期刊
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
卷 117, 期 -, 页码 -出版社
AMER GEOPHYSICAL UNION
DOI: 10.1029/2011JB009122
关键词
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资金
- National Science Foundation grants [EAR-0838346, EAR-1045856]
- Division Of Earth Sciences
- Directorate For Geosciences [1045856] Funding Source: National Science Foundation
We revisit the rupture zone of the 1989 Mw6.9 Loma Prieta earthquake, central California, by developing high-resolution three-dimensional (3-D) V-p and V-p/V-s models. We apply the simul2000 inversion method and algorithm to a set of composite events, which have greater number of picks per event and reduced random picking errors compared with traditional master events. Our final P-wave velocity model generally agrees with previous studies, showing a high velocity body of above 6.7 km/s in the southeast rupture zone of the main shock. The 3-D V-p/V-s model, however, has different features, with low Vp/Vs in the upper crust and high V-p/V-s anomalies in deeper layers of the rupture zone. We interpret the low V-p/V-s at shallow depths to be granitic rocks, whereas at greater depths the areas of higher V-p/V-s (around 1.725-1.75) presumably are mafic rocks. The resulting 3-D velocity model was used to improve absolute locations for all local events between 1984 and 2010 in our study area. We then applied a similar event cluster analysis, waveform cross-correlation, and differential time relocation methods to improve relative event location accuracy. Over 88% of the seismicity falls into similar event clusters. A dramatic sharpening of seismicity patterns is obtained after using these methods. The medians of the relative location uncertainties calculated by using the bootstrap approach are 5 m for horizontal and 8 m for vertical. Differential times from cross-correlation are used to estimate in situ near-source V-p/V-s ratio within each event cluster. The high-resolution V-p/V-s method confirms the trend of the velocity variations from the tomographic results, although absolute values are slightly different.
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