How Los Angeles’ Geology Can Intensify an Earthquake

On October 15, millions of people will participate in the Great California ShakeOut. Chukwuebuka Nweke, an assistant professor in USC Viterbi's Sonny Astani Department of Civil and Environmental Engineering, studies how local and regional geology affects earthquake ground motion. His research combines recorded data, empirical analysis and physics-based simulations to improve seismic hazard estimates in Southern California.

We cannot currently predict when and where the next major earthquake will occur. While we can estimate the probability of an earthquake occurring on or near a fault over a specified period, no accepted method can identify its precise time and location in advance.

However, with more extensive sensor networks, greater access to recorded data and advances in physics-based simulation, we can characterize with increasing precision how seismic energy may propagate through a region and how the resulting ground motion may vary among locations.

My research group is currently developing ground motion models and evaluating physics-based simulations that characterize variations in ground-shaking amplification across the Los Angeles Basin. Sedimentary basins can amplify seismic waves, and our simulations indicate where amplification is likely to occur and estimate its intensity.

The rapid influx of data in recent years has allowed us to achieve ever greater precision. Because the simulations necessarily simplify geological complexity, their assumptions must be tested against recorded observations and calibrated to the region being modeled.

In recent work, we found that inadequate regional calibration could alter predicted ground-motion estimates by approximately 20 to 30 percent, affecting the assessment of buildings and networked infrastructure such as power grids and pipelines. More reliable models can strengthen seismic hazard assessments and inform building codes, infrastructure design and retrofit priorities.

It's important to recognize that the impacts of an earthquake are as much about the geology of the region as the fault itself. A fault releases seismic energy, but the hazard at a particular site also depends on how that energy interacts with the surrounding geology. When seismic waves pass through deep deposits of relatively soft sediment, the basin can resonate at particular frequencies, increasing ground motion at the surface.

The 1985 Michoacán earthquake was a case in point. Although the earthquake occurred approximately 380 kilometers from Mexico City, parts of the city experienced severe shaking. Much of Mexico City stands on a former lakebed, and the deep, soft sediments beneath it resonated with the incoming waves, magnifying their effects far from the source.

Southern California contains several such basins - broad depressions in the underlying bedrock filled with layers of sediment - including the Los Angeles, San Fernando and San Gabriel basins. The Los Angeles Basin is especially consequential because its potential to amplify seismic waves coincides with dense development and infrastructure of national and international importance, including LAX, the ports of Los Angeles and Long Beach, and major transportation and utility networks.

The ShakeOut rehearses how people should respond when shaking begins. Earthquake engineering examines the conditions that will shape that shaking: how seismic energy could travel through Southern California, where ground motion may be amplified by the geology and which structures and infrastructure systems would be exposed. We can't determine when the next major earthquake will occur, but we can increasingly anticipate its effects and take steps to reduce the damage.

Published on October 13th, 2026

Last updated on October 13th, 2026