An elastic rebound model for normal fault earthquakes

Abstract

A viscoelastic finite element method is used to formulate an elastic rebound model for normal fault earthquake cycles. Model generated displacements correlate well with geodetic survey data collected before and after the 1954 (M = 7.1) Fairview Peak, Nevada, and the 1959 (M = 7.1) Hebgen Lake, Montana, earthquakes. Model coseismic deformation results in an uplift of the footwall block and a depression of the hanging wall block as has been reported by Savage and Hastie (1966). The interseismic phase of the deformation is characterized by a regional doming of the crust in the vicinity of the modeled normal faults. Doming observed before and after and adjacent to the faults which ruptured during the Hebgen Lake earthquake, indicate that areas which are experiencing doming may be the future sites of normal fault earthquakes. Two areas which are presently experiencing crustal doming and are in the vicinity of a normal fault are the Socorro, New Mexico, and Diablo plateau, Texas (Brown et al., 1978), regions. The interseismic doming will not occur if the modeled fault ruptures through the entire lithosphere. If a single normal fault is active, then model generated coseismic and interseismic deformations result in (sum to) a tilt block topography. If two normal faults are active, one master fault and a minor fault which dips toward the master fault, then the resultant deformation is a horst and graben type of topography. The rate at which the doming proceeds is primarily a function of the seismic stress drop and the effective viscosity of the asthenosphere. Doming rates following the Hebgen Lake earthquake indicate an asthenospheric viscosity of about 2 × 1021 P. Model recurrence intervals for the Fairview Peak and Hebgen Lake earthquakes are on the order of 103 yr.