Helmholtz Centre Potsdam
GFZ German Research Centre for Geosciences
Abstract (EDOC: 7042)
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.
(2004): Seismic and magnetotelluric interpretation near Parkfield, California: Testing a joint inversion of independet data sets. AGU 2004 Fall Meeting (San Francisco 2004), GP11A-0824.