1989 Loma Prieta Earthquake: The World Series Quake in California

The Loma Prieta earthquake struck the San Francisco Bay Area and the Monterey Bay region at 5:04 pm on 17 October 1989. With a magnitude of 6.9, it killed 63 people and caused billions of dollars of damage. Because it hit just before a World Series game between two Bay Area teams, millions of television viewers across the United States witnessed its first moments live.

The earthquake

The earthquake began about 18 kilometers (11 miles) beneath the Santa Cruz Mountains, near Loma Prieta peak, roughly 16 kilometers northeast of the city of Santa Cruz. It ruptured a section of the San Andreas fault zone about 40 kilometers long. Strong shaking lasted for roughly 10 to 15 seconds.

Damage was heaviest not only near the epicenter but also around San Francisco Bay, about 100 kilometers away. There, areas built on soft mud and artificial landfill amplified the shaking. Some filled ground lost its strength in a process called liquefaction, in which water-soaked sand behaves like a liquid.

The World Series

At Candlestick Park in San Francisco, around 62,000 fans were waiting for Game 3 of the World Series between the San Francisco Giants and the Oakland Athletics. The ABC television broadcast was under way when the picture broke up as the stadium shook. The game was postponed, and the stadium was evacuated without serious injury.

The series resumed on 27 October, and Oakland completed a four-game sweep. Many people had left work early to watch the game, so traffic on Bay Area roads was lighter than in a normal rush hour, which probably reduced the death toll.

Collapse of the Cypress Viaduct and the Bay Bridge

The worst single disaster occurred in Oakland. The Cypress Street Viaduct, a double-deck section of the Nimitz Freeway (Interstate 880) built in the 1950s on soft ground, collapsed along more than a kilometer of its length. The upper deck fell onto the lower one, crushing cars, and 42 people were killed. Local residents and workers joined emergency crews in dangerous rescue efforts.

On the San Francisco–Oakland Bay Bridge, a 50-foot (15 m) section of the upper deck of the eastern span fell onto the lower deck. One person died. The bridge, a vital commuter link, was closed for a month and reopened on 18 November 1989.

Damage elsewhere

In San Francisco’s Marina District, built partly on landfill that included debris from the 1906 earthquake, buildings sagged and collapsed and a broken gas main fed a large fire. The city’s fireboat and volunteers pumping water from the bay helped bring it under control. In Santa Cruz, the historic Pacific Garden Mall was badly damaged and several people died, and towns such as Watsonville and Hollister also suffered heavy losses.

In all, the earthquake injured about 3,800 people and damaged or destroyed thousands of homes and businesses. Estimates of total damage range from about $6 billion to $10 billion.

Response and science

Emergency services, the American Red Cross and thousands of volunteers worked through the night, often without electricity, as power was cut to much of San Francisco. President George H. W. Bush visited the area, and Congress approved several billion dollars in emergency relief. Thousands of people were left temporarily homeless, especially in Santa Cruz County and in older neighborhoods of San Francisco and Oakland.

For seismologists, Loma Prieta was one of the best-recorded large earthquakes of its time. Instruments captured how soft bay mud amplified shaking far from the epicenter, findings that improved ground-motion maps and building codes. The quake also struck a segment of the fault that scientists had identified in the 1980s as likely to rupture, which encouraged further work on long-term earthquake forecasting for the Bay Area.

Rebuilding and retrofitting

The Loma Prieta earthquake exposed the weakness of older concrete freeways and bridges. The California Department of Transportation (Caltrans) greatly expanded its seismic retrofit program, strengthening hundreds of bridges with steel jackets and other measures. A rerouted section of Interstate 880 replaced the Cypress Viaduct and opened in 1997.

San Francisco took the opportunity to demolish the damaged Embarcadero Freeway in 1991, opening up its waterfront. The eastern span of the Bay Bridge was eventually replaced by a new self-anchored suspension bridge that opened in September 2013. Lessons from Loma Prieta, and from the Northridge earthquake of 1994, shaped building codes across California.

Timeline

• 1989, 17 October, 5:04 pm: The magnitude 6.9 earthquake strikes.
• 1989, 17 October, evening: The Cypress Viaduct collapses and fire breaks out in the Marina District.
• 1989, 27 October: The World Series resumes in San Francisco.
• 1989, 18 November: The Bay Bridge reopens to traffic.
• 1991, February: Demolition of the Embarcadero Freeway begins.
• 1997, July: The rebuilt Interstate 880 route opens in Oakland.
• 2013, 2 September: The new eastern span of the Bay Bridge opens.

Why it matters

The Loma Prieta earthquake was a warning of what a larger quake could do to a modern American metropolitan region. It showed the dangers of soft ground and older concrete structures and led to billions of dollars of investment in safer bridges, freeways and buildings across California.