Chronological Earthquake Index
Anza Gap Earthquake
TYPE OF FAULTING: right-lateral strike-slip
TIME: June 15, 1982 / 4:49 pm PDT
LOCATION: 33° 33.5' N, 116° 40' W about 3 km (2 miles) east of the town of Anza MAGNITUDE: ML4.8
DEPTH: 13.1 km
The name "Anza Gap Earthquake" is somewhat misleading; this earthquake did not actually take place along the so-called "Anza gap" -- a 40-km long segment of the San Jacinto fault zone that, when compared to the rest of that fault system over the last century, is deficient in slip -- proposed by Wayne Thatcher, James A. Hileman, and Thomas C. Hanks in 1975. Instead, the earthquake occurred on a separate fault, 3 km west of the surface trace of the San Jacinto fault, across from the center of the "Anza seismic gap".
Thatcher et al. reasoned, in 1980, that the Anza gap should be the site of a magnitude 6 to 6.5 earthquake in the near future, so the 1982 quake turned some heads, seismologically, but proved to be neither the "predicted" magnitude 6 quake, nor (as seemed more likely at the time) a foreshock to a larger event -- one like that which was postulated. Though it was felt over a wide area, it caused little damage, and would be more easily forgotten if not for its particular location.