POSTSEISMIC REBOUND IN FAULT STEP-OVERS CAUSED BY PORE FLUID-FLOW

Near-field strain induced by large crustal earthquakes results in chan ges in pore fluid pressure that dissipate with time and produce surfac e deformation, Synthetic aperture radar(SAR) interferometry revealed s everal centimeters of postseismic uplift in pull-apart structures and subsidence in a compressive jog along the Landers, California, 1992 ea rthquake surface rupture, with a relaxation time of 270 +/- 45 days. S uch a postseismic rebound may be explained by the transition of the Po isson's ratio of the deformed volumes of rock fl-om undrained to drain ed conditions as pore fluid flow allows pore pressure to return to hyd rostatic equilibrium.