James P. Evans Talk Summary

James P. Evans Talk Summary

Professor, Utah State University [in place of Mark D. Zoback]

The San Andreas Fault Observatory at Depth [SAFOD] is part of the National Science Foundation’s Earthscope initiative and tests fundamental questions regarding earthquake and fault mechanics [Hickman et al., 2004; http:/www.icdponline.de/sites/

sanandreas/index/]. In addition to numerous geophysical applications, the project also provides an opportunity to directly sample rocks related to active faults at depth. One of the primary objectives of the SAFOD project is to determine the structure and composition of the active San Andreas Fault zone at depths where earthquakes nucleate. A wide range of data collected from 2002-2007 in two closely spaced boreholes (roughly 15 m map distance separation) at the SAFOD drill site, near Parkfield, California provides insights into fault zone properties. These data, along with measurements of in situ stress, permeability and pore pressure conditions, analyses of frictional behavior of fault zone materials, and the determination of physical properties and chemical processes in the fault zone, will help constrain the behavior of seismogenic and creeping faults.

Our AAAS talk will provide an overview of the most recent results of SAFOD –related work that provide insights into the nature of active faults. I will discuss the latest results of the analyses of faulted rocks from cores across the active trace at 3 km depth, very near-field geophysical studies of the fault zone, including a portion of the fault that creeps at 2-3 cm/year, and studies of earthquake processes in which seismometers were located 100’s m from the earthquakes, rather than the traditional far-field locations. Many of the papers that discuss this work are in review, and we will summarize their results as well as recently published work in Bradbury et al., 2007; Solum et al., 2007, Bennington et al., 2008, and Draper et al., in review.

Bennington, N., Thurber, C., and Roecker, S., Three-Dimensional Seismic Attenuation Structure around the SAFOD Site, Parkfield, California Bulletin of the Seismological Society of America, Dec 2008; 98: 2934 – 2947.

Bradbury, K.K., Barton, D. C., Draper, S. D., Solum, J. G., and Evans, J. P., 2007, Mineralogic and textural analyses of drill cuttings from the San Andreas Fault Observatory at Depth (SAFOD) boreholes: Initial interpretations of fault zone composition and constraints on geologic models: Geosphere. v. 3, # 5, p. 299-318, DOI: 10.1130/GES00076.1.

Draper, S. D., Evans, J. P., Garver, J., and Kirschner, D.S., Arkosic sedimentary rocks along the San Andreas fault at SAFOD, and implications for the tectonics of the San Andreas fault, to: Lithosphere.

Hickman, S., Zoback, M. D., and Ellsworth, W., 2004, Introduction to special section:

Preparing for the San Andreas Fault Observatory at Depth, Geophysical Research

Letters, 31, L12S01, doi:10.1029/2004GL020688.

Hickman, S., Zoback, M. D., Ellsworth, W. L., 2005, Structure and Composition of the

San Andreas Fault Zone at Parkfield: Initial Results from SAFOD Phases 1 and 2,

Eos Trans. AGU, 86(52), Fall Meet. Suppl., Abstract A T23E-05.

Solum, J. G., Hickman, S. H., Lockner, D. A., Moore, D. E., van der Pluijm, B. A., Schleicher, A. M., and Evans, J. P., 2007, Mineralogy of protolith and fault rocks from the SAFOD main hole, Geophys. Res. Lett.doi: 10.1029/2006GL027285.