Coseismic fault slip associated with the 1992 M_w 6.1 Joshua Tree, California, earthquake: implications for the Joshua Tree-Landers earthquake sequence

Coseismic surface deformation associated with the M_w 6.1, April 23, 1992, Joshua Tree earthquake is well represented by estimates of geodetic monument displacements at 20 locations independently derived from Global Positioning system and trilateration measurements. In order to determine the long-wavelength distribution of slip over the plane of rupture, a Tikhonov regularization operator is applied to these estimates. The resulting slip distribution yields a geodetic moment estimate of 1.7 × 10¹⁸ N m with corresponding maximum slip around 0.8 m. Stress drop estimates are in the range of 2-4 MPa. Most of the aftershocks occur in areas for which the mainshock rupture produced stress increases larger than about 0.1 MPa. In contrast, predicted stress changes are near zero at the hypocenter of the M_w 7.3, June 28, 1992, Landers earthquake. Based on aftershock migrations and the predicted static stress field, it is speculated that redistribution of Joshua Tree-induced stress perturbations played a role in the spatio-temporal development of the earthquake sequence culminating in the Landers event. -from Authors