Article

An automatic, adaptive algorithm for refining phase picks in large seismic data sets

Bulletin of the Seismological Society of America (Impact Factor: 1.94). 06/2002; 92:1660-1674. DOI: 10.1785/0120010224

ABSTRACT We have developed an adaptive, automatic, correlation- and clustering-based method for greatly reducing the degree of picking inconsistency in large, digital seismic catalogs and for quantifying similarity within, and discriminating among, clusters of disparate waveform families. Innovations in the technique include (1) the use of eigenspectral methods for cross-spectral phase estimation and for providing subsample pick lag error estimates in units of time, as opposed to dimensionless relative scaling of uncertainties; (2) adaptive, cross-coherency-based filtering; and (3) a hierarchical waveform stack correlation method for adjusting mean intercluster pick times without compromising tight intracluster relative pick estimates. To solve the systems of cross-correlation lags we apply an iterative, optimized conjugate gradient technique that minimizes an L1-norm misfit. Our repicking technique not only provides robust similarity classification-event discrimination without making a priori assumptions regar

1 Bookmark
 · 
113 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: We compute high-precision earthquake locations using southern California pick and waveform data from 1981 to 2005. Our latest results are significantly improved compared to our previous catalog by the following: (1) We locate events with respect to a new crustal P and S velocity model using three-dimensional ray tracing, (2) we examine six more years of waveform data and compute cross-correlation results for many more pairs than our last analysis, and (3) we compute locations within similar event clusters using a new method that applies a robust fitting method to obtain the best locations satisfying all the differential time constraints from the waveform cross correlation. These results build on the relocated catalogs of Hauksson and Shearer (2005) and Shearer et al. (2005) and provide additional insight regarding the fine-scale fault structure in southern California and the relationship between the San Andreas Fault (SAF) and nearby seismicity. In particular, we present results for two regions in which the seismicity near the southern SAF seems to align on dipping faults.
    Journal of Geophysical Research 01/2007; 112. · 3.17 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The availability of seismic bulletin sources presents a problem when preparing data sets for studies. With so many choices, which catalog should be used? We have developed a method of merging data from all available seismic bulletins into a single database of non-redundant phases for each event. With this new database, additional ground truth (GT) events are readily identified due to the merging of all possible arrivals for each event. The compilation of over 8500 GT25 or better events in Asia allows the generation of large-scale travel time correction surfaces. We have created Pg, Pn, P, Sg/Lg, Sn, and S surfaces for the 1382 current and historic stations that detected a GT event. The availability of correction surfaces for any and all stations in a large region permit relocations that result in greater accuracy and increased event clustering for entire seismic catalogs.
    08/2007;
  • [Show abstract] [Hide abstract]
    ABSTRACT: This integrated study of deep earthquake locations and focal mechanisms investigates the relationship between the shape of subducting slabs and seismic behaviour in Wadati-Benioff zones. High quality earthquake locations are used to map the shapes of subducting slabs which have reached the upper-lower mantle boundary. The resulting slab models reveal the presence of large slab folds in the mantle transition zone. The distributions and focal mechanisms of deep earthquakes are analysed to determine whether these folds have a role in governing Wadati-Benioff zone seismicity. Bands or lineations of dense seismicity are associated with the hinge zones of identified folds. The focal mechanisms of earthquakes within these bands reveal that the mapped fold hinges are commonly perpendicular to the directions of maximum coseismic extension and compression. The hinges plunge at a variety of angles, resulting in systematic deviations from the downdip stress field expected within planar slabs. Slab synforms are typified by earthquake focal mechanisms indicating in-plane compression (e.g. Izu-Bonin, Tonga), while antiforms have earthquake focal mechanisms indicating in-plane extension (e.g. Solomons) or a mixture of in-plane compression and extension (e.g. Tonga). Slab buckling explains both the clustering of earthquakes and the observed focal mechanism orientations within fold hinges. The localization of strain within buckle zones results in several of the peaks observed in regional earthquake depth distributions. During buckling, the directions of maximum shortening and extension are expected to be perpendicular to the fold hinges, in agreement with deep earthquake moment tensors. Displacement of the minimum-strain surface away from the centre of each seismogenic zone can explain the predominance of in-plane compression within synforms and in-plane extension within antiforms. More complex local variation in focal mechanism orientations in the Tonga slab can be explained by a superposition of in-plane compression and bending strain. Buckling appears to be a common mechanism facilitating convergence between subducting slabs and the lower mantle. The consequent rotation and translation of fold limbs may explain the discrepancy between estimates of convergence based on subduction velocities and long-term coseismic strain.
    Geophysical Journal International 02/2013; 192(2):837-853. · 2.85 Impact Factor

Full-text (2 Sources)

View
47 Downloads
Available from
Jun 2, 2014