Global Rayleigh wave phase-velocity maps from finite-frequency tomography

We report global phase-velocity maps of fundamental-mode Rayleigh waves at periods between 25 and 100 s based on finite-frequency tomography. Rayleigh wave dispersion measurements are made using a multitaper technique for both minor-arc and major-arc wave trains. The global phase-velocity maps confirm many features associated with surface tectonics including the ocean-continent dichotomy and the signature of lithospheric cooling in oceanic plates. In addition, the high-resolution phase-velocity maps reveal a major change in the distribution of small-scale anomalies in the Pacific at different wave periods. We calculate the global average of Rayleigh wave phase velocity in major tectonic regions and show that large discrepancies exist between our model and global crustal and mantle models: (1) In oceanic regions, short-period (<similar to 40 s) Rayleigh waves are faster than calculations based on models CRUST2.0 and S40RTS. The discrepancies could be explained by a thinner crust or faster wave speeds in the crust or upper mantle. The implementation of model CRUST1.0 significantly improves the agreement, with phase-velocity discrepancies less than 0.5 per cent on average. (2) In Archean cratons, Rayleigh wave phase velocities in our model are faster than calculations based on model S40RTS at periods longer than similar to 40 s; and the global average in orogenic belts is similar to 1-2 per cent slower than CRUST1.0 at periods shorter than similar to 50 s.US National Science Foundation [EAR-1013617, EAR-1348131]; National Natural Science Foundation of China [41374047]; College Foundation of Yunnan University [2015CG002]SCI(E)EIARTICLElkui@vt.edu151-6620