Northridge earthquake rupture models based on the Global Positioning System measurements

Abstract

GPS data are used to study the rupture mechanism of the 1994 Northridge earthquake in southern California. In order to fit the geodetic data with a fault model whose primary fault patch is confined to a plane through the aftershocks, a secondary fault plane is required above the primary fault plane. The moment release of the secondary fault can be as large as 1.9 × 1018 N-m, 14% of the moment release of the primary fault. This results implies significant deformation in the shallow crust associated with the mainshock. The mainshock lies at the bottom of the aftershock zone, near which about 1-m slip is shown on the modeled fault surface. The maximum slip on the fault surface is about 2.2 m, located at 34.28°N, 118.55°W, and 12.4 km at depth. The seismic moment release estimate of 1.34 ± 0.15 × 1019 N-m on the main fault at the 95% confidence is consistent with the estimate from strong-motion studies.