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									                                                                            March 31, 2014
Greg Anderson and Jim Whitcomb
Division of Earth Sciences
The National Science Foundation
4201 Wilson Boulevard
Arlington, Virginia 22230

Dear Greg and Jim,

        We are writing to express our broad and deep interest in pursuing future scientific
opportunities made possible by the San Andreas Fault Observatory at Depth (SAFOD). SAFOD
is a globally unique facility for making a wide range of observations at seismogenic depth in a
plate boundary fault zone. NSF has invested over $20 million in drilling through the San
Andreas Fault and operating the observatory, which remains incomplete. The participation of
the scientific community in SAFOD-related research, and the impact of that research, has been
very large, with nearly 1,500 citations of published papers and meeting abstracts just since 2006,
and nearly 2,000 total (Google Scholar search, 02/07/2014). At present, the future of research
using SAFOD core samples is secure, but the future of the borehole itself and the borehole
observatory component of SAFOD appears to be endangered. There have been significant
instrumental problems in the harsh environment of the deep borehole, but with advancing
technology, those instrumental issues can be overcome. It is our opinion that NSF should
capitalize on the considerable scientific investment already made in SAFOD and establish an
operational plan and management system to keep SAFOD open for the benefit of earthquake

        In the last few years, there has been a series of community activities that have
demonstrated the broad interest in continued SAFOD science. Among these were a May 2011
two-day mini-workshop on the future of SAFOD at the EarthScope National Meeting in Austin
TX, a December 2012 lunch-time meeting at the Fall AGU Meeting in San Francisco to discuss
the future of SAFOD, and a May 2013 NSF-funded active tectonics and magmatism drilling
workshop in Park City, UT. At the first two meetings, the unique opportunities for advancing
earthquake science provided by the existing SAFOD borehole were discussed at length. At the
Park City workshop, further research utilizing the SAFOD borehole emerged as one of the high-
priority recommendations (Carpenter et al. "white paper," 2013; It seems that NSF is on the verge of
walking away from a unique science facility that can provide fundamental opportunities for
advancing earthquake science.

        What are the contributions to earthquake science that further drilling and installation of a
bona fide observatory in the SAFOD borehole would provide? Frankly, this would allow for
completion of the unmet original goals of the SAFOD science plan. Further multilateral drilling
could recover core samples from a fault patch that ruptures during repeating magnitude 1.8-1.9
earthquakes, allowing a direct comparison of the properties of the fault zone rocks where it
undergoes brittle failure to those of the nearby creeping zone sampled in 2007. Broadband, high-
sample-rate, near-field recordings of magnitude ~2 earthquakes can provide profound insights
into earthquake nucleation and rupture processes from hypocentral distances at which attenuation
is minimal and where noise is minimal. Seismic interferometry techniques will allow in-situ
monitoring of temporal changes in fault zone properties, especially in terms of earthquake
triggering observations. These are just some of the fundamental science issues that can be
addressed if we can complete the key original goals of SAFOD. We respectfully request that
NSF continue operational support for the downhole observatory and for observatory data
management, and include downhole science in the EarthScope and other RFP's.

Sincerely yours,

                                                 Gregory C. Beroza
                                                 Professor of Geophysics
                                                 Stanford University
Clifford Thurber
Professor of Geophysics
University of Wisconsin-Madison                  Terry E. Tullis
                                                 Emeritus and Research Professor
                                                 Brown University

Jean Paul Ampuero
Assistant Professor of Seismology                Roland Bürgmann
California Institute of Technology               Professor of Earth & Planetary Science
                                                 University of California, Berkeley

Yehuda Ben-Zion
Professor of Earth Sciences
University of Southern California                Paul Segall
                                                 Professor of Geophysics
                                                 Stanford University

James R. Rice
Professor of Engineering Sciences and
Geophysics, Harvard University
                                                 Emily E. Brodsky
                                                 Professor of Geophysics
                                                 University of California Santa Cruz

Thomas H. Jordan, Director
Southern California Earthquake Center            Nadia Lapusta
W. M. Keck Professor of Earth Sciences           Professor of Mechanical Engineering and
University of Southern California                Geophysics
                                                 California Institute of Technology
John Vidale
                                         Felix Waldhauser
University of Washington
                                         Adjunct Professor
                                         Lamont Doherty Earth Observatory

Zhigang Peng
Associate Professor of Geophysics        Chris Marone
Georgia Institute of Technology          Professor of Geophysics
                                         Pennsylvania State University

J Ramón Arrowsmith
Professor of Geology                     Demian Saffer
Arizona State University                 Professor of Geosciences
                                         The Pennsylvania State University

Taka’aki Taira                           Jafar Hadizadeh
Assistant Research Seismologist          Professor of Geosciences
Berkeley Seismological Laboratory        University of Louisville

Fenglin Niu                              Harold Tobin
Professor of Geophysics                  Professor of Geophysics
Rice University                          University of Wisconsin-Madison

Thomas Daley                             Herb Wang
Staff Research Scientist                 Professor of Geophysics
Lawrence Berkeley National Laboratory    University of Wisconsin-Madison

Robert M. Nadeau                         Frederick Chester
Research Geophysicist                    Professor of Geology & Geophysics
U.C. Berkeley Seismological Laboratory   Texas A&M University
Teng-fong Wong                              Allan M. Rubin
Professor of Geophysics                     Professor of Geosciences
Stony Brook University /                    Princeton University
The Chinese University of Hong Kong

                                            Heather M. Savage
Brian Evans                                 Lamont Assistant Research Professor
Professor of Geophysics                     Lamont-Doherty Earth Observatory
Massachusetts Institute of Technology

                                            Margaret Boettcher
Mark A. Zumberge                            Assistant Professor of Geophysics
Research Geophysicist                       University of New Hampshire
University of California, San Diego

                                            Robert C. Viesca
Wen-lu Zhu                                  Assistant Professor of Civil Engineering
Associate Professor                         Tufts University
University of Maryland

Rachel Abercrombie                          John M. Logan
Research Associate Professor                Courtesy Professor, University of Oregon
Boston University                           Emeritus Professor, Texas A&M University

Eric M. Dunham
Assistant Professor of Geophysics
Stanford University

CC: Paul Cutler, Acting Division Director

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