Testing Fundamental Theories of Earthquakes and Faulting: 
The San Andreas Fault Observatory at Depth

Mark D. Zoback (1), Stephen H. Hickman (2), William L. Ellsworth (2)
(1) Department of Geophysics, Stanford University, Stanford, CA 94305
(2) U.S. Geological Survey, Menlo Park, CA 94025

ABSTRACT

On September 16, 2004, the San Andreas Fault Observatory at 
Depth (SAFOD) reached the planned total depth for Phase 1. 
After drilling vertically to a depth of ~ 1.5km at a site 
1.8 km from the San Andreas Fault, the SAFOD drillhole is 
now deviated 54 degrees from vertical and has drilled 1.1 
km toward the San Andreas fault, aiming directly at a patch 
of fault producing repeating M~2 microearthquakes at 3 km 
depth. The current vertical depth of the hole is 2.5 km. 
During drilling, gas emanations (He, CO2, CH4, H2, Rn, etc.) 
were continuously monitored, cuttings from the well were 
sampled at 3 m intervals, cores have been obtained from 
two depths and comprehensive geophysical measurements have 
been carried out in the hole. All data obtained to date are 
consistent with the weak fault imbedded in a 
strong crust model of the San Andreas fault. 
The initial phases of construction of a multi-stage, 
multi-component geophysical observatory have been carried out.