SCEC Award Number 25108 View PDF
Proposal Category Individual Research Project (Single Investigator / Institution)
Proposal Title High Resolution Catalogs of Template Earthquakes and Focal Mechanisms for Resolving Fine-Scale Fault Structures and Crustal Rheology
Investigator(s)
Name Organization
Egill Hauksson California Institute of Technology
SCEC Milestones A2-3, B2-1, D2-2 SCEC Groups Seismology, CEM, EFP
Report Due Date 03/15/2026 Date Report Submitted 03/06/2026
Project Abstract
 We propose to refine and update earthquake hypocenters (Hauksson et al., 2012) and focal mechanisms (Yang et al., 2012) for southern California. The SCEC community will use the updated catalogs to address research problems, such as refine community models, fine-scale fault structures, source studies, and rheological properties, as well as applying template matching to generate high resolution catalogs.

In particular, we propose to:
1) Extend the southern California refined (1981-2024) catalogs of relocated hypocenters (templates) and focal mechanisms by adding one more year (2025) of data.
2) Improving the methodology with new algorithms (NonLinLog and GrowClsut3D.jl) and 3D velocity models.
3) In case of significant new seismic activity, we will update the catalogs and use the refined relocated hypocenters and focal mechanisms to improve our understanding of such activity, including the seismotectonics, earthquake forecasting, and seismic hazards.
4) Participate in relevant SCEC working groups to facilitate application of the catalogs.

This research will provide detailed understanding of earthquake source properties and their temporal variations, which will contribute to the community fault model, 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. In addition, events in this catalog will be used as templates in machine learning algorithms to search for previously undetected smaller events, which could on average add up to a factor of 10 more events to the catalog (Ross et al., 2019).
SCEC Community Models Used Community Fault Model (CFM), Community Velocity Model (CVM), Community Stress Model (CSM), Community Thermal Model (CTM)
Usage Description The data refined in our study, has contributed to the development of CFM, CSM, CVM, and other SCEC community models.
Intellectual Merit This research is foundational to detailed understanding of earthquake source properties and their temporal and spatial variations. In addition, it contributes to the Community Fault Model (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 have provided rapid identification of the rupture planes. In addition, events in this catalog will be used as templates in machine learning algorithms to search for previously undetected smaller events, which could on average add up to a factor of 10 more events to the catalog.
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, b) mapping of the geophysical properties of fault zones, c) 3D velocity model inversions, d) stress drop determinations, e) rheological properties of the crust, f) earthquake statistics, g) identification and monitoring of anthropogenic seismicity, h) aftershock studies, and i) stress field determination. In addition, various public presentations or hazards reports done by earth scientists may include seismicity maps to explain local earthquake activity.
Project Participants The PI did all the research, including data processing, software maintenance, and interpretation of the results. P. Shearer of UCSD has been involved as a partner to develop the methodology and software.
Exemplary Figure Figure 1. The HS catalog (1981 – 2025). 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. LA: City of Los Angeles.
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