Imaging and monitoring large crustal fault zones
Seminar by Yehuda Ben-Zion
Department of Earth Sciences
University of Southern California, Los Angeles, CA, 90089-0740, USA
The core structure of large faults typically includes bimaterial interfaces that separate rock units with different elastic properties and form the principal slip surface. Earthquake ruptures produce rock damage associated with reduction of seismic velocities and related changes to other properties such as anisotropy and attenuation. Multi-scale multi-signal imaging of crustal faults reveal hierarchical damage structures with intense core damage zones and bimaterial interfaces. Analyses of earthquake waveforms right after large earthquakes indicate significant co-seismic reduction of seismic properties that can be 30% or more in the top 500 m of the crust, followed by log(t) healing. Analyses of the ambient noise with larger time steps and lower frequencies compared to the earthquake studies detect small changes of properties. Interpreting the amplitudes of co-seismic temporal changes and depth sections sustaining the changes requires using wide range of frequencies and multiple analysis time steps.