| We present a high-resolution, three-dimensional S-velocity model of the upper mantle beneath the Western Pacific and Southeast Asia. We develop a novel Automated Multimode Inversion (AMI) technique that allows us to process a very large waveform data set with high accuracy. Information on upper mantle structure is obtained from vertical-component broadband seismograms, using the time and frequency windows that do not contain significant amounts of scattered energy. The time windows include both the fundamental Rayleigh mode and the S and multiple S waves, the body waves often triplicated. 4038 seismograms constrain the resulting tomographic model down to the 660-km discontinuity. The lateral resolution is about 400 km; velocity contrasts are located with a 100–400 km precision. Automated Multimode Inversion of surface waves proves an efficient technique for high-resolution upper-mantle imaging and presents opportunities for future developments that should further enhance tomographic resolution.; The tomographic model offers new insights into the structure and dynamics of the SE Asia upper mantle. The western Yangtze Craton displays a signature of pronounced continental tectosphere; a strong high-velocity anomaly extends down to 300–350 km and continues about 500 km northwest outside of the cratonic boundaries; it is particularly fast beneath the Sichuan Basin. In the Sino-Korean Craton, the Archean Ordos Basin is fast down to 200–250 km depth; the eastern part of the craton is slow in the upper 250 km of the mantle. The Songliao Basin to the north of the craton is fast, at least down to 300 km; in agreement with geologic data, the fast ancient lithosphere of the Songliao Block extends west of the present boundaries of the basin. A pattern of deep high-velocity anomalies dominates the transition zone. The fastest anomaly, estimated to be up to 4–5%, is beneath the Bohai Gulf. The top of the fast anomaly is at a 250–300 km depth. The anomaly continues to the north under the Songliao Basin and to the southwest under the Sichuan Basin. Near Hainan, a continuous low-velocity anomaly reaches the lower transition zone, providing evidence for deep-mantle origin of the OIB-type basalts in the circum South China Sea region. |
