abstract

Group velocities for Rayleigh waves extending to 140-sec-period range have been determined for 10 paths in the Indonesia-Philippine region using moving window analysis. The group velocities for five of these paths have been determined from the vertical as well as the longitudinal components and the values obtained from the two components tally with each other. It has also been possible to obtain Love-wave group velocities for three of these paths. On the basis of group-velocity values and regions covered, the observed Rayleigh-wave group-velocity data could be divided into three groups. The first group includes data for paths mostly confined to deep ocean and the observed data could be explained by standard oceanic models such as 8099. The second group includes data for paths lying partially within seismically active regions and models ARC-1 and ALRDG-9 fit with these data. The third group shows still lower group velocities for paths entirely confined to seismically active regions. The shear velocities inferred from Love-wave dispersion data are higher than those inferred from Rayleigh-wave data. In general, the group velocities varied greatly within small distances even in the longer period range, indicating strong lateral heterogeneities in the mantle.

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