Who is most vulnerable during a major Northern California earthquake?

A study shows that the most socioeconomically vulnerable communities in California are also most vulnerable to earthquakes; they’re likely to experience the greatest damage.

By Olivia Box (@oliviafaybox)

Citation: Box, O., 2021, Who is most vulnerable during a major Northern California earthquake?, Temblor, http://doi.org/10.32858/temblor.163

Most risk analysis focuses on the cascading effects of an earthquake such as landslides, fire or building damage. A recent analysis took this assessment a step further and examined how different communities would be affected by a big earthquake in the Bay Area. The team found that the region’s most socioeconomically vulnerable communities would experience the most damage, thus perpetuating a cycle of poverty, displacement and inequity. All hope is not lost, however: The study, released by the U.S. Geological Survey (USGS), emphasizes that policy and planning measures before an earthquake can help mitigate high rates of population displacement and create a more equitable path through a natural disaster.

Bay Area quake risk

According to USGS assessments, there is a 72% chance that the Bay Area will experience a large-magnitude earthquake before 2043, whether on the San Andreas Fault, the Hayward Fault or another one. Scientists consider the Hayward Fault, running through the eastern Bay Area from San Jose north through Berkeley, to be a ticking time bomb. The last large-magnitude earthquake on the fault was in 1868. When the next earthquake comes, the effects of the shock won’t be felt equally across the Bay Area.

HayWired scenario

A magnitude-7.0 earthquake on the Hayward Fault has the potential to damage up to 1 million homes and cause $74 billion in property damage, according to the new study, released as part of the USGS-led HayWired Scenario project.

Through the HayWired Scenario, scientists from USGS and partners work to understand the potential effects of an earthquake on the Hayward Fault and how to best prepare the region for such a quake. It is a long-term study that started with forecasting the chance of an earthquake, then looked at engineering implications of such a quake and has now moved onto analyzing the potential damage to various communities.

Map of San Francisco Bay Area with faults as red lines
The Hayward Fault in California cuts through several highly populated cities.


As part of the HayWired Scenario project, Laurie Johnson, a disaster recovery and risk management consultant and researcher who works independently and for the California Earthquake Authority, led a community vulnerability study, which she presented at the Northern California Earthquake Hazards Workshop in February. Johnson has worked on disaster relief projects from Hurricane Katrina to the 2011 earthquake in New Zealand. After these disasters, she says, “there were a lot of areas that were heavily damaged, and the government ended up buying people out. People were displaced from their homes. This has been an issue I want to bring to the Bay Area: Many people live here, and a ton of our workers will be displaced.”

black and white photo of destroyed buildings
A historical photo of the 1906 magnitude-7.9 earthquake in San Francisco. Credit Chadwick, H. D., National Archives and Recordings Administration, public domain


Vulnerable communities

The study defined communities at risk as areas where community elements, such as buildings, water quality and public transportation, could be damaged for months or years after an earthquake. To determine the communities that would be most affected in the Bay Area, Johnson and her team integrated the property damage analysis from the HayWired scenario with U.S. Census data and a community vulnerability index from the Association of Bay Area Governments. They then came up with a list of factors that identify neighborhoods as more vulnerable to the short and long-term effects of a disaster.

Factors included whether households made below the median income, had school-age children, disabled residents or non-English speakers, or had a head of household younger than 34 years old, and whether an area had a high homeless population.

Johnson and her team found that Alameda and Contra Costa counties are likely to experience the most building damage, and 350,000 residents of those counties would be considered most vulnerable in preparing for and dealing with the effects of an earthquake. The most vulnerable residents, according to the study, scored high on the list of factors, meaning they meet more than one characteristic on the list. This could mean a resident making below the area’s median income, who is a non-English speaker and has school-age children at home.

After an earthquake, these vulnerable residents might not be able to repair their homes or purchase a new home in the same area. Residents then leave voluntarily or are forced to leave due to the damages. “We think of displacement as happening all at once, and we just count people who are in the evacuation shelters. But displacement happens over time,” Johnson says.

Mobility and socioeconomic status are two driving factors in why a person may leave after a disaster — whether it be immediately or in the few years afterward.

A young renter, for example, is likely more mobile and may not be as tied to the community. Low-income homeowners, meanwhile, may be forced to leave due to lack of jobs or inability to pay for housing damages. The new housing built after an earthquake may also be more expensive, which may force people to move elsewhere.

Displacement can cause long-term social and economic consequences for a city. Just look at the ghost towns that were left after the 1994 Northridge earthquake in Los Angeles, Johnson says. “People didn’t want to live in those neighborhoods because the damaged buildings attracted crime and a negative reputation. So even more people left and the city had to intervene.”

Photo of iconic San Francisco homes with cityscape in background.
A view of San Francisco. Some older homes are elevated off the foundation, which puts them at higher risk of damage during an earthquake. Credit: King of Hearts (CC BYSA 3.0)


The effects of earthquakes extend beyond the aftershock

The study highlighted three long-term challenges for cities in preventing displacement: gathering financial resources, repairing damage and enlisting significant government aid.

Berkeley, Oakland and the city of San Francisco have been taking steps to upgrade publicly and privately owned housing that might be vulnerable to an earthquake, such as developing the Brace and Bolt program in Oakland, which incentivizes homeowners to retrofit their homes by fixing them to their foundations. This can make them better able to withstand a large-magnitude earthquake.

Wealthier cities have had more success implementing these kinds of programs because they have a stronger tax base, Johnson says. These home improvements need to be tracked better, though, she says, as building upgrades are not consistent. A neighborhood can be a mix of homes that have been retrofitted and ones that have not, which makes the entire neighborhood vulnerable. “We need to do this in a spatially consistent way,” she says. “It’s like herd immunity — one house fixed won’t inoculate the herd.”

But preparedness goes beyond just fixing housing. The study puts forward several other policy suggestions such as building more housing for low-income residents, planning for long-term recovery and educating people about their insurance and housing options in advance.

Preparedness requires good communication, says Mark Benthien, director for communication, education and outreach for the Southern California Earthquake Center, who was not involved in the study. Programs like the Earthquake Country Alliance and Listos California, which both focus on building resiliency before an earthquake, are helpful in that these programs reach the most-vulnerable residents, he says, including low income residents and underserved minorities.

The key is to talk with a community and not at them, says Benthien. “Involve the actual community leaders, which may not be the elected officials.” Earthquakes can disrupt a community’s identity, he says: Getting people to talk about what’s important to them ahead of time allows them to plan how to sustain what they like, instead of just preventing the damage.