Crustal deformation across and beyond the Los Angeles basin from geodetic measurements

TLDR

We combine six years of GPS data with two decades of trilateration and a century of triangulation, taped‑distance, and astronomic azimuth measurements to derive 66 interseismic station velocities in the greater Los Angeles region and then interpolate these velocities to construct a regional strain‑rate map beyond the basin. The results confirm the 1995 California Earthquake Probabilities model and reveal significant north‑south convergence (~0.22 µstrain yr⁻¹) and east‑west extension (~0.17 µstrain yr⁻¹) along the southern San Gabriel Mountains, show that deformation around the Big Bend of the San Andreas fault cannot be explained solely by wrench motion and may involve NW‑SE extension or left‑lateral faulting on an oblique blind thrust, report low strain rates along the Elsinore and Newport‑Inglewood faults, and note decreasing north‑south compression from the Raymond Hill to Santa Monica fault with little east‑west extension.

Abstract

We combine 6 years of Global Positioning System (GPS) data with 20 years of trilateration data and a century of triangulation, taped distance, and astronomic azimuth measurements to derive 66 interseismic station velocities in the greater Los Angeles region. We interpolate the velocities to construct a regional strain rate map beyond the Los Angeles basin. Our results generally agree with the model proposed by the Working Group on California Earthquake Probabilities in 1995. Important regional findings of this study are as follows: (1) There is a significant N‐S convergence and E‐W extension, about 0.22 and 0.17 ± 0.05/μstrain/yr, respectively, for the two components, along the southern frontal fault system of the San Gabriel Mountains. (2) The crustal deformation around the Big Bend of the San Andreas fault (SAF) cannot be explained solely by wrench‐style motion across the SAF. Remaining motion could be part of a NW‐SE extension which is the response to NE‐SW compression in the central Transverse Ranges region. Alternatively, it could be caused by left‐lateral faulting on an oblique blind thrust beneath the San Gabriel Mountains. (3) Low strain rates are found along the Elsinore fault and Newport‐Inglewood fault. (4) North‐south compression decreases from the Raymond Hill fault westward to the Santa Monica fault. There is little east‐west extension along this fault system.