Ground fracturing at the southern end of Summit Ridge caused by October 17, 1989 Loma Prieta, California, earthquake sequence

The Loma Prieta earthquake of 17 October1 1989 was the first of three large earthquakes that occurred in California in less than 5 years. The main shock of the Loma Prieta earthquake was deep-seated, the rupture zones of the main shock did not reach the surface, and the earthquake produced enigmatic surface ruptures along the frontal faults of the Coast Range and in the epicentral area that were explained in several quite different ways. The Landers earthquake of 28 June 1992 was near surface and produced more than 80 km of spectacular surface rupture of many different kinematic expressions. Detailed study of fractures at Landers has provided a basis for re-evaluating our earlier work on fractures produced by the Loma Prieta earthquake. This paper is a description of some of the fractures produced by the Loma Prieta earthquake and a discussion of their causes.