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Poster, 13. - 17. December
DDC:
550 - Earth sciences
Abstract:
We present a simultaneous interpretation of coincident magnetotelluric (MT) and seismic refraction lines near the Parkfield, CA, San Andreas Fault Observatory at Depth site. The MT data set was acquired with Phoenix 4-channel systems with average station spacing of about 250 m over a profile length of ($sim$5000) m. The time-domain recording scheme was designed to yield data in the 0.01-200 Hz frequency band. The seismic travel-times were obtained from a SAFOD-related refraction/reflection line that was shot in the fall of 2003. The station and shot spacing for the line section coincident with the MT data were 50~m and 500~m, respectively. An initial, first-pass model of the seismic data suggests a simple structure lies beneath the study site: a 1.0-1.5 km thick, gradational, sedimentary layer with surface topography over a more uniform igneous basement. Modeling of the MT data alone shows a significant trade off exists in these data between the sediment thickness and the basement resistivity. To integrate the separate seismic and MT interpretations we combine both data sets into a joint inversion scheme by assuming that rapid velocity changes are accompanied with correspondingly rapid resistivity changes. We expect the combination will yield a mutually consistent estimate of sediment thickness and basement topography beneath the studied line.
