No matter what else is going on in the world, earthquakes are always relevant in California because they are a constant threat that can occur anywhere and at any time.

The topic has never been more timely than now. We recently marked the 50th anniversary of the San Fernando, or Sylmar, earthquake, which occurred on February 9, 1971. It may seem strange to say, but California is a much more earthquake-resilient place because of that event.

CISN ShakeMap depicting shaking intensities in the 1971 San Fernando M6.6 earthquake

Occurring just after 6 a.m., the San Fernando Earthquake was a wake-up call in every sense. Not the oft-referenced "big one," this magnitude 6.6 earthquake nonetheless caused 65 fatalities, 2,000 additional casualties, and damage of about $3.2 billion in today's dollars. It provided a glimpse of the huge potential for catastrophic losses of life and property in a larger quake. The type and extent of the damage prompted three pieces of safety legislation and initiated CGS programs that continue to protect Californians’ lives and property.

Damage done to hospitals in the San Fernando Valley gave rise to the Hospital Safety Act, which requires that all hospitals be able to function after large earthquakes. CGS reviews the geologic conditions and seismic hazards of older hospital retrofits and all new hospital buildings prior to construction to ensure they are not damaged by earthquake shaking, underlying faults, unstable soils, landslides and other geologic hazards. The law was based on the Field Act, instituted after the 1933 Long Beach Earthquake destroyed many schools. Similar site reviews for new schools are also conducted by CGS and just as for hospitals, every K-12 public school renovation or new building receives a careful geologic review.

Collapse of a stairwell at Olive View Medical Center, a new hospital dedicated in December 1970, just weeks before the earthquake. Photo by James Kahle, CDMG

The Alquist-Priolo Earthquake Fault Zoning Act was another response to the San Fernando Earthquake. It recognized by the extensive damage done by surface fault rupture -- that is, a trace of an underground fault breaking the surface and causing the ground to deform. CGS establishes Earthquake Zones of Required Investigation. Within those zones, local authorities must require appropriate geologic investigations prior to new construction to ensure that buildings aren’t placed atop surface faults.  Later legislation also added areas prone to liquefaction (the ground temporarily losing its ability to support structures due to high shaking) and earthquake-induced landslides. California residents can determine whether their homes are in an Alquist-Priolo Earthquake Fault Zone or a Seismic Hazard Zone by visiting the California Earthquake Hazards Zone Application (EQ Zapp).

The Strong Motion Instrumentation Program (SMIP) was created to help seismologists and engineers better understand the effects of ground motion and how structures respond to earthquake shaking. This CGS program operates a network of thousands of seismometers and accelerometers around the state –on dams, bridges, high-rises, and civic buildings, among other structures, and in the ground.  The data SMIP instruments collect helps strengthen California's building codes and enables engineers to design structures that can better withstand earthquake impacts. The data can help guide first responders to the hardest-hit areas after a quake, and many SMIP instruments have been upgraded to collect and transmit near real-time data for California’s earthquake early warning network, ShakeAlert.

These programs have made California safer in subsequent earthquakes. However, if an earthquake is large enough and close enough to an urban area, there will be casualties and fatalities; serious damage to buildings and infrastructure; impacts to public services, communications, transportation -- society as a whole. The impact of such an event in normal times is frightening: the impact on the state given current events is hard to imagine.

Advances in earthquake preparedness and resilience will come from a greater understanding of the effects of seismic energy as it enters buildings and infrastructure and dissipates energy in the structure.  Advancing technologies can now aid with health monitoring of infrastructure before, during and after a seismic event; data that can better direct emergency services; hasten the return to service of buildings, bridges and other essential infrastructure; and lessen economic losses. In addition, CGS continues to upgrade seismic networks and use cutting-edge science to improve earthquake zone maps essential for the seismic resilience of California.

Every Californian has an important role in earthquake safety. Despite all the progress California has made toward earthquake resilience thanks to the efforts of CGS, SCEC, CalOES, and other agencies, having the essentials you’ll need in the event of an earthquake, landslide, wildfire, or other geologic hazard is vital. Every Californian needs a plan for reconnecting with family members without cell phones; food, water and first aid supplies; a family meeting place; and preparations for housing should circumstances require.

Most people will survive even the largest earthquakes. The most important question to consider is, what will you do after you survive?

About the Author

Steve Bohlen became Acting State Geologist and head of the California Geological Survey on June 1, 2020. He re-joins the Department of Conservation (where he served as State Oil and Gas Supervisor from 2014-2015) from the Lawrence Livermore National Laboratory, where he led the Energy and Homeland Security Program. A graduate of the Dartmouth College, Steve earned a Ph.D. in geochemistry from The University of Michigan in 1979. Following a postdoctoral fellowship at UCLA, he became a tenured professor at Stony Brook University in New York​. From 1995 through 2000, Steve was Associate Chief Geologist for Science at the US Geological Survey.