HR: 0800h
AN: S51B-0158    [Abstracts]
TI: Waveform Cross-Correlation Analysis of Seismic Data From the Costa Rica Seismogenic Zone
AU: * Hansen, S E
EM: shansen@es.ucsc.edu
AF: University of California, Santa Cruz, Earth Science Department 1156 High St., Santa Cruz, CA 95064 United States
AU: Schwartz, S Y
EM: susan@es.ucsc.edu
AF: University of California, Santa Cruz, Earth Science Department 1156 High St., Santa Cruz, CA 95064 United States
AU: DeShon, H R
EM: hdeshon@es.ucsc.edu
AF: University of California, Santa Cruz, Earth Science Department 1156 High St., Santa Cruz, CA 95064 United States
AB: Earthquakes nucleating within the seismogenic zone at convergent margins generate more than 80% of the total world-wide seismic moment release and can pose significant seismic hazard to coastal areas. The mechanical behavior along the seismogenic zone is not well understood due to the limited constraint on the precise geometry (thickness of the planar interface as well as the up- and down-dip limits) and the degree of plate coupling in these regions. The 1999-2001 collaborative Costa Rica Seismogenic Zone Experiment (CRSEIZE) consisted of a joint seismic and geodetic investigation of the Costa Rica plate interface to learn about the processes occurring at subduction margins. As part of this study, two seismic transects were established across the Middle America Trench at the Nicoya and Osa Peninsulas in Costa Rica and velocities at 46 GPS sites throughout the country were determined. The seismic arrays consisted of both land and ocean bottom broadband and short-period stations situated directly above the seismogenic zone, allowing for direct recording of local seismicity. Ongoing work includes determination of earthquake locations and the three-dimensional P- and S-wave velocity structure in northern Costa Rica using local seismic tomography. Currently, waveform cross-correlation techniques to improve P- and S-wave arrival times are being incorporated. The automated correlation and clustering method employed greatly reduces the picking inconsistencies compared to human analysis alone and has improved relative relocations allowing previous determinations of the up- and down-dip limits of the seismogenic zone to be refined. More importantly, waveform cross-correlation has improved P-wave first-motion determinations for many events, resulting in more abundant and reliable focal mechanisms. This improves our ability to differentiate between underthrusting interplate events and intraplate seismicity. In addition, the degree of waveform similarity has been assessed to identify repeating earthquakes. In northeastern Japan, waveform similarity studies have revealed that numerous earthquakes generated by repeated slip at small asperities, with recurrence intervals on the order of months, occur only on the plate boundary (Igarashi et al., 2003). Our analysis in northern Costa Rica has identified many clusters of similar events, both above and below the plate interface; however, unlike NE Japan, we find no evidence for repeating events that generate identical waveforms at the same stations. These combined results allow for improved characterization of seismogenic zone processes.
DE: 7230 Seismicity and seismotectonics
DE: 7200 SEISMOLOGY
SC: Seismology [S]
MN: 2004 AGU Fall Meeting