HR: 1340h
AN: S33A-1071    [Abstracts]
TI: Wide-Angle Controlled-Source Receiver Functions
AU: * Morozov, I B
EM: igor.morozov@usask.ca
AF: University of Saskatchewan, 114 Science Place , Saskatoon, SK S7N5E2 Canada
AB: Receiver function (RF) methodology has become an accepted standard for imaging the Moho, upper mantle, and sometimes crustal discontinuities. However, its present applications to teleseismic waves and deep structures contain virtually no means for independent confirmation of RF images by methods of comparable accuracy, and the resulting images are typically validated on the basis of their geodynamical plausibility. Such lack of corroboration could be partly resolved by an application of RF techniques in controlled-source seismology. Recently, we constructed RFs from the recordings from an ultra-long-range refraction profile QUARTZ in Northern Eurasia and showed that the converted P/S waves could be utilized to map the thickness of the sediments along the profile and to estimate their Poisson's ratio. Here, I present a further application of RF techniques to a high-quality wide-angle crustal dataset acquired in 1994 as a part of ACCRETE project in SE Alaska and Coastal British Columbia. The dataset included 1700 km of marine multichannel (MCS) profiling in BC fjords that were also recorded by ~40 three-component Reftek seismographs deployed at 3-5 km spacing on land. From the perspective of converted-wave studies, this dataset provides thousands of RFs recorded from a highly consistent airgun source fired at 50-m spacings. Three-component particle motion analysis and RF deconvolution reveal consistent P/S mode conversions in the first arrivals in nearly all ACCRETE receiver gathers. Particle motion changes from linear (primary P-wave) to circularly-polarized transverse (P/S converted mode) within 100-200 ms milliseconds of the first arrivals. Notably, and similarly to what had been observed in QUARTZ records, the amplitudes of P/S converted modes exceed those of the first arrivals. Although the RFs for the same receiver are generally consistent, notable variations occur, apparently due to the interplay of scattering modes and the effects of crustal velocity heterogeneities. The locations of P/S converting boundaries (or scatterers) were estimated from the time delays and polarizations of the converted waves. These results suggest that, also similarly to QUARTZ, ACCRETE mode conversions take place on the sediment-basement contact which was mapped in the MCS profiling. Thus, identification of mode conversions in the coda of wide-angle first arrivals helps constraining the shallow near-receiver structure. In addition, such analysis provides valuable experimental data on the factors controlling RF consistency.
DE: 7294 Instruments and techniques
DE: 7299 General or miscellaneous
DE: 7218 Lithosphere and upper mantle
DE: 3025 Marine seismics (0935)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting