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利用云南、四川地震台网记录到的3594个地震事件的71670条P波到时资料反演求得青藏高原东南缘地壳和上地幔的三维P波速度结构.反演结果清晰地显示了川滇菱形块体以及松潘-甘孜块体在中、下地壳深度处低速异常显著,而四川盆地在该深度处以高速为主要特征,我们的成像结果为下地壳流模型提供了地震学方面的证据.下地壳流在受到坚硬的四川盆地的阻挡后,深部物质沿着龙门山断裂带向上逆冲推覆,导致应变在龙门山断裂带脆性地壳内高度积累,应变能在积累到一定程度后的突然释放导致了汶川地震的发生.在26°N以南地区的上地幔顶部低速异常明显,结合各向异性的研究成果,我们认为软流圈物质的流动影响了该区上地幔顶部的波速结构,并且软流圈热物质在长期的流动过程中造成了扬子克拉通在西南部的减薄.
The 3-D P wave velocity structures of the crust and upper mantle in the southeastern margin of the Qinghai-Tibet Plateau are obtained by using 71670 P wave arrival-time data of 3594 seismic events recorded by the Yunnan and Sichuan Seismological Networks. The inversion results clearly show that Sichuan- The diamond block and the Songpan-Ganzi block have significant low-velocity anomalies at the middle and lower crust depths, while the Sichuan Basin is characterized by high velocities at this depth. Our imaging results provide seismological evidence for the lower crustal flow model. After the blockade of the crustal flow blocked by the hard Sichuan Basin, the deep material thrusts upwards along the Longmen Shan fault zone, resulting in a high level of strain accumulation in the crustal crust of the Longmenshan fault zone. The sudden release of strain energy after a certain degree of accumulation Leading to the occurrence of the Wenchuan earthquake.At the top of the upper mantle in the area south of 26 ° N, the anomalous low-velocity anomalies are obvious. Based on the anisotropic research results, it is considered that the flow of asthenosphere material affects the velocity structure of the top of the upper mantle in this area The asthenospheric thermo-substance caused the thinning of the Yangtze craton in the southwest during the long-term flow.