Earthquakes near Parkfield, California: Comparing the 1934 and 1966 sequences

Moderate-sized earthquakes (Richter magnitude ML 5 1/2) have occurred four times this century (1901, 1922, 1934, and 1966) on the San Andreas fault near Parkfield in central California. In many respects the June 1966 sequence was a remarkably detailed repetition of the June 1934 sequence, suggesting a recurring recognizable pattern of stress and fault zone behavior.