Don's Home Places California Bay Area Earthquakes Loma Prieta Earthquake

The highest concentration of fatalities, 42, occurred in the collapse of the Cypress Street Viaduct on the Nimitz Freeway (Interstate 880), where a double-decker portion of the freeway collapsed, crushing the cars on the lower deck.


The 1989 Loma Prieta earthquake was the largest earthquake to occur on the San Andreas Fault since the great 1906 San Francisco earthquake. It ruptured the southernmost 40 km of the 1906 break.
Magnitude: 6.9 MW, 7.1 MS , 6.7 ML
The epicenter of the quake was in Forest of Nisene Marks State Park in the Santa Cruz Mountains north of Aptos and approximately 10 miles northeast of Santa Cruz.
It occurred at 5:04 Pacific time on October 17, 1989 at the start of the 3rd world sieries game from Candlestick Park. It lasted for 15 seconds.

Sixty-three deaths were directly caused by the earthquake; six further deaths were ruled to be caused indirectly.

There was more than $7 billion in property damage.
The damage San Francisco's Marina district, 60 miles from the epicenter, was due to the amplification of the earthquake's Seismic waves reflecting from the Moho discontinuities. (The "Moho" is short for the Mohorovicic discontinuity, the boundary between the earth's crust and mantle (about 15 miles deep), and is named for the Croatian scientist who discovered it.)
See: How Distance and Directivity Affect Shaking Intensity

Information and Links at
Information at the USGS

Photographs at USGS

Description at John Martin Structural Engineers

Many homes in the San Francisco's Marina District were destroyed or damaged. The area was built on landfill and thus the ground became unstable. (See Liquification)
Thirty-five of the buildings were eventually torn down here.

One section of the upper deck of the Bay Bridge fell.

Isoseismals based on intensity estimates.

Source: USGS
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last updated 20 June 2009