The Loma Prieta, California, Earthquake of October 17, 1989—Landslides

Central California, in the vicinity of San Francisco and Monterey Bays, has a history of fatal and damaging landslides, triggered by heavy rainfall, coastal and stream erosion, construction activity, and earthquakes. The great 1906 San Francisco earthquake (M_S=8.2-8.3) generated more than 10,000 landslides throughout an area of 32,000 km²; these landslides killed at least 11 people and caused substantial damage to buildings, roads, railroads, and other civil works. Smaller numbers of landslides, which caused more localized damage, have also been reported from at least 20 other earthquakes that have occurred in the San Francisco Bay-Monterey Bay region since 1838. Conditions that make this region particularly susceptible to landslides include steep and rugged topography, weak rock and soil materials, seasonally heavy rainfall, and active seismicity.

Given these conditions and history, it was no surprise that the 1989 Loma Prieta earthquake generated thousands of landslides throughout the region. Landslides caused one fatality and damaged at least 200 residences, numerous roads, and many other structures. Direct damage from landslides probably exceeded $30 million; additional, indirect economic losses were caused by long-term landslide blockage of two major highways and by delays in rebuilding brought about by concern over the potential long-term instability of some earthquake-damaged slopes.

This publication consists of the following articles:

• Synopsis, by David K. Keefer

• Regional distribution and characteristics of landslides generated by the earthquake, by David K. Keefer and Michael W. Manson

• Coastal-bluff failures in northern Monterey Bay induced by the earthquake, by Gary B. Griggs and Nathaniel Plant

• Landslide dams in Santa Cruz County, California, resulting from the earthquake, by Robert L. Schuster, Gerald F. Wieczorek, and David G. Hope II

• Large landslides near the San Andreas fault in the Summit Ridge area, Santa Cruz Mountains, California, by David K. Keefer, Gary B. Griggs, and Edwin L. Harp

• Origin of fractures triggered by the earthquake in the Summit Ridge and Skyland Ridge areas and their relation to landslides, by Edwin L. Harp

• Evaluation of coseismic ground cracking accompanying the earthquake: Trenching studies and case histories, by Jeffrey M. Nolan and Gerald E. Weber

• Analysis of earthquake-reactivated landslides in the epicentral region, central Santa Cruz Mountains, California, by William F. Cole, Dale R. Marcum, Patrick O. Shires, and Bruce R. Clark

  Plates

  Plate 1, Landslides and ground cracks generated by the 1989 Loma Prieta earthquake in the Santa Cruz Mountains and along adjacent sections of the California coast.

  Plate 2, Landslides and ground cracks generated by the 1989 Loma Prieta earthquake in the Laurel and Loma Prieta quadrangles.

  Plate 3, Large landslides, coseismic ground cracks, and geology in the summit ridge area, Santa Cruz Mountains, California.

  Plate 4 (A, B, C, and D), Landslide features and coseismic fissures in the Summit Ridge and Skyland areas generated by the 1989 Loma Prieta earthquake.

  Plate 5, Locations of sites severely damaged by ground cracking accompanying the 1989 Loma Prietta earthquake in the Summit Ridge area, Santa Cruz Mountains, California.

This publication is part of the set of four multi-chapter USGS Professional Papers on the Loma Prieta, California, Earthquake of October 17, 1989:

Professional Paper 1550, Earthquake Occurrence , Coordinators: William H. Bakun and William H. Prescott

Professional Paper 1551, Strong Ground Motion and Ground Failure, Coordinator: Thomas L. Holzer

Professional Paper 1552, Performance of the Built Environment, Coordinator, Thomas L. Holzer

Professional Paper 1553, Societal Response, Coordinator: Dennis S. Mileti