Tomographic Imaging of P and S Wave Velocity Structures Beneath North China and its Vicinity
Tomographic Imaging of P and S Wave Velocity Structures Beneath North China and its Vicinity
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发表时间：
2008
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通讯作者：
Wang Zhi-shuo;Wang Chun-yong
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作者：
Wang Zhi-shuo;Wang Chun-yong
利用华北及邻区475个地震台站的区域走时资料，反演了地壳和上地幔的P、S速度结构，采用伪弯曲射线追踪算法计算走时，用LSQR算法求解大型稀疏观测方程组，通过棋盘格检验，得到了华北地区地壳和上地幔的P、S速度结构。在水平方向网格尺寸为0.5° × 0.5 °，5个节点分别为1，10，25，扬子地块和中朝地块位于秦岭两侧，两块体速度结构的差异是中朝块体大部分地区存在低速异常，而扬子块体的速度分布为正态分布，表明扬子块体相对稳定，中朝块体仍处于活动状态，中朝块体速度结构的主要特征是：（如燕山隆起、太行山皮埃蒙特断裂带、郯庐断裂带、和秦岭-大别造山带）位于地壳和上地幔的低速区或低速区向高速区的过渡带，在唐山地震区，低速异常普遍存在于25 km、42 km和60 km深度，这可能意味着上地幔热物质向上流动，然后停止于上地壳下部。
The regional travel-time data from 475 seismic stations in the North China and its vicinity were used to inverse the P and S velocity structures of the crust and uppermost mantle.The pseudobending ray tracing algorithm was used to calculate the travel times.The large and sparse system of observation equations is solved by using the LSQR algorithm.According to the checker-board tests,reliable inversion results were obtained for a parameterized model with grid size of 0.5°by 0.5°in the horizontal directions and 5 nodes of 1,10,25,42 and 60 km in depth.The Yangtze Block and the Sino-Korean Block are located in two sides of the Qinling-Dabie orogenic belt.The differences of velocity structure between two Blocks are that lower velocity anomaly exists in most part of the Sino-Korean Block,while velocity distribution is normal in the Yangtze Block.This indicates that the Yangtze Block is relative stable,and the Sino-Korean Block is still active,where strong earthquakes have frequently occurred.Main features of the'velocity structure in the Sino-Korean Block are that major tectonic belts (such as Yanshan uplift,Taihangshan piedmont fault belt,Tanlu fault belt,and Qinling-Dabie orogenic belt)are located in the low velocity areas or the transition zone from low velocity area to high velocity area in the crust and upper mantle.In the Tangshan earthquake area,low velocity anomaly commonly exists at the depth of 25 km,42 km and 60 km,which may imply that the hot material in upper mantle upweUs,and then stops to the lower part of upper crust.