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U.S. Geological Survey
Professional Papers 1550-A through 1550-F

Prepared in cooperation with the National Science Foundation

Earthquake Occurrence

Coordinated by William H. Bakun and William H. Prescott

The Loma Prieta Earthquake Professional Papers

The Loma Prieta Earthquake Professional Papers comprehensively document the magnitude 6.9 earthquake that shook the San Francisco and Monterey Bay regions on October 17, 1989. They contain almost 3000 pages written by 401 investigators of the earthquake. The investigations were funded by a special Congressional appropriation to the U.S. Geological Survey and National Science Foundation after the earthquake to improve understanding of both the complexity of earthquakes and how society can reduce losses in future earthquakes.

photo of the collapsed Cypress freeway viaduct taken from the ground beside the rubble of broken concrete and twisted steel

Professional Paper 1550 seeks to understand the M6.9 Loma Prieta earthquake itself. It examines how the fault that generated the earthquake ruptured, searches for and evaluates precursors that may have indicated an earthquake was coming, reviews forecasts of the earthquake, and describes the geology of the earthquake area and the crustal forces that affect this geology. Some significant findings were:

  • Slip during the earthquake occurred on 35 km of fault at depths ranging from 7 to 20 km. Maximum slip was approximately 2.3 m. The earthquake may not have released all of the strain stored in rocks next to the fault and indicates a potential for another damaging earthquake in the Santa Cruz Mountains in the near future may still exist.

  • The earthquake involved a large amount of uplift on a dipping fault plane. Pre-earthquake conventional wisdom was that large earthquakes in the Bay area occurred as horizontal displacements on predominantly vertical faults.

  • The fault segment that ruptured approximately coincided with a fault segment identified in 1988 as having a 30% probability of generating a M7 earthquake in the next 30 years. This was one of more than 20 relevant earthquake forecasts made in the 83 years before the earthquake.

  • Calculations show that the Loma Prieta earthquake changed stresses on nearby faults in the Bay area. In particular, the earthquake reduced stresses on the Hayward Fault which decreased the frequency of small earthquakes on it.

  • Geological and geophysical mapping indicate that, although the San Andreas Fault can be mapped as a through going fault in the epicentral region, the southwest dipping Loma Prieta rupture surface is a separate fault strand and one of several along this part of the San Andreas that may be capable of generating earthquakes.

This set of publications consists of the following Chapters:

These publications are part of a set of four multi-chapter USGS Professional Papers on the Loma Prieta, California, Earthquake of October 17, 1989. The other three consist of:

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

For questions about the content of these reports, contact Tom Holzer

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Maintained by: Michael Diggles
Created: July 17, 2006
Last modified: January 4, 2007 (mfd)