HR: 14:35h
AN: S43D-04 INVITED    [Abstracts]
TI: Progress in Ambient Noise Surface Wave Measurements in the Western US
AU: Ritzwoller, M H
EM: ritzwoll@ciei.colorado.edu
AF: Center for Imaging of the Earth's Interior, Department of Physics, 390 UCB, Boulder, CO 80309-0390, United States
AU: * Moschetti, M P
EM: morganm@ciei.colorado.edu
AF: Center for Imaging of the Earth's Interior, Department of Physics, 390 UCB, Boulder, CO 80309-0390, United States
AU: Yang, Y
EM: yingjie@ciei.colorado.edu
AF: Center for Imaging of the Earth's Interior, Department of Physics, 390 UCB, Boulder, CO 80309-0390, United States
AU: Lin, F
EM: linf@ciei.colorado.edu
AF: Center for Imaging of the Earth's Interior, Department of Physics, 390 UCB, Boulder, CO 80309-0390, United States
AU: Shapiro, N M
EM: nshapiro@ipgp.jussieu.fr
AF: Laboratoire de Sismologie, CNRS, IPGP 4 place Jussieu, Paris, 75005, France
AB: Ambient noise has been shown to produce accurate surface wave dispersion maps on multiple scales over a broad period band, with resolution limited primarily by the location and spacing of instruments. The USArray Transportable Array (TA) component of Earthscope provides a nearly ideal network for carrying out ambient noise processing. Prior to USArray, much of the western United States (US) had poor station coverage. Current station spacings across the region are about 70 km, and over 400 stations return continuous data. We have carried out ambient noise surface wave measurements on emerging data from the USArray TA since October 2004 and present current short- to intermediate-period dispersion maps. Ambient noise processing produces higher resolution dispersion maps within the footprint of the USArray TA than has been possible using earthquake measurements. Resolution within the footprint of the USArray TA, and across much of the western US, now matches the average inter-station distance. Strong velocity anomalies in the dispersion maps are correlated with the Sierra Nevada, Great Valley, Peninsular and Cascade Ranges, the Columbia Basin and flood basalts, and the Snake River Plain. Recent work has demonstrated the existence of Love wave energy in the ambient noise wavefield and allows for the generation of both Rayleigh and Love wave dispersion maps. The dispersion maps provide the basis to invert for crustal and upper mantle shear-wave velocities across California and Nevada. We present a preliminary crustal and upper mantle velocity model for this region. The short- to intermediate-period dispersion measurements from ambient noise are complemented by longer-period two-plane wave measurements and result in better constraints on mantle velocities. The velocity model allows for examination of crustal structures in the Basin-and-Range, Sierra Nevada, and the hypothesized southern edge of the Juan de Fuca plate. As the USArray TA begins to roll eastward, emerging data promises to provide high resolution dispersion maps for the entire country and will allow for the construction of a single, high resolution 3D velocity model of the crust and upper mantle across the continental US.
DE: 7205 Continental crust (1219)
DE: 7255 Surface waves and free oscillations
DE: 7270 Tomography (6982, 8180)
SC: Seismology [S]
MN: 2007 Fall Meeting