An Investigation into Time-Dependent Fault Zone Properties at Seismogenic Depth on the San Andreas Fault near Parkfield

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). This project aims to improve our understanding of the nucleation process of earthquakes by contributing better seismological constraints of time-dependent fault zone properties at seismogenic depth. The availability of a large number of high-quality seismic data from a dense borehole seismograph network at Parkfield, California introduces opportunities for unraveling detailed view of subsurface fault-zone properties. We seek to develop new approaches to take advantage of numerous identified sequences of characteristic repeating earthquakes, and to determine three time-dependent properties at seismogenic depth: 1) fault-zone strength, 2) rheological behaviors, and 3) anelastic model of the inner fault zone. The project will explore temporal variations in source properties of repeating earthquake sequence as a proxy for changes in fault strength to gain a better understanding of the role of time-dependent fault strength on the mechanics of fault deformation and the earthquake nucleation process. We seek to significantly expand repeating seismicity data to allow for much improved spatiotemporal resolution of fault strength along the San Andreas Fault. The other focuses of this project will involve understanding space- and time-varying rheological properties at depth and imaging transient or systematic structural changes within the narrow fault core in the postseismic period following the 2004 M6 Parkfield earthquake. This project will investigate time-varying fault-zone strength at seismogenic depth that will effect the triggering and sequencing of earthquakes, by taking the advantage of the numerous identified repeating earthquakes accumulating from a dense borehole seismograph network at Parkfield, California. The other activities of this project will explore spatiotemporal variations in fault-zone rheological properties and will characterize temporal changes in the central core of fault zone in postseismic deformation period, in order to gain a more comprehensive picture of the role of time-varying fault zone properties on the earthquake nucleation process. The project will directly contribute improved estimates of earthquake potential on the San Andreas Fault by improved knowledge of subsurface time-dependent fault zone properties. Results from the project will be used in earthquake hazard mitigation efforts by local communities and organizations. The project will include the education and research of a graduate student.