HR: 16:30h
AN: S22F-03    [PDF]
TI: Location Calibration in East Asia: Final Results of a Consortium Project, and Lessons Learned
AU: * Richards, P G
EM: richards@LDEO.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Armbruster, J
EM: armb@LDEO.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Khalturin, V I
EM: vkhaltur@LDEO.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Kim, W
EM: wykim@LDEO.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Schaff, D
EM: dschaff@LDEO.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Waldhauser, F
EM: felixw@LDEO.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Burlacu, V
EM: burlacu@pidc.org
AF: Mission Research Corporation, 8560 Cinderbed Rd Suite 700, Newington, VA 22122 United States
AU: Burlacu, V
EM: burlacu@pidc.org
AF: University of Wyoming, Earth Sciences, P.O. Box 3006, Laramie, WY 82070 United States
AU: Fisk, M D
EM: fisk@neutron.mrcwdc.com
AF: Mission Research Corporation, 8560 Cinderbed Rd Suite 700, Newington, VA 22122 United States
AU: Morozov, I
EM: morozov@uwyo.edu
AF: University of Wyoming, Earth Sciences, P.O. Box 3006, Laramie, WY 82070 United States
AU: Morozova, E
EM: lena@uwyo.edu
AF: University of Wyoming, Earth Sciences, P.O. Box 3006, Laramie, WY 82070 United States
AU: Cormier, V
EM: cormier@geol.uconn.edu
AF: University of Connecticut, Dept. of Geology and Geophysics, Storrs, CT 06269 United States
AU: Stroujkova, A
EM: stroujko@uconnvm.uconn.edu
AF: University of Connecticut, Dept. of Geology and Geophysics, Storrs, CT 06269 United States
AU: Saikia, C
EM: Chandan_Saikia@urscorp.com
AF: URS Group, Inc., 566 El Dorado Rd, Pasadena, CA 91101 United States
AB: We have developed and tested Source Specific Station Corrections (SSSCs) for Pn and Sn travel times at 30 International Monitoring System stations in East Asia, and for 127 other stations used for validation testing. We developed a 3D model of the P--wave velocity for East Asia (using 36 different 1D regions), and used 3D ray tracing in the aggregate model to compute SSSCs. These model--based SSSCs were refined empirically by kriging travel--time residuals for ground--truth (GT) events. Off--line validation tests were performed by relocating GT events, with and without using SSSCs. Nuclear explosions dominated our ground--truth datasets in this project for much of Russia and Central Asia, but it was also necessary to develop GT information on significant numbers of earthquakes, for example to calibrate stations in China. Using the double--difference method and detailed fault maps, we obtained 64 GT5 earthquakes by re-analyzing the Annual Bulletin of Chinese Earthquakes for a 15-year period (1985 to 1999). Other reference events were provided by special studies, and in some cases contributed by colleagues. Using Pn and Sn arrival times for our GT data sets, we relocated 525 events recorded by various combinations of 140 regional stations. Mislocations were reduced for 66% of the events using the model--based SSSCs, and for 85% of the events using model--based SSSCs refined by kriging. Median mislocation improved from 16.9~km to 11.4~km and 6.5~km, respectively. Median error ellipse area was reduced from 2,616~km$^{2}$ to 1,633~km$^{2}$ and 722~km$^{2}$, respectively. Error ellipse coverage (percentage of GT locations within 90% error ellipses) was 89% without using SSSCs, 91% using model--based SSSCs, and 92% using kriged SSSCs. These results were obtained for source--station paths that sample diverse geological provinces throughout much of Asia. The SSSCs are expected to perform, on average, as well as the test results using the model--based SSSCs, and substantially better for areas where GT calibration data were utilized to refine the SSSCs. Our overall method (of first obtaining model travel times and then kriging with empirical data) is well suited to calibration of any stations in East Asia that have a significant archive of reliably measured arrival times. The method potentially has global application, to greatly improve global bulletins of seismicity without having to rely wholly upon a 3D model of Earth's seismic velocity. But an international long--term effort is needed to build the necessary reference events.
DE: 6309 Decision making under uncertainty
DE: 7215 Earthquake parameters
DE: 7219 Nuclear explosion seismology
DE: 9320 Asia
SC: Seismology [S]
MN: 2003 Fall Meeting