Application of Evolutionary Programming to Earthquake Hypocenter Determination

Abstract. We relocate 297,400 events recorded by the Southern California Seismic Network (SCSN) between 1975 and 1998 using spatially varying station terms to improve relative location accuracy. Our method uses existing SCSN P and $ picks, a smooth one-dimensional velocity model, and an iterative grid search approach based on the L1 norm. We apply empirical corrections for three-dimensional structure by computing station timing corrections that continuously vary as a function of source position. Station terms for each event are obtained by smoothing the residuals from nearby events using a natural neighbor (Delaunay) tessellation of the seismicity and then iterating until a stable set of locations and station terms is achieved. Our approach achieves relative location accuracy comparable locally to master event methods but can be applied uniformly over large regions. Median estimated standard errors for our final locations are 328 m in horizontal position and 741 m in depth. Our locations exhibit much less scatter, particularly in depth, than those of the SCSN catalog and a greater tendency to align into linear and planar features suggestive of fault structures. Our results appear comparable to, and in some cases better than, previous SCSN relocation studies using joint-hypocentervelocity inversion techniques. Plots of daytime versus nighttime events permit discrimination between clusters of natural and artificial seismicity. We observe no simple relationship between the maximum depth of seismicity and surface geology.

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Improving local earthquake locations using the L1 norm and waveform cross correlation: Application to the Whittier Narrows, California, aftershock sequence

Shearer¹

1997

J. Geophys. Res.

318

229

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Abstract. Experiments with different earthquake location methods applied to aftershocks of the October 1, 1987, Whittier Narrows earthquake in California (Moe=5.9) suggest that local event locations can be greatly improved through the use of the L1 norm, station corrections and waveform cross correlation. The Whittier Narrows sequence is a compact cluster of over 500 events at 12 to 18 km depth located within the dense station coverage of the Southern California Seismic Network (SCSN), a telemetered network of several hundred short-period seismographs.

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Application of Evolutionary Programming to Earthquake Hypocenter Determination

Cited by 8 publications

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Environmental Optimization: Applications of Genetic Algorithms

Environmental Optimization: Applications of Genetic Algorithms

Earthquake locations in southern California obtained using source‐specific station terms

Improving local earthquake locations using the L1 norm and waveform cross correlation: Application to the Whittier Narrows, California, aftershock sequence

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