Are we over due for another – October 17, 1989, Loma Prieta


On October 17, 1989, at 5:04:15 p.m. (P.d.t.), a magnitude 6.9 (moment magnitude; surface-wave magnitude, 7.1) earthquake severely shook the San Francisco and Monterey Bay regions. The epicenter was located at 37.04° N. latitude, 121.88° W. longitude near Loma Prieta peak in the Santa Cruz Mountains, approximately 14 km (9 mi) northeast of Santa Cruz and 96 km (60 mi) south-southeast of San Francisco. The earthquake occurred when the crustal rocks comprising the Pacific and North American Plates abruptly slipped as much as 2 meters (7 ft) along their common boundary-the San Andreas fault system. The rupture initiated at a depth of 18 km (11 mi) and extended 35 km (22 mi) along the fault, but it did not break the surface of the Earth .

Just minutes before the start of the third game of the 1989 World Series in San Francisco, a magnitude 6.9 earthquake rocked Northern California from Monterey to San Francisco. Centered near Loma Prieta peak in the Santa Cruz Mountains south of San Jose, the quake killed at least 63 people and hospitalized another 350. It destroyed a freeway viaduct in Oakland, dropped a span of the Bay Bridge, collapsed historic buildings in Santa Cruz and apartment buildings in the Marina District in San Francisco, severed communications, and caused an estimated $6 to $10 billion in property loss. It was the largest temblor to jolt the Bay Area since the Great San Francisco Earthquake of 1906 (magnitude 7.9).

Although the Loma Prieta earthquake struck on the outskirts of the region, it exposed the vulnerability of the Bay Area to future earthquakes—a vulnerability that was reemphasized on August 24, 2014, when a magnitude 6.0 earthquake occurred near Napa, California, about 30 miles north-northeast of San Francisco. At least 200 people were treated for quake-related injuries, and initial economic losses are estimated to be at minimum $362 million. Some future earthquakes will certainly be larger and closer to the Bay Area’s urban core than the 1989 and 2014 earthquakes.

“The Working Group on California Earthquake Probabilities estimated after the 1989 Loma Prieta earthquake that the probability of a magnitude 7 earthquake in the next 30 years in the San Francisco Bay region was 67 percent.” (U.S.G.S. Circular 1053) USGS

California’s in an exceptional earthquake drought. When will it end?

“The greater San Francisco Bay Area has been particularly quiet. Since the great 1906 earthquake destroyed much of San Francisco, there have been only three earthquakes of magnitude 6 or greater. But in the 75 years before that catastrophe, there were 14, according to geophysicist Ross Stein.”

California’s Current Earthquake Hiatus is an Unlikely Pause

“There have been no major ground rupturing earthquakes along California’s three highest slip rate faults in the past 100 years. A new study published in Seismological Research Letters concludes that this current “hiatus” has no precedent in the past 1000 years.”

About Kevin

Councilmember - City of Oakley, Manager of Mainframe Operations and Optimization – USS-POSCO INDUSTRIES, Co-Founder and Board Member - Friends of Oakley A Community Foundation, Commissioner - Contra Costa Transportation Authority, Board Member - Tri Delta Transit, Transplan, San Joaquin Joint Powers Authority and RD 2137, Advisory Board – Opportunity Junction
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