摘要
We used 71670 P-wave arrival times from 3594 earthquakes recorded by the Sichuan and Yunnan seismic networks to determine the three-dimensional P-wave velocity structure in the crust and uppermost mantle beneath the southeastern Tibetan Plateau. Our results show that prominent low P-wave velocity (low-Vp) anomalies exist in the midto lower crust of the Song- pan-Ganze and Sichuan-Yunnan blocks. In contrast, a high P-wave velocity (high-Vp) anomaly is resolved in the middle and lower crust beneath the Sichuan Basin. Our tomographic results provide seismic evidence for a dynamic model of lower crustal flow. Ongoing lower crustal flow beneath the central and eastern Tibetan Plateau abuts against the mechanically strong Si- chuan Basin resulting in accumulated strain in the Longmen Shan region. When a critical accumulation of strain energy was reached, its sudden release led to the occurrence of 2008 Wenchuan earthquake. Pronounced low-Vp anomalies are observed in the uppermost mantle in the region south of ~26°N. Combining these results with shear-wave splitting investigations, we suggest that the flow of asthenospheric material has impacted the velocity structure of the uppermost mantle and caused the thinning of the southwestern Yangtze Craton.
We used 71670 P-wave arrival times from 3594 earthquakes recorded by the Sichuan and Yunnan seismic networks to determine the three-dimensional P-wave velocity structure in the crust and uppermost mantle beneath the southeastern Tibetan Plateau. Our results show that prominent low P-wave velocity (low-Vp) anomalies exist in the midto lower crust of the Song- pan-Ganze and Sichuan-Yunnan blocks. In contrast, a high P-wave velocity (high-Vp) anomaly is resolved in the middle and lower crust beneath the Sichuan Basin. Our tomographic results provide seismic evidence for a dynamic model of lower crustal flow. Ongoing lower crustal flow beneath the central and eastern Tibetan Plateau abuts against the mechanically strong Si- chuan Basin resulting in accumulated strain in the Longmen Shan region. When a critical accumulation of strain energy was reached, its sudden release led to the occurrence of 2008 Wenchuan earthquake. Pronounced low-Vp anomalies are observed in the uppermost mantle in the region south of ~26°N. Combining these results with shear-wave splitting investigations, we suggest that the flow of asthenospheric material has impacted the velocity structure of the uppermost mantle and caused the thinning of the southwestern Yangtze Craton.
基金
supported by Chinese Academy of Sciences (Grant No. KZCZ-YW-134)
National Natural Science Foundation of China (Grant No. 90814014)
