Static and dynamic study of earthquake source mechanism: San Fernando Earthquake

The source mechanism of the San Fernando earthquake on February 9, 1971, was studied by utilizing seismic body waves, surface waves, and the static displacement and strain fields. For computing the static fields due to a fault model with arbitrary dip and slip directions, Maruyama's equations are integrated numerically. Very strong asymmetries in displacement fields and complicated surface strain patterns are produced by the dip of the fault plane and inclination of the dislocation vector. The joint interpretation of the body and surface waves, near-field displacement, and far-field strain fields completely define all important source parameters. The mechanism of the San Fernando earthquake is a reverse fault (strike N70°W, dip 52°NE, slip 225°) with dimensions of 14 by 14 km. The average dislocation on the fault plane is 280 cm. The rupture started near the bottom of the fault plane and propagated toward the surface. Stress drop associated with faulting was Δσ = 70 bars, and the seismic moment was M0 = 16.4 × 1025 dyne cm.