High-resolution shallow structure revealed with ambient noise tomography on a dense array
Abstract
A dense seismic array was deployed by the PoroTomo research team at Brady Hot Springs, Nevada in March 2016. The array consisted of 238 short-period three-component geophones (5-Hz corner frequency) with about 60 m spacing. Over the 15 day deployment, the array recorded over 6,000 active source signals (vibroseis sweeps) and ambient noise that was dominated by traffic noise.We adopted the one-bit method to better reduce the effect of the active source. Spectral whitening was performed between 0.5 and 2 Hz. The continuous record was chopped into 1 minute segments. The 1-minute cross-correlation functions were initially stacked linearly, and then the phase-weighted stacking method was applied to improve signal quality. More than two million noise correlation functions (NCFs) have been obtained.The Rayleigh wave group velocity was measured on the symmetric component of the NCFs with the frequency-time analysis method. The average group velocity is about 400 m/s at 4 Hz, which is consistent with preliminary active source result. To avoid mis-picking possible precursors, the arrival time was picked at the peak in a two-second time window predicted with the average group velocity of the fundamental mode. The quality of the arrival measurements is defined by the signal-to-noise ratio. We were able to pick reliable arrivals at about 35% of the station-pairs. Since the straight-ray assumption may not be valid in a strongly heterogeneous medium, the wave path was traced with a finite difference scheme and the LSQR method was utilized to invert group velocity. The heterogeneous features of the group velocity map are consistent with a local geologic map. The PoroTomo project is funded by a grant from the U.S. Department of Energy.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.S13B2574Z
- Keywords:
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- 7203 Body waves;
- SEISMOLOGYDE: 7219 Seismic monitoring and test-ban treaty verification;
- SEISMOLOGYDE: 7255 Surface waves and free oscillations;
- SEISMOLOGYDE: 7294 Seismic instruments and networks;
- SEISMOLOGY