ABSTRACT
There is evidence for low frictional strength along many plate-boundary faults, including the San Andreas and the Cascadia subduction megathrust. High pore pressure is a leading hypothesis to explain this behavior. Proposed mechanisms for generating excess pore pressures include consolidation, tectonic strain, metamorphic dehydration, mantle degassing, hydrocarbon generation, thermal expansion, and pressure solution. Regional-scale flow and transport models constrained by observations of fluid chemistry, heat flow, and pore pressure data can be used to test various pressure generation hypotheses. Ultimately, these results may be coupled to models of other processes such as frictional heating or strain to understand the importance of fluids.

ABOUT THE SPEAKER
Barbara Bekins of the U. S. Geological Survey (USGS) has been selected as the 2004 Birdsall-Dreiss Distinguished Lecturer, sponsored by the GSA Hydrogeology Division and funded by the GSA Foundation.

After studying both geology and mathematics, Bekins received a B.A. in Mathematics from University of California, Los Angeles. She worked for eight years as a computer specialist in the Seismology Branch of the USGS, and studied part-time to earn an M.S. in Mathematics from San Jose State University. She then left the USGS to pursue Ph.D. studies at University of California, Santa Cruz, under the direction of Shirley Dreiss. Dreiss was the 1992 GSA Birdsall lecturer and the lectureship was renamed “Birdsall-Dreiss” after her untimely death in 1993.

Bekins’ thesis research focused on numerical modeling of groundwater flow and solute transport in the Barbados subduction zone. After completing her Ph.D. she obtained a post-doctoral position at the USGS, modeling the biodegradation of groundwater contaminants with funding from the Environmental Protection Agency. In 1997, she joined the USGS staff as a Research Hydrologist in Menlo Park, California. From 1998-2000, she was a member of the National Research Council’s Committee on Intrinsic Remediation. The committee’s report “Natural Attenuation for Groundwater Remediation,” describes the capabilities of natural attenuation and the adequacy of the published guidelines for demonstrating its effectiveness. Bekins has also sailed as a shipboard scientist on Ocean Drilling Program Leg 171A to the Barbados subduction zone in 1997, and Leg 201 to the Peru Margin in 2002. More recently, she has been working with the USGS National Water Quality Assessment program on the fate of agricultural chemicals in the subsurface.

Bekins’ current research interests encompass two broad areas. The first is the role of groundwater along plate-boundary faults, including effects of pore pressure on fault strength and the use of natural tracers to understand regional flow systems. The second research area involves the effects of groundwater flow and aquifer properties on subsurface microbial activities including natural attenuation of contaminants.