Project Leader:
Dr. Felix Waldhauser
Earth Institute Contact: Dr. Felix Waldhauser
Locations: United States of America
Special Locations:
Northern California, San Francisco Bay Area
Description:
We propose to use a recently completed database of cross correlation based differential time measurements to relocate all earthquakes between 1984-2001 in the catalog of the Northern California Earthquake Data Center. The database includes almost 3 billion highly accurate differential times for P- and S- waves. The P-wave differential times are typically on the order of a factor of ten to a hundred times more accurate than those obtained from routinely picked phase onsets. S-waves are not routinely picked at the Northern California Seismic Network because of their generally weak onset. Approximately 90% of the seismicity includes events that have cross-correlation coefficients of CC>0.7, with at least one other event recorded at four or more stations. We therefore expect substantial improvement in hypocenter locations across northern California using these new data. We will parallelize the double-difference algorithm hypoDD to relocate the events on a massive scale on a 64 processor Linux cluster. Being able to relocate earthquakes on a massive scale it is often possible to reveal new features in the data, or to perform more comprehensive analyses of problems that were previously addressed on smaller scales. We will initially focus on using the new high-resolution catalog to investigate the presence or absence of characteristic seismicity patterns such as streaks and repeating events indifferent tectonic regions across northern California in order to understand their origin, their implication on the process of faulting, and their relevance in estimating hazard.
The proposed work and subsequent analysis contributes to Regional Area 2 (Northern California), including the highly urbanized, greater San Francisco Bay region and to EHP Element III (Earthquake physics). It addresses the NC research priorities by enhancing the capabilities of seismic monitoring and by contributing to our understanding of fault mechanics, the estimation of fault slip rates, and the role of fault creep. We will release the high-resolution catalog upon completion of the project, providing the scientific community with new data to address many key scientific issues important to the NEHRP program. We regard this project as the second stop in a three step approach to improve earthquake locations in Northern California; Step 1 (completed): Improvement of seismic arrival time data; Step 2 (this proposal): Relocation of the historic catalog; Step 3: Incorporation of the new procedures into routine catalog production. Funding to carry out step 3, in collaboration with the NCSN/CISN, will be requested at a later stage.
EI Unit:
Lamont-Doherty Earth Observatory (LDEO)
Cross Cutting Themes:
Hazards and Risk
Core Disciplines:
Earth Sciences
Funding Agency:
US Geological Survey (USGS)
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