The average upper mantle P wave velocity structure and lateral heterogeneity in the northern part of China and Mongolia are investigated by waveform inversion of broadband body waveform data recorded by CDSN and digit...The average upper mantle P wave velocity structure and lateral heterogeneity in the northern part of China and Mongolia are investigated by waveform inversion of broadband body waveform data recorded by CDSN and digital stations around China. The average model has a low P wave velocity lid (about 7.8～8.0 km·s -1 ) with thickness about 60 km, and two discontinuities with velocity jumps of 0.29 km·s -1 and 0.55 km·s -1 at depth of 410 km and 665 km respectively. In the Jungger basin, the P wave velocity of uppermost mantle is about 7.7 km·s -1 . The lid thickness (90～100 km) and velocity gradient (average gradient is greater than 0.005 5/s) are large. At the depth of 140 km the P wave velocity reaches to 8.2 km·s -1 . Near in Baikal, the lid is about 30 km thick with average P wave velocity of 8.00～8.05 km·s -1 .展开更多
In this study,on the basis of absolute first-arrival times of 84756 P-and S-waves from 6085 earthquakes recorded at 56 fixed stations in Yibin and surrounding areas in China from January 2009 to January 2019,focal par...In this study,on the basis of absolute first-arrival times of 84756 P-and S-waves from 6085 earthquakes recorded at 56 fixed stations in Yibin and surrounding areas in China from January 2009 to January 2019,focal parameters and three-dimensional(3 D)body-wave high-resolution velocity structures at depths of 0–30 km were retrieved by double-difference tomography.Results show that there is a good correspondence between the spatial distribution of the relocated earthquakes and velocity structures,which were concentrated mainly in the high-velocity-anomaly region or edge of high-velocity region.Velocity structure of P-and S-waves in the Yibin area clearly shows lateral inhomogeneity.The distribution characteristics of the P-and S-waves near the surface are closely related to the geomorphology and geologic structure.The low-velocity anomaly appears at the depth of 15–25 km,which is affected by the lower crust current.The Junlian–Gongxian and Gongxian–Changning earthquake areas,which are the two most earthquake-prone areas in the Yibin region,clearly differ in earthquake distribution and tectonic characteristics.We analyzed the structural characteristics of the Junlian–Gongxian and Gongxian–Changning earthquake areas on the basis of the 3 D bodywave velocity structures in the Yibin region.We found that although most seismicity in the Yibin area is caused by fluid injection,the spatial position of seismicity is controlled by the velocity structures of the middle and upper crust and local geologic structure.Fine-scale 3 D velocity structures in the Yibin area provide important local reference information for further understanding the crustal medium,seismogenic structure,and seismicity.展开更多
文摘The average upper mantle P wave velocity structure and lateral heterogeneity in the northern part of China and Mongolia are investigated by waveform inversion of broadband body waveform data recorded by CDSN and digital stations around China. The average model has a low P wave velocity lid (about 7.8～8.0 km·s -1 ) with thickness about 60 km, and two discontinuities with velocity jumps of 0.29 km·s -1 and 0.55 km·s -1 at depth of 410 km and 665 km respectively. In the Jungger basin, the P wave velocity of uppermost mantle is about 7.7 km·s -1 . The lid thickness (90～100 km) and velocity gradient (average gradient is greater than 0.005 5/s) are large. At the depth of 140 km the P wave velocity reaches to 8.2 km·s -1 . Near in Baikal, the lid is about 30 km thick with average P wave velocity of 8.00～8.05 km·s -1 .
基金supported by the Research Project of Tianjin Earthquake Agency(No.yb201901)Seismic Regime Tracking Project of CEA(No.2019010127)Combination Project with Monitoring,Prediction and Scientific Research of Earthquake Technology,CEA(No.3JH-201901006)
文摘In this study,on the basis of absolute first-arrival times of 84756 P-and S-waves from 6085 earthquakes recorded at 56 fixed stations in Yibin and surrounding areas in China from January 2009 to January 2019,focal parameters and three-dimensional(3 D)body-wave high-resolution velocity structures at depths of 0–30 km were retrieved by double-difference tomography.Results show that there is a good correspondence between the spatial distribution of the relocated earthquakes and velocity structures,which were concentrated mainly in the high-velocity-anomaly region or edge of high-velocity region.Velocity structure of P-and S-waves in the Yibin area clearly shows lateral inhomogeneity.The distribution characteristics of the P-and S-waves near the surface are closely related to the geomorphology and geologic structure.The low-velocity anomaly appears at the depth of 15–25 km,which is affected by the lower crust current.The Junlian–Gongxian and Gongxian–Changning earthquake areas,which are the two most earthquake-prone areas in the Yibin region,clearly differ in earthquake distribution and tectonic characteristics.We analyzed the structural characteristics of the Junlian–Gongxian and Gongxian–Changning earthquake areas on the basis of the 3 D bodywave velocity structures in the Yibin region.We found that although most seismicity in the Yibin area is caused by fluid injection,the spatial position of seismicity is controlled by the velocity structures of the middle and upper crust and local geologic structure.Fine-scale 3 D velocity structures in the Yibin area provide important local reference information for further understanding the crustal medium,seismogenic structure,and seismicity.
