin is about 40 km with a low velocity zone at around 20-30 km depth and low-velocities near the surface, which may represent the existence of sediments. This study will complement independent active- source seismic studies planned for the region by providing site-specific images and constraints on the shear- wave structures. This study will also complement magnetotelluric measurements currently underway, providing critical new information on porosity, fractures, and fluids.