1. Steep-dip seismic imaging of the shallow San Andreas fault near Parkfield
- Author
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Hole, J.A., Catchings, R.D., St. Clair, K.C., Rymer, M.J., Okaya, D.A., and Carney, B.J.
- Subjects
San Andreas Fault -- Natural history ,Usage ,Research ,Natural history ,Seismic reflection surveying -- Usage -- Research ,Earthquake prediction -- Research -- Usage ,Seismic reflection method -- Usage -- Research - Abstract
Determination of the structure and internal properties, such as geometry, mineralogy, and fluid content, of fault zones is essential to understanding the earthquake process. Exposed faults provide constraints on fault [...], Seismic reflection and refraction images illuminate the San Andreas Fault to a depth of 1 kilometer. The prestack depth-migrated reflection image contains near-vertical reflections aligned with the active fault trace. The fault is vertical in the upper 0.5 kilometer, then dips about 70 ldegrees] to the southwest to at least 1 kilometer subsurface. This dip reconciles the difference between the computed locations of earthquakes and the surface fault trace. The seismic velocity cross section shows strong lateral variations. Relatively low velocity (10 to 30%), high electrical conductivity, and low density indicate a 1-kilometer-wide vertical wedge of porous sediment or fractured rock immediately southwest of the active fault trace.
- Published
- 2001