Scientific Drilling Into the San Andreas Fault Zone – An Overview of SAFOD's First Five Years
The San Andreas Fault Observatory at Depth (SAFOD) was drilled to study the physical and chemical processes controlling faulting and earthquake generation along an active, plate-bounding fault at depth. SAFOD is located near Parkfield, California and penetrates a section of the fault that is moving...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2011-03-01
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| Series: | Scientific Drilling |
| Online Access: | http://www.sci-dril.net/11/14/2011/sd-11-14-2011.pdf |
| Summary: | The San Andreas Fault Observatory at Depth (SAFOD)
was drilled to study the physical and chemical processes
controlling faulting and earthquake generation along an
active, plate-bounding fault at depth. SAFOD is located near
Parkfield, California and penetrates a section of the fault that
is moving due to a combination of repeating microearthquakes
and fault creep. Geophysical logs define the San
Andreas Fault Zone to be relatively broad (~200 m), containing
several discrete zones only 2–3 m wide that exhibit very
low P- and S-wave velocities and low resistivity. Two of these
zones have progressively deformed the cemented casing at
measured depths of 3192 m and 3302 m. Cores from both
deforming zones contain a pervasively sheared, cohesionless,
foliated fault gouge that coincides with casing deformation
and explains the observed extremely low seismic velocities
and resistivity. These cores are being now extensively
tested in laboratories around the world, and their composition,
deformation mechanisms, physical properties, and
rheological behavior are studied. Downhole measurements
show that within 200 m (maximum) of the active fault trace,
the direction of maximum horizontal stress remains at a
high angle to the San Andreas Fault, consistent with other
measurements. The results from the SAFOD Main Hole,
together with the stress state determined in the Pilot Hole,
are consistent with a strong crust/weak fault model of the
San Andreas. Seismic instrumentation has been deployed
to study physics of faulting – earthquake nucleation, propagation,
and arrest – in order to test how laboratory-derived
concepts scale up to earthquakes occurring in nature.
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doi:<a href="http://dx.doi.org/10.2204/iodp.sd.11.02.2011" target="_blank">10.2204/iodp.sd.11.02.2011</a> |
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| ISSN: | 1816-8957 1816-3459 |