SCEC Award Number 16104 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Detailed analysis of earthquake directivity in the San Jacinto Fault zone
Name Organization
Jeff McGuire Woods Hole Oceanographic Institution Yehuda Ben-Zion University of Southern California
Other Participants Haoran Meng, USC graduate student
SCEC Priorities 2a, 3c, 3f SCEC Groups GMP, FARM, Seismology
Report Due Date 03/15/2017 Date Report Submitted 04/11/2017
Project Abstract
Several studies of the San Jacinto Fault Zone (SJFZ) over the last few years have found
evidence for contrasts of seismic velocities along with asymmetric fault-zone damage
patterns and additional observables that may result from a preferred rupture propagation
direction (time domain signatures of directivity, along-strike asymmetry of aftershocks,
reversed polarity secondary deformation structures near step overs). We proposed to
perform a systematic seismological analysis of rupture velocity and directivity for M > 3
SJFZ earthquakes that can be compared to and augment the existing results. In 2016 we
had two primary accomplishments. First, the fundamental EGF technique and MATLAB
inversion toolbox were published in the SRL Electronic Seismologist section making
them available to anyone who wants to use them. Second, we have made considerable
progress in automating the EGF deconvolution based measurements of directivity effects
for earthquakes in Southern California. We developed both an multi-EGF stacking
method and routines for automatically choosing the duration of the source time function
at each station. These improvements have resulted in roughly a factor of two increase in
the number of available measurements for a given earthquake and the possibility of
automating the technique for large datasets.
Intellectual Merit Moderate earthquakes are not well suited for finite fault inversions
because of a lack of geodetic data to help improve the uniqueness of the solution.
However, their finite source properties are still well resolved from seismic data in a gross
sense. The second moments inversion procedure is a relatively novel approach that
quantifies the length, width, duration, and propagation velocity of a rupture in a well
constrained (6 parameter) inverse problem. Our formulation is general, e.g. applicable to
any earthquake without bias. The SJFZ dataset is unique in Southern California in terms
of the density of on-scale recordings of magnitude 4-5 earthquakes. We are developing
the first real catalog of rupture velocity estimates for earthquakes in this magnitude range.
Broader Impacts A USC graduate student is being trained in the second moment
inversion approach to carry this work forward. The MATLAB toolbox and inversion
scheme have been made publicly available via SRL for any interested users.
Exemplary Figure Figure 3, Haoran Meng