Constraining Non-Linear Lithospheric Viscous Flow Laws From Postseismic Surface Deformation Measurements

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

EAR-0207617 Roland Burgmann This project relies on observations of postseismic surface deformation following the 1992 Landers and 1999 Hector Mine earthquakes to infer the flow laws that characterize the apparent non-linear viscous rheology of the lithosphere beneath the Mojave Desert. Non-linear or power law behavior, in which strain rate is proportional to stress raised to a power and exponentially dependent on temperature, has been demonstrated in laboratory experiments and surmised from an inferred change in effective linear viscosity following the Mojave quakes. However, the specific non-linear flow laws that characterize the rheology of the Mojave lithosphere have not been determined. Non-linear rheology has been difficult to infer in the past due to a lack of sufficiently resolved observational constraints. The unprecedented GPS and InSAR coverage of postseismic deformation following the Mojave quakes, combined with the ability to numerically model complex slip distributions and non-linear rheology, allow for the determination of the appropriate flow law parameters governing continental lithospheric behavior in this region. The work consists of compiling the geodetic data sets in a form useful for constraining a numerical model and development of a 3-D viscoelastic finite element model of the Landers and Hector Mine ruptures. This constrained model is used to (1) partition postseismic deformation between viscous processes and other mechanisms such as afterslip, (2) determine the depth distribution of viscous flow, and (3) infer applicable non-linear flow laws. The results provide insight into how forces generated within the Earth's interior manifest themselves at the surface and how stresses induced by earthquakes are redistributed during interseismic periods. The latter of which is important to understanding seismic hazards. An additional byproduct of this research consists of guidelines for conducting future geodetic investigations of non-linear lithospheric rheology by noting the most useful locations for instrumentation relative to strike-slip earthquakes.