Organizers: James P. Evans, Yehuda Ben-Zion, Judith Chester, Thomas Rockwell

This workshop will focus on measurements and interpretations concerning the distribution and origin of intensely fractured (i.e., pulverized) rock along the active trace of the San Andreas and other faults, and the implications of these faulting products to rupture propagation, rupture directivity and the earthquake energy balance. The key questions for discussion include:

• What conditions of faulting favor pulverization of rock?
• Is this fault rock another indicator of seismic rupture?
• What are the dimensions of the pulverized zone? How deep does it extend and what controls the depth of the lower boundary?
• If asymmetrically disposed about the principal fault surface, what is the origin of this asymmetry?
• How much energy is consumed by pulverization?
• Do mechanical and chemical weathering processes in the near-surface environment enhance the breakdown of fractured rock and promote the development of a pulverized character?
• What are the in situ elastic and seismic attenuation properties of these fault zone rocks?
• What can be inferred from fault zone structure regarding the mode, level of dynamic stresses, and other characteristics of earthquake rupture?
• How do observed variations in damage, mineralogy, and chemistry in fault zones correlate with geophysical measures of physical and mechanical properties?
• What is the exact nature and process of pulverization, and what are the best methods to standardize documentation?
• Do all rock types produce the same damage signatures, or do some types favor pulverization while others accommodate large strain by other mechanisms?
• How does rock pulverization depend on the fluid, temperature and geochemical environment of fault zone rocks?
• Can shallow drilling into a fault zone answer some of the above key issue?

The workshop will consist of a day field trip to the Mojave section of the SAF (Saturday, September 9), followed by a 3/4 day with oral presentations (Sunday, September, 10). The field trip will focus on several observable aspects of pulverized and damaged rocks including:

• Characteristics of pulverized rocks in the outcrop and hand-sample scales.
• Susceptibility of various rock types to pulverization and other observed styles of deformation within the fault zone.
• Symmetry properties of the pulverized rock body with respect to the slipping zone.
• The structure of the pulverized rock body (width), fault-normal pulverization gradient.
• Indications for the depth extent of pulverization.

Tentative time table:

• The stations will include road side outcrops as well as short and relatively easy hikes, up to 1 km long.
• Light lunch and water will be provided.
• Recommended equipment: comfortable walking shoes, hat, sunscreen. Snacks if you wish. Geologic hammer and a hand magnifying glass can be helpful.

We anticipate the following format for the Sunday presentations:

1. Introduction
2. Goals and objectives of Workshop
3. Fault zone structure, composition and occurrence of pulverized rocks
4. Geophysical investigations (MT, gravity) of pulverized zones
5. Seismological investigations (earthquakes, guided waves)
6. Active source experiments, geophysical surveys active and passive source studies, GPR
7. Drilling strategies core sample recovery and analyses
8. Scientific issues that this drilling initiative could address
9. Overview of DOSECC equipment, procedures
10. Science planning -- defining objectives
11. Geologic investigations of core
12. Geophysical investigations
13. Long term instrument deployment issues
14. Existing infrastructure, etc.
15. Drill site characteristics and drilling strategy (e.g., single versus multiple holes)

If you have any questions please contact one of the following:

Ory Dor, dor(at)usc.edu
Tom Rockwell, trockwell(at)geology.sdsu.edu
Jim Evans, jpevans(at)cc.usu.edu
Judi Chester, chesterj(at)geo.tamu.edu