30 Years After Loma Prieta, CGS Continues to Ensure Safety of California

CGS SMIP crew installing seismic instruments on the Oakland-Bay Bridge.

As the 30th anniversary of the devastating Loma Prieta Earthquake approaches, it’s time to take stock of California’s preparedness. The California Geological Survey (CGS) has a large role to play in that area:

  • Since that magnitude 6.9 earthquake, which occurred on October 17, 1989, CGS began the Seismic Hazards Mapping Program to create maps and zones requiring local authorities to ensure new construction accounts for certain earthquake hazards.
  • CGS also reviews geotechnical studies for schools and hospitals to protect some of our most vulnerable residents.
  • And, through its California Strong Motion Instrumentation Program (CSMIP), CGS places instruments on buildings, bridges, dams, other structures, and on and below ground surface to collect data about how ground and structures respond to strong shaking.

After a large earthquake, the information gathered by CSMIP is processed and disseminated to seismologists, engineers, building officials, local governments, and emergency response personnel throughout the state. The data is used to develop recommended changes to seismic provisions of building codes, to assist local governments in their general plan process, and to create a “ShakeMap” within minutes of the quake to show emergency responders where the heaviest shaking occurred.

All those services are important, of course, but the influence on building codes and future construction practices is key. The state’s modern infrastructure is built with surviving earthquake shaking in mind. As the Loma Prieta Earthquake showed — 63 dead, 3,737 injured, $6 billion in property damage — there is still much to learn. Large earthquakes are infrequent but inevitable in California.

NBC News file photo – an Oakland freeway pancakes during the Loma Prieta earthquake.

At the time of the Loma Prieta quake, CSMIP had 450 active stations around the state, of which 96 recorded data. The density of instruments has improved dramatically over the years. Following the July 5 magnitude 7.1 Ridgecrest Earthquake, 366 of CSMIP’s 1,350 stations provided strong-motion data. Over the Fourth of July weekend and the following weeks, the dedicated CSMIP staff processed more than 4,100 records from the 38 earthquakes of magnitude 4.5 or greater associated with the Ridgecrest sequence.

Photo library CGS checking an instrument on the Oakland end of the Bay Bridge
CGS personnel checking a seismic instrument.

Not only is more data coming in to help ensure the resiliency of California’s infrastructure, it’s coming in faster.

After the Loma Prieta quake, CSMIP staff had to go to each station to fetch film records of the shaking from the instruments, develop the film, and scan and digitize the film. The first results were made available to scientists and engineers a month after the earthquake. Following the Ridgecrest earthquakes, data started coming in within a few minutes, transmitted directly from the instruments in the field to the CSMIP strong-motion processing center.

Among other things, CSMIP data prompted Caltrans to immediately check the structural integrity of a bridge 13½ miles from the epicenter of the magnitude 7.1 temblor.

CSMIP is also an important part of California’s nascent earthquake early warning system. The California Integrated Seismic Networks (CISN) plans to have more than 1,100 stations around the state providing real-time data that will result in a “ShakeAlert,” giving people precious seconds to prepare for strong shaking. CSMIP, as a partner of the CISN, has converted 101 stations to do both their traditional job – collecting data to improve engineering practices – and provide immediate data for early warning. The program will upgrade or install new instruments at another 32 stations by June 2021.

When it comes to protecting the lives and properties of Californians, there’s no such thing as too much information.

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