Collaborators:  Dr. John Garver (Union College, NY), Peter Reiners (Yale), David Cuevas (Master student at SLU), Mohamed El-Shafei (post-doctoral researcher at SLU)

Research Abstract:  There has been a longstanding debate regarding the strength of the San Andreas fault and other large faults in the San Andreas system.  Some field- and laboratory-derived data are consistent with these faults being anomalously weak, while other data are consistent with these faults having normal strength.  No conclusion regarding the strength of faults in the San Andreas system is supported unequivocably by the data, which has resulted in vigorous discussion among those actively working on the problem.  One of the most widely accepted and oft-quoted data in support of weak faults is the absence of anomalously high heat flow in the vicinity of these faults.  This has been coined the "stress / heat-flow" paradox.  The research outlined in this proposal will provide new data directly related to resolving the stress / heat-flow paradox by providing information regarding the paleotemperature history (and ultimately, the strength) of two large-displacement, strike-slip faults in the San Andreas system -- the Punchbowl and San Gabriel faults.
 

Specific Research Objectives

1) Determine U/Th-He and fission track apparent ages of apatites and zircons from samples collected across the Punchbowl and San Gabriel faults.

2) Model spatial distribution of apparent ages to determine the long-term average temperature profile across these faults during seismic slip and uplift/exhumation.

3) Test hypotheses regarding heat production during seismogenic slip along large strike-slip faults in the San Andreas fault system.  The results will be directly related to resolving the stress / heat-flow paradox for large-displacement faults in the San Andreas system.

4) Provide constraints for models that have been proposed to account for anomalously weak behavior of seismogenic faults in the San Andreas fault system.