Chapter B. The Loma Prieta, California, Earthquake of October 17, 1989 - Forecasts

Professional Paper 1550-B
Prepared in cooperation with the National Science Foundation



The magnitude (Mw) 6.9 Loma Prieta earthquake struck the San Francisco Bay region of central California at 5:04 p.m. P.d.t. on October 17, 1989, killing 62 people and generating billions of dollars in property damage. Scientists were not surprised by the occurrence of a destructive earthquake in this region and had, in fact, been attempting to forecast the location of the next large earthquake in the San Francisco Bay region for decades. This paper summarizes more than 20 scientifically based forecasts made before the 1989 Loma Prieta earthquake for a large earthquake that might occur in the Loma Prieta area. The forecasts geographically closest to the actual earthquake primarily consisted of right-lateral strike-slip motion on the San Andreas Fault northwest of San Juan Bautista. Several of the forecasts did encompass the magnitude of the actual earthquake, and at least one approximately encompassed the along-strike rupture length. The 1989 Loma Prieta earthquake differed from most of the forecasted events in two ways: (1) it occurred with considerable dip-slip in addition to strike-slip motion, and (2) it was much deeper than expected.
Publication type Report
Publication Subtype USGS Numbered Series
Title Chapter B. The Loma Prieta, California, Earthquake of October 17, 1989 - Forecasts
Series title Professional Paper
Series number 1550
Chapter B
DOI 10.3133/pp1550B
Edition -
Year Published 1998
Language ENGLISH
Publisher Geological Survey (U.S.)
Contributing office(s) Earthquake Hazards Program, Earthquake Science Center
Description p. B1-B28
Larger Work Type Report
Larger Work Subtype USGS Numbered Series
Larger Work Title The Loma Prieta, California, Earthquake of October 17, 1989: Earthquake Occurrence
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