Regional Model Calibration for Improving Seismic Location

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Accurate seismic event location is integral to the effective monitoring of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), as well as being a fundamental component of earthquake source characterization. To account for the effects of crustal and mantle structure on seismic travel times, and to improve seismic event location in the Middle East and North Africa (MENA), we are developing a set of radially heterogeneous and azimuthally invariant travel-time models of the crust and upper mantle for each MENA seismic station. We begin by developing an average one-dimensional velocity model that minimizes the P-phase travel-time residuals from regional through teleseismic distance at ... continued below

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3,800 Kilobytes pages

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Swenson, J.L.; Schultz, C.A. & Myers, S.C. July 14, 2000.

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Accurate seismic event location is integral to the effective monitoring of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), as well as being a fundamental component of earthquake source characterization. To account for the effects of crustal and mantle structure on seismic travel times, and to improve seismic event location in the Middle East and North Africa (MENA), we are developing a set of radially heterogeneous and azimuthally invariant travel-time models of the crust and upper mantle for each MENA seismic station. We begin by developing an average one-dimensional velocity model that minimizes the P-phase travel-time residuals from regional through teleseismic distance at each station. To do this we (1) generate a suite of 1-D velocity models of the earth, (2) compute travel times through the 1-D models using a tau-p formulation to produce standard travel-time tables, and (3) minimize the root-mean-square (rms) residuals between the P-phase arrivals predicted by each model and a groomed set of ISC P-phase arrival times (Engdahl et al., 1991). Once we have an average one-dimensional velocity model that minimizes the P-phase travel-time residuals for all distances, we repeat steps 1 through 3, systematically perturbing the travel-time model and using a grid search procedure to optimize models within regional, upper mantle, and teleseismic distance ranges. Regionalized models are combined into one two-dimensional model, using indicator functions and smoother methodologies to reduce distance and depth discontinuity artifacts between the individual models. Preliminary results of this study at a subset of MENA stations show that we are improving predictability with these models. Cross-validating the travel-time predictions with an independent data set demonstrates a marked reduction in the variance of the travel-time model error distributions. We demonstrate the improvement provided by these 2-D models by relocating the 1991 Racha aftershock sequence. We will extend our investigation to additional MENA stations, and will use our model in tandem with nonstationary empirical corrections (nonstationary Bayesian kriging) to further improve our ability to accurately predict travel times and locate seismic events in this region.

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3,800 Kilobytes pages

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  • 22nd Annual Department of Defense/Department of Energy Seismic Research Symposium, New Orleans, LA (US), 09/12/2000--09/15/2000

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  • Report No.: UCRL-JC-138983
  • Grant Number: W-7405-Eng-48
  • Office of Scientific & Technical Information Report Number: 791758
  • Archival Resource Key: ark:/67531/metadc738264

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  • July 14, 2000

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  • Oct. 19, 2015, 7:39 p.m.

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  • May 6, 2016, 4:06 p.m.

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Swenson, J.L.; Schultz, C.A. & Myers, S.C. Regional Model Calibration for Improving Seismic Location, article, July 14, 2000; California. (digital.library.unt.edu/ark:/67531/metadc738264/: accessed September 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.