SCEC Award Number 17229 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Constraining the Fault Zone Architecture of the San Jacinto Fault Zone using Trapped Wave Normal Mode Oscillation, Particle Motion, and Ambient Noise Recorded on Dense Seismic Arrays
Investigator(s)
Name Organization
Amir Allam University of Utah
Other Participants Elizabeth Berg (PhD Student)
Yadong Want (PhD Student)
1-2 Undergraduate Assistants
SCEC Priorities 3e, 3a, 3c SCEC Groups Seismology, FARM, CXM
Report Due Date 06/15/2018 Date Report Submitted 05/06/2019
Project Abstract
 We investigated the distribution, asymmetry, along-fault variation, and intensity of fault damage zones and bimaterial interfaces along the San Jacinto fault zone using dense temporary seismic array deployments. We employed diverse techniques including ambient noise cross-correlation, double beamforming, teleseismic arrival time analysis, wave equation dispersion inversion, and trapped wave resonance. These techniques were applied to three across-fault arrays of >100 temporary three-component seismometers, one of which was funded by the proposal. The arrays were placed along three mechanically distinct segments of the fault zone: the extensional Hemet Stepover, the simple linear Anza segment, and the complexly deformed Trifurcation area. The results include the first ever observation of the full spatial eigenfunction of trapped wave normal modes (in prep), the first ever damage zone images produced by double beamforming of ambient noise cross-correlations (in prep), the first damage zone imaging from a new wave equation dispersion method (Li et al., 2019), and the highest resolution images of the damage zone in the Hemet stepover (Share et al., 2019). The three along-fault arrays are groundbreaking first-of-their kind deployments which will provide important data for years to come. In this technical report, I will describe the proposed work, demonstrate how the objectives were met or modified, and summarize the results to date.
Intellectual Merit he results include the first ever observation of the full spatial eigenfunction of trapped wave normal modes (in prep), the first ever damage zone images produced by double beamforming of ambient noise cross-correlations (in prep), the first damage zone imaging from a new wave equation dispersion method (Li et al., 2019), and the highest resolution images of the damage zone in the Hemet stepover (Share et al., 2019). The three along-fault arrays are groundbreaking first-of-their kind deployments which will provide important data for years to come.
Broader Impacts The SJFZ is one of the most hazardous faults in California; efforts to improve the understanding of seismic hazard benefit the residents of Southern California. The array deployments employed 11 undergraduate assistants and 9 graduate researchers, providing valuable experience in geophysical field methods. The published work produced by this funded proposal consists entirely of peer-reviewed articles with student primary authors. This work has provided significant motivation to greatly expand the pool of Nodal seismometers available at the University of Utah (expanded from ~100 to 210 seismometers since this proposal was funded) and at the PASSCAL instrument center. This work is the first to use fault zone array deployments of these inexpensive three-component instruments, and represents the state-of-the-art in use of this technology and analysis of the resulting data.
Exemplary Figure Figure 3: (a) Vertical-vertical cross-correlations for the BS array showing clear Rayleigh waves in three different period bands. (b) Example trapped waves recorded at the BS array from a M2.5 event at 56km distance from the array. Seismograms are 3Hz low-passed vertical components. (c) The energy from 83 events recorded on the array. More detail provided in the text. (d) The final inverted shear-wave velocity for the RR array, showing several low velocity zones which narrow with depth that correlate with the earthquake trapped wave distribution. (Figure by Yadong Wang)