HR: 10:45h
AN: S52A-02 INVITED    [Abstracts]
TI: Broad-band Measurement and Inversion of Interstation Surface-Wave Dispersion
AU: * Lebedev, S
EM: sergei@geo.uu.nl
AF: Utrecht U, Earth Sci, Utrecht, 3584CD, Netherlands
AU: Meier, T
EM: meier@geophysik.rub.de
AF: Ruhr U, GEO, Bochum, 44780, Germany
AB: We present a novel combination of waveform analysis techniques for accurate, broad-band interstation measurement of surface-wave phase velocities. We first measure the fundamental-mode dispersion between a pair of stations by cross-correlating seismograms from the stations (Meier et al. GJI 2004). Waveforms observed at short periods (10-20 s) are complex, distorted by diffraction. It turns out, however, that patterns of waveform complexity often change little as seismic waves propagate from one station to another nearby; cross-correlation can extract accurate measurements even from signals that appear prohibitively complex. We then measure average phase velocities between sources and stations by means of the Automated Multimode Inversion (AMI) of surface- and S-wave forms (Lebedev et al. GJI 2005), and calculate interstation dispersion from each pair of measurements (same event, both stations). AMI synthesizes complete seismograms, and fundamental-mode dispersion can be measured even when the mode interferes with energetic S waves. The cross-correlation technique thus provides short-period measurements and the multimode-waveform technique yields more longest-period measurements, especially for Love waves. Robust dispersion curves with error estimates are derived by averaging over tens or hundreds of smooth curves measured using different events. Any one-event measurement can be biased due to diffraction. Selection of only smooth portions of the curves, removal of outliers, and averaging over many curves obtained with earthquake signals from different regions and from different directions combine to enhance the accuracy of the measured dispersion. Applications of the method to permanent-station data produced measurements in period ranges 10-300 s and broader, with resolving power for isotropic and anisotropic structure from the upper crust to deep upper mantle. S-velocity profiles can be computed from the data by solving small, well-determined inverse problems. Using series of target tests, we can also explore the model spaces of the inverse problems and derive robust ranges of seismic structure parameters consistent with the data. We present results of measurements and inversions for stable and active continental regions, with inferences on structure and dynamics of the lithosphere and asthenosphere.
DE: 7218 Lithosphere (1236)
DE: 7255 Surface waves and free oscillations
DE: 7260 Theory
SC: Seismology [S]
MN: 2007 Fall Meeting