done to transportation arteries. The Bay Bridge,
which links San Francisco to Oakland, sustained a
steel truss failure, causing two fifty-foot spans of the
upper deck to collapse onto the lower deck. Two in-
terstate highways, Highway 280 and Highway 880
(also known as the Nimitz Freeway), suffered major
failures in their reinforced concrete structure. The
upper deck of the freeway collapsed at the Cypress
Street viaduct, in the western suburbs of Oakland.
Forty-two people died in the collapse, crushed by
tons of concrete, burned by gas tank explosions, or
killed when their vehicles were thrown from the
pitching roadway. Casualties continued for some
time after the initial event. Thirty minutes after the
collapse, a twenty-three-year-old woman died when
she failed to notice the gap in the upper deck of the
Bay Bridge and drove over the precipice. More than
seven hours after the earthquake, a driver was killed
when he hit three horses running loose on the Santa
Cruz freeway, and a civilian was gunned down as he
was directing traffic in San Francisco.
Liquefaction Most of the loss of life caused by the
earthquake was associated with the failure of human-
made structures, much of which was the result of a
geologic process called liquefaction. Underneath
the area where the earthquake struck sit loosely
compacted alluvial deposits in riverbeds and soft
mud around the bay. There is also a considerable
amount of artificial fill, used by builders to extend
the developable portion of the
Bay Area. Although the 1906 San
Francisco earthquake had already
demonstrated that these soils are
not suited to withstand ground
motion triggered by an earthquake,
the practice of using fill contin-
ued. Moreover, the Bay Area has a
very shallow water table, which
saturates the underground mate-
rials. Soft mud, alluvial deposits,
and loosely compacted fill amplify
the shaking of an earthquake, and,
when combined with a shallow
water table, they can produce se-
vere ground failure. During lique-
faction, the strength of the soils
decreases and the ability of these
materials to support bridge and
building foundations is so dimin-
ished that buildings tilt, freeway overpasses collapse,
and gas pipelines and water mains break.
Geologic studies were conducted after the Loma
Prieta earthquake to examine prehistoric earth-
quakes, not only on the San Andreas Fault but also
on the Hayward and Calavera faults. Integrating the
information gained in these studies with its recent
observations, the U.S. Geological Survey (USGS)
reported in 1990 that there was a 60 percent prob-
ability that one or more destructive earthquakes
(magnitude 7.0 or larger) would occur in the San
Francisco Bay Area between 1990 and 2020. Other
studies undertaken by the California Division of
Mines and Geology and the USGS have led to signifi-
cant changes in building codes related to the design
and construction of bridges, highways, and build-
ings. At the federal level, the Federal Response Plan
was created to better organize the activation, mobili-
zation, and deployment of personnel and resources
and the assessment of damages.Impact The highly televised earthquake was an in-
stant reminder of the danger of living along a tec-
tonic plate boundary, and it stimulated much re-
search to assess both the probability and the possible
impact of more major earthquakes striking the San
Francisco Bay Area. Scientists thus attempted to pro-
vide people with better tools to build a more secure
life on unstable land.600 Loma Prieta earthquake The Eighties in America
A section of the San Francisco-Oakland Bay Bridge that failed during the Loma Prieta
earthquake. The bridge had been scheduled to be reinforced the following week.(NOAA)