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利用适于地壳速度结构重建的有限差分反演技术和RayInvr技术,解释了下扬子地区符离集-奉贤地震测深剖面密集的宽角反射/折射地震资料,重建研究区地壳上地幔顶部P波速度结构.该剖面速度模型在纵向上大致可分上地壳、中地壳和下地壳三部分,横向上可划分为6个块体.研究区速度分布符合稳定地台的速度结构特征.上地壳总厚度10.5～13.0km,速度横向变化剧烈,底部速度可达到6.2km·s-1.中地壳下部及下地壳上部速度分布横向不均匀性显著.中地壳上部和下部、下地壳及上地幔顶部的P波速度值度值分别在5.9～6.2,6.3～6.4,6.6～7.0和8.06～8.30km·s-1左右.莫霍界面深度为30～36km.郯庐断裂带域两侧中上地壳速度结构明显不同,而下地壳未见明显的速度异常和界面形态异常显示.推测郯庐断裂嘉山段在中生代曾经切割整个地壳,后由于造山带伸展及壳内均衡作用等,使得断裂特征在弹性中上地壳中得以保留,而在粘塑性下地壳中的断裂迹象则逐渐消失.镇江附近5级以上地震与延伸至下地壳的深大断裂有关,其地震成因可能是来自岩石圈的能量容易沿深大断裂传输至中上地壳,在构造有利的位置积聚,最终诱发地震.
Using the finite-difference inversion and RayInvr techniques suitable for the reconstruction of the crustal velocity structure, the wide-angle reflection / refraction seismic data intensively interpreted by the Fuyu-Fengxian seismic profile in the Lower Yangtze region are interpreted to reconstruct the P wave at the top of the crust and upper mantle in the study area Velocity structure.The velocity model can be roughly divided into upper crust, middle crust and lower crust in the longitudinal direction and divided into 6 blocks laterally.The velocity distribution in the study area is consistent with the velocity structure characteristics of the stable platform.The upper crustal total The thickness is 10.5 ~ 13.0km, the lateral velocity changes drastically, and the bottom velocity can reach 6.2km · s-1. There is significant lateral heterogeneity in the velocity distribution in the lower crust and the lower crust.The upper and lower crust, the lower crust and the top of the upper mantle The values of P-wave velocities are about 5.9-6.2,6.3-6.4,6.6-7.0 and 8.06-8.30km · s-1, respectively, and the depth of Moho interface is about 30-36 km. The mid-upper crustal velocity on both sides of Tanlu fault zone The structure is obviously different, but there is no obvious velocity anomaly and interface morphology anomalies in the lower crust.It is presumed that the Jia-Shan segment of Tan-Lu fault had cut the whole crust in the Mesozoic, and then fracture due to extension of the orogenic belt and intra-crustal balance The sign is retained in the elastic upper middle crust, while the fracture in the lower crust of the viscoplasticity gradually disappears.The earthquakes above the magnitude of 5 in Zhenjiang are related to deep faults extended to the lower crust, and the possible causes of the earthquake may be from the lithosphere Energy is easily transported along the deep and large faults to the middle and upper crust, accumulating in favorable locations and eventually inducing earthquakes.