SCEC Award Number 18037 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 Chunquan Yu, Postdoc
SCEC Priorities 1d, 1e, 3a SCEC Groups Seismology, CXM, CSEP
Report Due Date 03/15/2019 Date Report Submitted 03/08/2019
Project Abstract
 For a decade UCSD and Caltech have worked on improving earthquake locations and focal mechanisms, and systematically estimating stress drops from source spectra. Our results have produced a large improvement in earthquake location accuracy for small earthquakes and dramatically sharpened seismicity features in southern California, while providing insight into fault zone processes (see Figure 1). We have also produced large catalogs of focal mechanisms and Brune-type stress drop estimates, which have facilitated large-scale analyses of the stress state of the southern California crust. This work has led to a substantial body of published results, both by our group and by others who have used our data products in their own research.
During 2018, we further refined earthquake locations and focal mechanisms. We also developed a new method for seismic imaging of the Moho beneath thick sedimentary basins, which is challenging as low-velocity materials often cause strong reverberations that mask desired signals from the Moho. Instead, we take advantage of the sedimentary effect and develop a new method to image the Moho. The new method utilizes the first Pn crustal multiple from regional earthquakes, PnPn, and its differential travel time with respect to Pn to constrain the depth of the Moho. PnPn is usually weak in amplitude and thus is difficult to identify for a normal crust without sediments.
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 3