A new study highlights how predominantly minority neighborhoods in Los Angeles — and especially those with Black populations — will be most affected in the aftermath of a large earthquake.
By Rebecca Owen, Science Writer (@beccapox)
Citation: Owen, R., 2024, Inequality persists after an earthquake’s impact, Temblor, http://doi.org/10.32858/temblor.335
It’s hard to avoid earthquakes if you live in Los Angeles. Underneath the sprawling city-scape, a tangle of potentially active faults makes residents worry when the next one might strike.
A powerful earthquake would likely affect nearly everyone, as well as the buildings and infrastructure. But houses can be rebuilt. Infrastructure can be repaired. Some neighborhoods and their inhabitants, however, would have a harder time rebounding from such a damaging event. Their community might be lost forever.
Catastrophe models can be used to assess the potential risks and losses that could affect a region when a natural hazard strikes. The output from these models allows insurers, city planners or other stakeholders to understand the potential severity of a catastrophic event as it relates to the built environment, the structures that a population inhabits. What catastrophe models don’t foretell is how that disaster impacts the people who live and work in those same structures — and how the fabric of a neighborhood could be irreparably harmed.
In a recent study presented at the 2023 fall meeting of the American Geophysical Union, Charles Huyck and Yajie Lee from ImageCat, a catastrophe modeling company, investigated the social vulnerability that traditional catastrophe models aren’t capturing. Using Los Angeles County as an example, Huyck, Lee and colleagues examined the financial impacts of a devastating earthquake by contrasting the average dollar loss per household with the number of people affected. By combining modeling tools with residential data, the researchers found an alarming disparity: Marginalized communities would be disproportionately affected in the wake of a large-scale disaster. This study is the first part of a longer conversation about creating more equitable earthquake mitigation practices in the future.
Connecting models to neighborhoods
Insurers use catastrophe modeling to assess the risk faced by individual structures, ranging from commercial and residential buildings to infrastructure. Annualized loss is based on the likelihood of more frequent events, rather than one large, infrequent event — like an earthquake — that could easily overwhelm residents collectively. “A community is vulnerable, or in more positive terms, less resilient, not only because of its economic status — there’s a compound effect of many other factors,” says Sahar Derakhshan, a professor of anthropology and geography at Cal Poly Pomona who was not involved in the study. Thus, while hazard, exposure and risk can be modeled, these modeling tools can’t yet accurately gauge the impact of how a community as a whole would be affected in the wake of a significant disaster.
Huyck and Lee wanted to reconcile these gaps in measuring community risk. They brought together census tract information with remote sensing and seismic modeling to examine the potential outcomes of thousands of worst-case earthquake scenarios in Los Angeles that would create probable maximum loss of property for insurers and risk managers.
To scale these scenarios, ImageCat developed a Global Economic Disruption Index (GEDI) — a scale of one through five — that can be used to assess how long recovery could take in an area affected by a disaster. On the low end of the GEDI scale, a level 1 event means a slight disruption, with services restored within a few hours to days. At the other end, a score of 5 means major disruptions that take years to recover from, like the aftermath of Hurricane Katrina in 2005, the 2011 Tōhoku earthquake and tsunami that resulted in a nuclear disaster in Japan, or the 2004 Indian Ocean earthquake and tsunami that devastated communities around the Indian Ocean basin. But smaller-scale disruptions than these catastrophes can still wreak havoc.
“Cities are like organisms,” says Huyck. “A mill town, for example: Everybody works at the mill. Well, what happens when you take out the mill in a flood?” What happens when power generation or lifeline systems go down? he says. Or a levy in New Orleans, “to borrow on a real example.”
Predicting the exact magnitude, timing and location of a future earthquake is scientifically impossible. But researchers can use geologic history and data from Earth’s movements to estimate the probability of where and when these future events may occur. Huyck, Lee and their colleagues examined the possible outcomes of a 475-year event and a 2,475-year event. For a 475-year scenario (which means they consider an earthquake that’s likely to occur approximately once every 475 years), though the probability may seem small in a year, “over a 50-year timeframe (a typical building design life), it escalates to 10%,” Lee says, “a significant figure given the potential large impact of such an event.”
The 2,475-year event has a 2% chance of occurring in a given year over that same 50-year period. “These concepts play a crucial role in shaping building codes for seismic safety design, conducting lifeline infrastructure performance assessments, and implementing many other risk mitigation measures,” Lee says.
Their findings showed that the 475-year event would be a GEDI level 4, meaning months of disruption before economic recovery. The 2,475-year event was a level 5. “Massive loss of cultural resources. A massive migration away from the area. Decimation of a historic community,” says Huyck. “It’s not only the whole probabilistic landscape, but also the impacts to the economic engine itself.”
Correlating income and ethnicity details about residents who would be most affected from these potential earthquakes revealed more alarming information. Huyck, Lee and colleagues examined four groups: the general population, Hispanic residents, low-income residents, and Black residents. Their findings showed that Black residents would be disproportionately harmed in the event of either scenario — and historically discriminatory housing practices like redlining might mean that property values are already lower and infrastructure could be neglected during rebuilding, more so than in surrounding areas.
Preparing for a more equitable future
“This type of examination of the social aspect [of a major earthquake] has not received as much attention as it should,” says Derakhshan. “In the end, we are looking at other people who are going to be suffering. These communities that are more vulnerable are usually the ones that didn’t have a voice.”
This study is a baby step, Lee explains — a move toward more use of models that apply probabilities to help understand how hazards become disasters that disrupt a whole community or neighborhood. This can lead to eventual mitigation efforts that are just and equitable for all the communities in a city as vast as Los Angeles, no matter the income level or ethnicity of its residents.
“If you want to enhance an under-resourced community’s resilience, there’s more to consider, not just property value,” Lee says. “These communities will have more need, especially in large, disastrous events.”
While this study is a step in the right direction, it is only the start. More research is needed to further investigate how the legacy of racism connects to the vulnerability and exposure to earthquake risk. FEMA, through its risk index, is starting to prioritize minority communities, Huyck says. With more comprehensive modeling, mitigation plans and policies can become more sophisticated and inclusive, he says. “It takes new invention to have the tools to be able to look at this problem in an adequate way.”
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