Robust inversion of IASP91 travel time residuals for mantle P and S velocity structure, earthquake mislocations, and station corrections
- Lawrence Berkeley Lab., CA (United States)
- Univ. of California, Berkeley, CA (United States)
- Univ. of California, San Diego, CA (United States)
Using both P and S arrival time information, 41,108 events in the International Seismological Centre (ISC) catalog for the years 1964 to 1987 are relocated relative to the IASP91 velocity model. The mean absolute horizontal relocation is 7.7 km and the mean absolute depth relocation is 9.1 km. The mean absolute origin time shift is 1.2 s. The relocation procedure increased the P residual standard deviation slightly from 2.3 s to 2.5 s while decreasing the S residual standard deviation from 6.8 s to 6.1 s. When plotted as bottoming point averages, the resulting IASP91 P and S arrival time residuals show coherent patterns as a function of geographic location. An iterative l{sup p} residual norm minimization algorithm is used to estimate the set of P and S velocity variations as well as the earthquake relocation and seismographic station parameters which best explain the travel time residuals. The procedure is robust in that extremely large travel time residuals, which are common in the ISC data, do not unduly influence the velocity estimates. It is only in the lowermost mantle, 2670 km to the core-mantle boundary, that the level of P heterogeneity rises significantly above the estimated noise level. In this depth range a partial ring around the Pacific basin is observed, although this pattern is somewhat obscured by poor resolution in the southern hemisphere. The hypocentral relocation parameters are sizable; they have a mean absolute horizontal relocation of 3.9 km and a mean absolute vertical relocation of 10.3 km. However, the event relocations do not alter the patterns of P and S velocity significantly. Deviations in P to S velocity ratios for the upper mantle are greatest (-3%) in the depth range 35-200 km beneath the oceanic trenches. Additional large variations of 2% are found below the continental cratons, particularly between the depths 200 and 400 km. 53 refs., 19 figs., 1 tab.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 41679
- Journal Information:
- Journal of Geophysical Research, Vol. 99, Issue B7; Other Information: PBD: 10 Jul 1994
- Country of Publication:
- United States
- Language:
- English
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