HR: 1340h
AN: S33A-1041    [Abstracts]
TI: An Investigation of Lithospheric Thickness Beneath Stations of the Canadian National Seismographic Network
AU: * Schaeffer, A
EM: aschaeffer@eos.ubc.ca
AF: Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4, Canada
AU: Bostock, M
EM: bostock@eos.ubc.ca
AF: Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4, Canada
AB: Recent studies have identified Sp conversions as a promising tool for characterizing the Lithosphere/Asthenosphere Boundary (LAB). The S-receiver function holds advantage over more conventional P- receiver functions since the conversions arrive within a time window that is free of crustal multiples. The disadvantage is the greater background level of signal generated noise and a more restricted selection of suitable events. We have assembled an S-wave data set from the Canadian National Seismograph Network to identify and characterize the depth of the LAB across Canada. S-receiver functions for each station are generated by transformation of particle velocity to upgoing wavefield components, followed by least-squares deconvolution. Signal quality is monitored through a culling of data whose signal-to-noise ratio lies below 65 dB based on the log variance before and during the direct S-arrival. A summary depth profile is generated by stacking receiver functions along predicted travel time curves for a 1-D model. The method has been calibrated through comparison with recently published results on LAB signals at other locations around the globe. On average there ~40 S-receiver functions per station corresponding to epicentral distances between 55° and 85° to minimize interference with SKS and ScS. Back-azimuthal coverage is geographically limited to three distinct sectors, the North-West Pacific, South America, and the Himalayas. Our initial focus is on the transition from North American Cordillera to Canadian Shield across western Canada, where a large and abrupt change from thin to thick lithosphere is expected on the basis of previous elastic thickness, surface wave, and heat flow investigations. Preliminary results from our data set indicate clear Moho arrivals at depths consistent with those determined from P-receiver functions. Arrivals at times and slownesses consistent with an origin near the base of the lithosphere are also evident at some stations. The nature of these signals and their relationship to the LAB will be discussed.
DE: 7218 Lithosphere (1236)
SC: Seismology [S]
MN: 2007 Fall Meeting