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What Can the Thermal History of Parkfield Tell Us About the Mechanics of the San Andreas Fault?: Matthew A. d'Alessio


Project Title: What Can the Thermal History of Parkfield Tell Us About the Mechanics of the San Andreas Fault?
Mendenhall Fellow: Matthew A. d’Alessio, (650) 329-4829, dalessio@usgs.gov
Duty Station: Menlo Park, CA
Start Date: October 4, 2004
Education: Ph.D., U. of California at Berkeley, 2004
Research Advisors: Colin Williams (650) 329-4881, colin@usgs.gov; Stephen Hickman (650) 329-4807, hickman@usgs.gov
  Matthew  A. d'Alessio

Project Description: Faults live and die by their frictional properties. Friction determines how and when faults slip, how faults interact with each other, influences fault geometry, and affects stresses in the rocks around faults. For more than thirty years, debate has raged about the frictional strength of natural faults such as the San Andreas. Because frictional sliding generates heat, the most direct measure of a fault’s frictional strength can come from detailed observations of the thermal regime around it. While such heat flow observations have been made in the past, a number of other processes such as exhumation, uplift, and burial by sediments can alter the thermal regime near active faults. In this study, I strive to characterize and quantify the effect of these other processes, as well as come up with more realistic predictions of frictional heat generation along faults by including the effects of fault zone heterogeneity on the magnitude and distribution of heating.

I focus my efforts on the central section of the San Andreas fault near the town of Parkfield, California, where a 3.5 km deep borehole will penetrate through the fault. This “San Andreas Fault Observatory at Depth” (SAFOD) provides an unprecedented opportunity to explore the thermal history of the region using direct measurements of heat flow and constraints from a suite of thermochronometers (analyses of rock samples that can reveal their thermal history using radiometric dating) across a range of depth intervals. I will use these observations along with computer modeling to generate a complete thermal history of the region, hoping to eventually determine the relative contribution of uplift, erosion, burial, and frictional heat along the San Andreas fault.

View of the San Andreas fault near Parkfield, California. The SAFOD drill site is 1.8 km southwest of the fault.   Preliminary thermal history of a sample from the SAFOD borehole from 4800 ft (1463 m) below the ground.
View of the San Andreas fault near Parkfield, California. The SAFOD drill site is 1.8 km southwest of the fault.
  Preliminary thermal history of a sample from the SAFOD borehole from 4800 ft (1463 m) below the ground.

I also promote enthusiasm for earth science by participation in educational outreach projects. My employment with the USGS spans the Centennial of the Great San Francisco Earthquake of 1906, and the entire Bay Area is gearing up for a lot of emphasis on earthquake science during the centennial year. Through my work with middle school curriculum development and classroom visits, I hope to inspire the next generation of earth scientists while I simultaneously bolster my own passion for our science.


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Last modified: 16:08:27 Thu 13 Dec 2012