Los Angeles Basin map shows deep sediments that could amplify earthquake shaking
In computer simulations of the Big One—a large-magnitude earthquake that may occur along the San Andreas Fault in California—seismic waves ripple from the epicenter of a magnitude 7.8 earthquake near the Salton Sea into the Los Angeles Basin.
Researchers have mapped the deep sediments beneath Los Angeles that could intensify earthquake shaking. In computer simulations of a major quake along the San Andreas Fault, seismic waves ripple from the epicenter into the Los Angeles Basin, causing ground shaking for minutes. The basin's soft sediments amplify seismic waves, resulting in prolonged shaking that can be felt for longer periods and affect larger buildings more severely.
A Caltech study installed 273 temporary seismic stations throughout Los Angeles County to map the basin's underground structure. The map shows that soft sediments can reach up to 10 kilometers (6 miles) deep beneath downtown Los Angeles, while other regions sit atop shallower sediments. Variations in the basin's underground structure impact building damage distribution, with deeper sediments causing longer-period shaking that affects larger buildings more significantly.
The study, led by Caltech graduate student Valeria Villa, involved installing sensors at intervals of 1–2 kilometers (0.6–1.2 miles) and measuring seismic waves and gravity to create a 3D map of the region's underground structure. This detailed information can help improve building safety assessments and tailor local ground-motion models.
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