Drilling into the San Andreas Fault.

Geophysicists from Stanford University, the U.S. Geological Survey, and the Department of Energy are planning a 10-year experiment to drill holes as deep as 10 kilometers (6.2 miles) directly into the San Andreas Fault. The experiment not only would help resolve mysteries about how the fault works and why it seems to be under much less stress than scientists thought it should be, it would monitor what happens during and between earthquakes, explains Mark Zoback, chairman of Stanford's geophysics department and one of the co-investigators of the proposed experiment.

According to the proposal, the geophysicists would drill vertical holes at one site along the fault using technology developed as part of ultra-deep scientific drilling efforts in Germany. The holes would go straight down at first and then--at depths of three, six, and nine kilometers--be aimed diagonally through the fault itself. As the holes are drilled, the scientists would use the core samples to analyze the composition of the fault zones. Once inside the fault zone, casing would line the borehole and fluid samples would be taken through holes in the casing. The main task of the experiment would be to find out why the fault zone is as weak as it is. Studies by Zoback and others have...