Conveners: Brett Carpenter, Clifford Thurber, Bill Ellsworth
Location: Stanford University
Date of Workshop: October 12-14, 2018
The SAFOD project recovered core samples from the Pacific-North America plate boundary and creeping patches of the San Andreas Fault, within about 100 m of a magnitude ~2 repeating earthquake patch. Data gathered on samples returned from depth have provided explanations for the weakness and aseismic behavior of the fault. Furthermore, samples collected from depth have shown the degree that fluid-rock interaction plays in the evolution of fault zone behavior. Finally, samples have also shown a past, seismic history for rock currently in the creeping section of the SAF. Borehole instruments has have subsequently obtained a substantial archive of seismic data for earthquakes, tremor, and low frequency earthquakes along the San Andreas fault zone, as well as years of interferometric vertical strainmeter data. Borehole measurement results have highlighted the structure of the fault zone, that evolution of the state of stress approaching a plate boundary fault, and the role of crustal fluids in fault zone behavior. Finally, surface and borehole seismology studies have resulted in the detailed characterization of repeating earthquake clusters, the observation of preseismic velocity changes, and a better understanding of the 3D crustal structure surrounding the fault.
Overall SAFOD sampling, down-hole measurements and instrumentation at seismogenic depths have produced significant advances in our understanding of fault zone evolution, structure, composition and behavior. The project provided critical information on fundamental science goals in 2001 Earthscope Project Plan. SAFOD provided "the first look at the inner workings of a portion deep within an active geosystem - the San Andreas fault," and measured "subsurface conditions that give rise to slip on faults and deformation in the crust." However, a series of critical unknowns still exist.
The workshop would bring together key participants with the following goals:
1) Synthesize the key scientific outcomes from SAFOD science
2) Review the data/techniques that formed early predictions for the SAFOD project and their correctness
3) Develop a plan to apply SAFOD data to existing concerns surrounding earthquake hazard along creeping faults and the physics of earthquake nucleation. Such a development would also consider possible future research utilizing SAFOD data and the SAFOD facility.