HR: 0800h
AN: S41B-0556 [Abstracts]
TI: Shear-Wave Splitting in the Great Basin
AU: * West, J D
EM: john.d.west@asu.edu
AF: Arizona State University, PO Box 871404, Tempe, AZ 85287, United States
AU: Fouch, M J
EM: fouch@asu.edu
AF: Arizona State University, PO Box 871404, Tempe, AZ 85287, United States
AB:
The Great Basin region of western North America has undergone as much as 200% extension over the past 20
M.y., in a predominantly east-west direction. The goal of this study is to better understand the causes and
processes for wide spread extension in the region. To this end, we present results of anisotropic structure
imaging via shear wave splitting analyses using both long-lived stations and the USArray Transportable Array
(TA). Over 75 TA stations exist in the region with data spanning back to February 2006, while 8 permanent
broadband stations in the Great Basin have recorded data for over 14 years. We processed seismic waveforms
for SKS splitting analysis using a combination of the rotation-correlation, minimum energy, and eigenvalue
methods.
Initial results for this study exhibit predominantly east-west fast polarization directions across the northern and
central Great Basin, consistent with both the primary direction of extension and with the direction of plate motion
in a global hotspot reference frame. However, fast directions at most stations exhibit significant variations over
short interstation distances (16 km to 24 km) and over small changes in back azimuth. Splitting times range from
0.1 to 2.2 seconds, and average approximately 1.0 sec. Some variability in splitting times between stations was
observed; southerly stations (TPH and TPNV) exhibited significantly smaller splitting times than were observed
elsewhere.
The combination of strongly varying fast polarization directions and large splitting times is indicative of a complex
anisotropic structure that varies both laterally and with depth, likely caused by a combination of lithospheric and
asthenospheric structures. Candidate complexity styles include multiple layers of anisotropy, dipping layers,
and/or small scale heterogeneities in subsurface structure. To elucidate the nature of the anisotropic complexity,
we are currently engaged in further study by expanding our shear-wave splitting analysis to include recent data
from all USArray stations in the Great Basin, as well as using receiver function analysis to provide better
constraints on the nature of vertically varying structures.
DE: 7205 Continental crust (1219)
DE: 7218 Lithosphere (1236)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8109 Continental tectonics: extensional (0905)
DE: 9350 North America
SC: Seismology [S]
MN: 2007 Fall Meeting