We are leading a new international initiative to conduct scientific drilling within the San Andreas fault zone at depths of up to 10 km. This project is motivated by the need to understand the physical and chemical processes operating within the fault zone and to answer fundamental questions about earthquake generation along major plate-boundary faults. Through a comprehensive program of coring, fluid sampling, downhole measurements, laboratory experimentation, and long-term monitoring, we hope to obtain critical information on the structure, composition, mechanical behavior and physical state of the San Andreas fault system at depths comparable to the nucleation zones of great earthquakes. The drilling, sampling and observational requirements needed to ensure the success of this project are stringent. These include: 1) drilling stable vertical holes to depths of about 9 km in fractured rock at temperatures of up to 300°C; 2) continuous coring and completion of inclined holes branched off these vertical boreholes to intersect the fault at depths of 3, 6, and 9 km; 3) conducting sophisticated borehole geophysical measurements and fluid/rock sampling at high temperatures and pressures; and 4) instrumenting some or all of these inclined core holes for continuous monitoring of earthquake activity, fluid pressure, deformation and other parameters for periods of up to several decades. For all of these tasks, because of the overpressured clay-rich formations anticipated within the fault zone at depth, we expect to encounter difficult drilling, coring and hole-completion conditions in the region of greatest scientific interest.

1.
Baumga¨rtner
J.
, and
Zoback
M. D.
,
1989
, “
Interpretation of Hydraulic Fracturing Pressure-Time Records Using Interactive Analysis Methods
,”
International Journal of Rock Mechanics, Mining Science and Geomechanical Abstracts
, Vol.
26
, pp.
461
470
.
2.
Brune
J. N.
,
1993
, “
Rupture Mechanism and Interface Separation in Foam Rubber Models of Earthquakes: A Possible Solution to the Heat Flow Paradox and the Paradox of Large Overthrusts
,”
Tectonophysics
, Vol.
218
,
59
67
.
3.
Brune
J. N.
,
Henyey
T. L.
, and
Roy
R. F.
,
1969
, “
Heat Flow, Stress and Rate of Slip Along the San Andreas Fault, California
,”
Journal of Geophysical Research
, Vol.
74
, pp.
3821
3827
.
4.
Byerlee
J. D.
,
1978
, “
Friction of Rocks
,”
Pure and Applied Geophysics
, Vol.
116
, pp.
615
629
.
5.
Byerlee
J. D.
,
1990
, “
Friction, Overpressure and Fault Normal Compression
,”
Geophysical Research Letters
, Vol.
17
, pp.
2109
2112
.
6.
Byerlee
J. D.
,
1993
, “
A Model for Episodic Flow of High Pressure Water in Fault Zones Before Earthquakes
,”
Geology
, Vol.
21
, pp.
303
306
.
7.
Hickman, S., 1991, “Stress in the Lithosphere and the Strength of Active Faults,” U.S. National Report to the International Union of Geodosy and Geophysics 1987–1990, Reviews of Geophysics Supplement, pp. 759–775.
8.
Hill, D. P., Eaton, J. P., and Jones, L. M., 1990, “Seismicity, 1980–86,” The San Andreas Fault System, California, ed., R. E. Wallace, U.S. Geological Survey Professional Paper 1515, pp. 115–151.
9.
Jones
L. M.
,
1988
, “
Focal Mechanisms and the State of Stress on the San Andreas Fault in Southern California
,”
Journal of Geophysical Research
, Vol.
93
, pp.
8869
8891
.
10.
Lachenbruch
A. H.
,
1980
, “
Frictional Heating, Fluid Pressure, and the Resistance to Fault Motion
,”
Journal of Geophysical Research
, Vol.
85
, pp.
6097
6112
.
11.
Lachenbruch
A. H.
, and
Sass
J. H.
,
1980
, “
Heat Flow and Energetics of the San Andreas Fault Zone
,”
Journal of Geophysical Research
, Vol.
85
, pp.
6185
6223
.
12.
Lachenbruch
A. H.
, and
Sass
J. H.
,
1992
, “
Heat Flow from Cajon Pass, Fault Strength and Tectonic Implications
,”
Journal of Geophysical Research
, Vol.
97
, pp.
4995
5015
.
13.
Magee
M. E.
, and
Zoback
M. D.
,
1993
, “
Evidence for a Weak Interplate Thrust Fault Along the Northern Japan Subduction Zone and Implications for the Mechanics of Thrust Faulting and Fluid Expulsion
,”
Geology
, Vol.
21
, pp.
809
812
.
14.
Melosh
H. J.
,
1979
, “
Acoustic Fluidization: A New Geologic Process
,”
Journal of Geophysical Research
, Vol.
84
, pp.
7513
7520
.
15.
Morrow, C., Radney, B., and Byerlee, J., 1992, “Frictional Strength and the Effective Pressure Law of Montmorillonite and Illite Clays,” Earthquake Mechanics, Rock Deformation and Transport Properties of Rocks, eds., B. Evans and T.-F. Wong, Academic Press, London, U.K., pp. 69–88.
16.
Mount
V. S.
, and
Suppe
J.
,
1987
, “
State of Stress near the San Andreas Fault: Implications for Wrench Tectonics
,”
Geology
, Vol.
15
, pp.
1143
1146
.
17.
Oppenheimer
D. H.
,
Reasenberg
P. A.
, and
Simpson
R. W.
,
1988
, “
Fault-Plane Solutions for the 1984 Morgan Hill, California Earthquake Sequence: Evidence for the State of Stress on the Calaveras Fault
,”
Journal of Geophysical Research
, Vol.
93
, pp.
9007
9026
.
18.
Rice, J. R., 1992, “Fault Stress States, Pore Pressure Distributions, and the Weakness of the San Andreas Fault,” Earthquake Mechanics, Rock Deformation and Transport Properties of Rocks, eds., B. Evans and T.-F. Wong, Academic Press, London, U.K., pp. 475–503.
19.
Rowley, J. C., 1993, “Core-Drilling Strategy and Design Concept for Ultra-Deep Scientific Projects,” ASME Paper No. 93-PET-10.
20.
Rutter
E. H.
, and
Mainprice
D. H.
,
1979
, “
On the Possibility of Slow Fault Slip Controlled by Diffusive Mass Transfer Processes
,”
Gerlands Beitrag Geophysik, Leipzig
, Vol.
88
, pp.
154
62
.
21.
Sibson
R. H.
,
1983
, “
Continental Fault Structure and the Shallow Earthquake Source
,”
Journal of the Geological Society of London
, Vol.
140
, pp.
741
767
.
22.
Sibson
R. H.
,
1992
, “
Implications of Fault-Valve Behavior for Rupture Nucleation and Recurrence
,”
Tectonophysics
, Vol.
211
, pp.
283
293
.
23.
Sleep
N. H.
, and
Blanpied
M. L.
,
1992
, “
Creep, Compaction and the Weak Rheology of Major Faults
,”
Nature
, Vol.
359
, pp.
687
692
.
24.
Stock
J. M.
,
Healy
J. H.
,
Hickman
S. H.
, and
Zoback
M. D.
,
1985
, “
Hydraulic Fracturing Stress Measurements at Yucca Mountain, Nevada, and Relationship to Regional Stress Field
,”
Journal of Geophysical Research
, Vol.
90
, pp.
8691
8706
.
25.
Wilcock
W. S. D.
,
Purdy
G. M.
, and
Solomon
S. C.
,
1990
, “
Microearthquake Evidence for Extension across the Kane Transform Fault
,”
Journal of Geophysical Research
, Vol.
95
, pp.
15439
15462
.
26.
Zoback
M. D.
, and
Beroza
G. C.
,
1993
, “
Evidence for Near-Frictionless Faulting in the 1989 (M 6.9) Loma Prieta, California, Earthquake and its Aftershocks
,”
Geology
, Vol.
21
, pp.
181
185
.
27.
Zoback
M. D.
, and
Emmermann
R.
,
1994
, “
Toward Establishing an International Continental Scientific Drilling Program
,”
Eos, Trans. Am. Geophys. Union
, Vol.
75
, p.
461
461
.
28.
Zoback
M. D.
, and
Healy
J. H.
,
1984
, “
Friction, Faulting and In-Situ Stress
,”
Annales Geophisicae
, Vol.
2
, pp.
689
698
.
29.
Zoback
M. D.
, and
Healy
J. H.
,
1992
, “
In-Situ Stress Measurements to 3.5 km Depth in the Cajon Pass Scientific Research Borehole: Implications for the Mechanics of Crustal Faulting
,”
Journal of Geophysical Research
, Vol.
97
, pp.
5039
5057
.
30.
Zoback
M. D.
,
Zoback
M. L.
,
Mount
V. S.
,
Suppe
J.
,
Eaton
J. P.
,
Healy
J. H.
,
Oppenheimer
D.
,
Reasenberg
P.
,
Jones
L.
,
Raleigh
C. B.
,
Wong
I. G.
,
Scotti
O.
, and
Wentworth
C.
,
1987
, “
New Evidence on the State of Stress of the San Andreas Fault System
,”
Science
, Vol.
238
, pp.
1105
1111
.
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