The Town of Parkfield, located on the San Andreas fault in central California, has been the site of an intensive, multidisciplinary earthquake study since the late 1970's. The goal is to observe the fault and surrounding crust at close range at the time before, during and after an earthquake, to better understand the earthquake process and provide a scientific basis for earthquake prediction. Close- up map of Parkfield study area.

The Parkfield Experiment is a comprehensive, long-term earthquake research project on the San Andreas fault. Led by the USGS and the State of California, the experiment's purpose is to better understand the physics of earthquakes - what actually happens on the fault and in the surrounding region before, during and after an earthquake. Ultimately, scientists hope to better understand the earthquake process and, if possible, to provide a scientific basis for earthquake prediction. Since its inception in 1985, the experiment has involved more than 100 researchers at the USGS and collaborating universities and government laboratories. Their coordinated efforts have led to a dense network of instruments poised to "capture" the anticipated earthquake and reveal the earthquake process in unprecedented detail.

Hypothesis: Moderate-size earthquakes of about magnitude 6 have occurred on the Parkfield section of the San Andreas Fault at fairly regular intervals - in 1857, 1881, 1901, 1922, 1934, and 1966. The first, in 1857, was a foreshock to the great Fort Tejon earthquake which ruptured the fault from Parkfield to the southeast for over 180 miles. Available data suggest that all six moderate-sized Parkfield earthquakes may have been "characteristic" in the sense that they all ruptured the same area on the fault. If such characteristic ruptures occur regularly, then the next quake would have been due before 1993. However, the predicted earthquake still has not occurred (as of June, 2002). Current estimates of the likelihood of the next Parkfield earthquake are about 10% per year.

These pages describe the scientific background for the experiment, including the tectonic setting at Parkfield, the historical earthquake activity on this section of the San Andreas fault, the monitoring and data collecting activities currently being carried out, and plans for future research. Data are available to view in real-time and download.

Scientific Advances: While the greatest scientific payoff is expected when the earthquake occurs, our understanding of the earthquake process has already been advanced through research results from Parkfield. Some of the highlights are described.

Data: Real-time data from instrumentation networks running at Parkfield are available for viewing and downloading.