SCEC Award Number 16050 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title SCEC Community Data Products of Relocated Seismicity and Improved Focal Mechanisms, for Resolving Fine-Scale Fault Structures and State of Stress in Southern California
Name Organization
Egill Hauksson California Institute of Technology
Other Participants Dr. Qiong Zhang, Postdoc
SCEC Priorities 2a, 2d, 2f SCEC Groups USR, EFP, Seismology
Report Due Date 03/15/2017 Date Report Submitted 03/14/2017
Project Abstract
The latest version of our waveform-relocated catalog (the HYS catalog) contains high-precision locations of over 597,000 earthquakes from 1981 through 2016.
In 2016 we focused on analyzing how the earthquakes focal depths depend on the velocity model used. Earthquake focal depths are difficult to determine because they are strongly dependent on the availability of P and S travel time data and the velocity model. We investigate how refined velocity models could possibly improve depth determination for the refined SCN catalog. Using a velocity model obtained from the waveform tomography as starting model (Lee et al., 2014), we invert for a new model that fits the P and S travel times best. We find out that focal depths relocated with the new model or with the waveform tomography model are shallower than those relocated with a previous travel time tomography model. In addition, the relative locations cluster differently, forming fewer but larger clusters.
Intellectual Merit This project relates to many key SCEC objectives and will improve our understanding of earthquake activity across southern California. In particular, our high-resolution earthquake locations provide better delineation of fault structures and make possible more advanced seismicity studies by us and other SCEC researchers. Our focal mechanism catalogs and stress drop analyses provide fundamental insights into the earthquake rupture process and the relationships between micro-earthquake activity, the crustal strain field, and major faults.
Broader Impacts Outreach activities consist of providing the relocated catalog to SCEC scientists and others doing research on seismicity in southern California. The relocated catalog is available at the Southern California Earthquake Data Center (SCEDC). We have also presented results at SCEC workshops.
Exemplary Figure Figure 1. (Exemplary Figure) Event locations from the HYS catalog (1981 – 2016). Similar-event clusters that have been relocated by using waveform cross-correlation are shown in black. Events in the SCSN catalog (and uncorrelated events in the other catalogs) are shown in brown. Events with M ≥ 5.5 are shown as stars. Faults are from Jennings (2010) with late Quaternary faults in shades of red (Hauksson et al. 2012).

Hauksson, E. and W. Yang, and P. M. Shearer (2012), Waveform Relocated Earthquake Catalog for Southern California (1981 to June 2011); Bull. Seismol. Soc. Am., 102, no. 5, 2239–2244, doi: 10.1785/0120120010.