Collaborative Research: Understanding Fault Zone Compliance by Seismic Probing of InSAR Anomalies

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This project aims to measure how much weaker are the rocks in fault zones than the surrounding, unbroken rocks. The consortium of institutions will deploy seismometers to record explosions and earthquakes. The experiment will first decipher the structure of the crust in terms of P, S, and surface wave speeds, then interpret the wavespeed maps in terms of rock strength and crack density. The group will also measure the ground deformation over several years with GPS. These structures will be compared with the features noted with satellite deformation monitoring. The insights gatheredwill help understand why fault systems form as they do. More specifically, the spacing of faults and the frequency of earthquakes across the fault system in California is ripe for a deeper understanding, and this project will strive for progress in this direction.The investigators propose to integrate the expertise at UCLA, UCSD, and USC to systematically map the structural cross-section of the Calico and Pinto Mountain fault zones across profiles that exhibited anomalous strain in response to the Landers and Hector Mine earthquakes. They will deploy portable seismographs in both an active-source experiment to map the shallow fault structure and a passive-source experiment to image deeper structure. Their observations will test and extend previous InSAR modeling to better resolve the amplitude, width and depth of fault zone anomalies. This project will explore the structure and evolution of seismogenic faults in the Mojave using a variety of methods. The results will constrain the size of fault zone weakness and variations in strength across the earthquake cycle and lead to improved understanding of fault mechanics.This project supports educational programs at three universities, including graduate student research and field programs for undergraduates. Collaboration between institutions will be promoted by regular meetings of the PIs, students and postdocs to discuss relevant science and the state of the project. Results of this research will be widely disseminated through publications, conference presentations and media contacts, including a project website. This research will provide a better understanding of fault behavior, leading eventually to improved earthquake forecasting and reduced casualties and damage.