Regional Model Calibration for Improving Seismic Location
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.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE Office of Defense Programs (DP) (US)
- DOE Contract Number:
- W-7405-Eng-48
- OSTI ID:
- 791758
- Report Number(s):
- UCRL-JC-138983; TRN: US200302%%755
- Resource Relation:
- Conference: 22nd Annual Department of Defense/Department of Energy Seismic Research Symposium, New Orleans, LA (US), 09/12/2000--09/15/2000; Other Information: PBD: 14 Jul 2000
- Country of Publication:
- United States
- Language:
- English
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