Three‐Dimensional Structure of the Los Angeles Basin and Its Underlying Moho

Abstract

The sedimentary basin beneath the city of Los Angeles and surrounding area intensifies seismic ground motions and prolongs the duration of shaking experienced by major population centers and infrastructure in Southern California. Characterizing the basin's shape, which in this case, has been altered over the course of its complex tectonic evolution, is necessary for improving predictions of the strong motions of large earthquakes such as the potential Mw 8 on the southern San Andreas fault. Using a data set acquired in Fall 2022, when 273 seismic nodes were installed in the Los Angeles Basin (LAB), we applied a novel algorithm to identify the P‐to‐S conversion and related phases from the sediment‐basement interface, intrasedimentary layers, and the Moho discontinuity in receiver functions. The survey included two linear arrays and a distributed set of shotgun stations, a configuration that typically challenges receiver function analysis due to phase incoherency among sparsely spaced stations. We addressed this limitation by integrating gravity measurements, allowing us to jointly interpret the multi‐layer crustal structure. Our results reveal a narrow, oblong basin with a maximum depth approaching 10 km. Assuming isostatic equilibrium, we find that the Moho is uplifted beneath the basin by up to 45% when compared to the surrounding crust.