HR: 09:45h
AN: T21D-08    [Abstracts]
TI: Lithospheric Structure Across the Cordillera-Craton Transition in NW Canada From Surface Waves Traversing the CANOE Array
AU: * Gaherty, J B
EM: gaherty@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964 United States
AU: Wilson, C K
EM: wilsonck@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964 United States
AU: Zhao, L
EM: zhaol@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, Taipei, 115 Taiwan
AB: The Canadian Northwest Experiment (CANOE) is a nearly sixty-station broadband PASSCAL array extending from the Slave Craton in the Canadian NWT, across the Canadian Rockies in northern British Columbia and Yukon and south to Edmonton, Alberta. The array crosses a series of compressive orogens that span 4 Ga of geologic time and are undisrupted by later periods of extension or extensive volcanism. With a nominal station spacing of approximately 50 km, CANOE offers an unparalleled opportunity to image the structural expression of the accretion of continental lithosphere through time. In this study, we utilize surface waves traversing the CANOE array to constrain the anistropic shear-velocity structure of the crust and upper mantle across the cordillera-craton transition. A cross-correlation procedure is used to measure the relative frequency-dependent travel times of Love and Rayleigh waveforms across the array. The data are derived from recordings of over 140 earthquakes (Mw >6, epicentral distances <100°) recorded between June 2004 and Sept 2005, as well as interstation cross-correlation of ambient seismic noise between the array stations. The earthquake-generated waveforms provide measurements in the 5-60 mHz band, sufficient to image mantle structure to depths of up to 300 km, while the noise cross-correlations provide data in the 50-100 mHz band, allowing us to image crustal velocity and thickness variations across the region. Using accurate three-dimensional sensitivity kernels, these data are combined in a 3D tomographic inversion for anisotropic shear-velocities in the crust and upper-mantle across the transition from craton to cordillera. Variations in isotropic shear velocity across the region primarily reflect the thermal history, while radial and azimuthal anisotropy will be used to characterize lithospheric fabric. The surface-wave observations will be integrated with receiver function and shear-wave splitting data, providing a comprehensive portrait of lithospheric structure across the transition.
DE: 7218 Lithosphere (1236)
DE: 7255 Surface waves and free oscillations
DE: 7270 Tomography (6982, 8180)
DE: 8103 Continental cratons
SC: Tectonophysics [T]
MN: Fall Meeting 2005