Low-Stress-Drop, Low-Magnitude Earthquake with Surface Faulting: The Imperial, California, Earthquake of March 4, 1966

Abstract

Right-lateral surface displacement reaching a maximum of 1 1/2 cm occurred over a 10-km section of the Imperial fault in association with a magnitude 3.6 earthquake on March 4, 1966, the smallest known earthquake yet associated with surface displacement. The displacement is documented by field observations of en echelon cracking in pavement and the offset of the white center line of Highway 80. The shallow depth of the earthquake source, the high excitation of waves in the top layer of sediments and of love waves of 8-15 sec periods, the distribution of aftershocks, and the agreement between the source moment as calculated from the observed faulting and from the amplitudes of love waves supports the association of the observed displacement with the March 4 earthquake.