New Caltech research maps the underground shape of the Los Angeles Basin to show how soft sediments may amplify seismic shaking across Southern California, helping explain why some neighborhoods may experience stronger damage than others in a major earthquake.
Key facts
- The study used 273 temporary seismic sensors placed across the LA region for a month.
- The sensors were installed at roughly 1–2 kilometer intervals from Pasadena to Long Beach and from Santa Monica to Orange County.
- The map shows soft sediments are up to 10 kilometers deep beneath downtown Los Angeles.
- The research was led by Caltech graduate student Valeria Villa with seismologist Robert Clayton, professor of geophysics, emeritus.
- The paper appears in JGR Solid Earth on August 4 and is titled “Three-Dimensional Structure of the Los Angeles Basin and Its Underlying Moho.”
What does this mean for students, researchers and the region?
The study gives researchers a more detailed picture of how the LA Basin is built underground, which matters for simulating strong ground motion and understanding building safety. For students and scientists, it also shows how gravity measurements and dense sensor networks can be combined to study complex subsurface structures.
How did the team build the map?
The team installed hundreds of small seismic sensors throughout Los Angeles County and used measurements of gravity and seismic waves to infer the structure far below the surface. Those measurements were transformed into a 3D map of the basin, even though the basin itself scrambles the seismic signal.
Villa said that combining gravity with seismic data offered another way to identify buried interfaces that had been difficult to resolve before. The project also relied on participation from local homeowners and renters who hosted sensors in residential neighborhoods.
Why do deeper sediments matter?
Deeper sediments can produce longer-period shaking, which affects larger buildings more than shorter-period shaking. Clayton said basin variations control how damage is distributed from block to block, and that local soil differences can significantly affect the shaking of buildings and houses.
The study notes that soft sedimentary ground beneath the region can amplify seismic waves, as seen in simulations of a large earthquake on the San Andreas Fault. It also points to the 1933 Long Beach earthquake as an example of how an earthquake within the LA basin can be destructive.
What comes next in the research?
The team wants to map how the sediments connect with bedrock below, which would improve models of strong ground motions. It also hopes to learn more about the topmost kilometer of soil, where local variation is most consequential. Clayton said denser instrumentation, including community-sourced reporting such as “Did You Feel It,” could help build an even more detailed picture.
The geographical data from the study is publicly available on GitHub, and the research was funded by the National Science Foundation. Villa is supported by an NSF Graduate Research Fellowship.
