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This paper discusses cruxes of the method for inverting the P-time residual data introduced by Aki et al. (1976a) and summarizes the results obtained by the method on 3-dimensional seismic velocity anomalies in the lithosphere under several seismic arrays around the world. The velocity anomalies at shallow depths correlate well with geologic features in young, active areas such as California, Hawaii, and Yellowstone, but the correlation is not apparent in old, stable areas such as eastern Montana and Norway. Significant small scale (20~50 km) lateral inhomogeneity is observed everywhere to the depth of 100~150 km, with the minimum estimate of root mean square fluctuation about 3%. The lithosphere-asthenosphere boundary seems to manifest itself as change in the roughness of anomaly pattern or in the trend of anomaly.
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