SCEC Award Number 22044 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title SCEC Community Data Products of Earthquake Catalogs with improved Focal Depth Estimation, for Resolving Fine-Scale Fault Structures and Crustal Rheology in Southern California
Investigator(s)
Name Organization
Egill Hauksson California Institute of Technology
Other Participants
SCEC Priorities 1d, 1e, 3a SCEC Groups Seismology, SDOT, EFP
Report Due Date 03/15/2023 Date Report Submitted 02/21/2023
Project Abstract
 We have refined and updated the catalogs of earthquake hypocenters (Hauksson et al., 2012) and focal mechanisms (Yang et al., 2012) for southern California. The SCSN waveform relocated catalog that consists of 41 years of ~762,000 relocated earthquakes, includes aftershock sequences from four (M>7) mainshocks, 1992 Landers, 1999 Hector Mine, 2010 El Mayor-Cucapah, and 2019 Ridgecrest. This seismicity forms complex spatial and temporal patterns related to Pacific North America plate boundary tectonics processes. All of the M>7 mainshocks and regional seismicity that occurred outside the San Andreas Fault zone proper, image the width of the plate boundary crustal deformation zone. In general, the smaller magnitude background seismicity occurs across southern California region of low stress, elevated strain rate and heat flow. The 41 year catalog of first motions and S/P-ratio amplitudes focal mechanisms contains more than ~181,700 events. The focal mechanisms map regions of predominantly strike-slip faulting along the San Andreas Fault system. Limited regions of dip-slip or normal and reverse faulting are also identified, which are mostly related to geometrical complexities of the plate boundary.
Intellectual Merit This research continues to provide a more detailed understanding of earthquake source properties and their temporal variations. In addition it continues to contribute to the CFM, SCEC 3D velocity model, stress model, rheology model, and understanding of fault zone processes. In the case of a major earthquake, improved absolute and relative locations will provide rapid identification of the rupture planes. We also report preliminary research on repeater earthquake sequences using the waveform relocated catalog. Repeating earthquake sequences, or repeaters, are assumed to rupture at different times the same area of a fault and thus may represent the repeated rupture of an asperity.
Broader Impacts These catalogs have been and continue to be used for numerous SCEC studies such as: a) monitoring of temporal and spatial evolution of seismicity (Hauksson et al., 2022), b) mapping of the geophysical properties of fault zones (Plesch et al., 2020), c) 3D velocity model inversions (Tape et al., 2009), d) stress drop determinations, (Shearer et al, 2022), e) rheological properties of the crust, (Hauksson and Meier, 2018), f) earthquake statistics, Zaliapin and Ben-Zion (2021), g) identification and monitoring of anthropogenic seismicity.( Chen et al, 2011), h) aftershock studies (van der Elst and Shaw, 2015), and i) stress field determination (Yang and Hauksson, 2013).
Exemplary Figure Figure 1. The HS catalog (1981 – 2022). Similar-event clusters that have been relocated by using waveform cross-correlation and GrowClust are shown in black. Uncorrelated events are not plotted. Events with M ≥ 5.5 are shown as red stars. Faults are from Jennings and Bryant (2010) with late Quaternary faults shown in magenta color. The blue dashed polygon delineates the SCSN reporting area.

Credit:
Hauksson, E., & Shearer, P. M. (2022). The 1981 – 2022 Southern California Seismic Network Waveform Relocated and Focal Mechanisms Catalogs: New Seismological and Tectonic Insights. Poster Presentation at 2022 SCEC Annual Meeting. SCEC Contribution 12480