Parkville, California

Parkville, California is a small town that lies on the San Andreas Fault. Six successive magnitude 6 earthquakes occurred on the fault at unusually regular intervals, between 21 and 24 years apart, beginning in the mid-nineteenth century, with the most recent occurring in 1966.

Geologists who hoped to study what happens before a quake, and in particular any signs that might enable them to predict future earthquakes, installed an elaborate array of seismometers and other instruments in and around Parkville starting in 1985.

As of mid-2002, the expected significant earthquake had not occurred. Researchers have been asking why not. A possible explanation for part of the delay is that earthquakes near Coalinga, California in 1983 reduced the stress on the Parkville section of the San Andreas fault. This stress reduction is estimated to have delayed the "next" Parkville quake by about ten years. Seismicity at Parkville increased in the late 1990s and early 2000s, suggesting that this section of the San Andreas fault may be returning to its previous cycle.