Abstract
We apply a three-dimensional (3D) generalized Radon transform (GRT)
to scattered P-waves from 575 local earthquakes recorded at 68 temporary
network stations for passive-source imaging of (near-vertical) structures
close to the San Andreas Fault Observatory at Depth (SAFOD) site.
The GRT image profiles through or close by the SAFOD site reveal
near-vertical reflectors close to the fault zone as well as in the
granite to the southwest and the Franciscan mélange to the northeast
of the main fault. Although slightly lower in resolution, these structures
are generally similar to features in 2D images produced with steep-dip
prestack seismic migration of data from active source seismic reflection
and refraction surveys. Our GRT images, however, also reveal several
vertical reflectors to the northeast of the SAF that do not appear
in the migration images but which are consistent with local geology.
These results suggest that in a seismically active area, inverse
scattering of earthquake data (for instance with the GRT) can be
a viable and, in 3D, economic alternative to an active source survey.
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