Tomographic study of mantle structure beneath eastern Asia
Master of Science
A high-resolution 3D P-wave velocity model of the mantle beneath eastern Asia was obtained through performing seismic travel-time tomography by using recently emerging new datasets. An improved relocation method that accounts for correlated travel-time errors among similar ray paths was applied to reduce location bias caused by unmodeled heterogeneities. The model demonstrates more distinct structures beneath eastern Asia in comparison with the one obtained by applying the standard linear relocation method. This model GAP_C1 clearly shows that vast areas of low-velocity structures dominate the upper mantle above the transition zone. The late Cenozoic volcanisms are mostly distributed above these slow anomalies, implying their deep mantle origin. In the mantle transition zone, high-velocity structures with complex configurations become more prominent. These fast anomalies are most likely subducted oceanic lithospheres stagnant in the transition zone. Furthermore, their extent could be attributed to the coexistence of slabs being subducted at different stages. However, comparing the transition zone structures in model GAP_C1 to the plate reconstructions, slabs subducted at the same stage are separated beneath the Changbai volcano and the South China Fold Belt, creating slab gaps. A model was proposed to explain this phenomenon. The slab gaps are related with the slab fragmentation that happens at the slab-slab junction when the slab with different dipping directions flattens against the top of the lower mantle.