苏鲁地区剪切波速度结构研究及与地震关系探讨

Study on Shear Wave Velocity Structure beneath Jiangsu and Shandong Province and Its Relationship to Earthquakes

摘要:

利用S波纯波形拟合法以及T函数法反演了苏鲁地区壳幔剪切波速度结构,并利用长周期P波T函数反演得到了连云港和莱阳台下方800 km深度的速度结构.结果显示:(1)苏鲁地区大部分台站地壳表层及上地壳浅部速度偏高,分别对应高压、超高压物质和古老基底出露地区;(2)沿郯庐断裂带分布的台站均显示明显低速层,并具有北浅南深的特点;(3)连云港和莱阳台超深度反演结果显示两台均在150 km深度下出现高速层,反映扬子板块的俯冲深度为100 km以下,俯冲板片厚度在100 km以上;板片拆离下沉深度甚至达到300 km或者更深;(4)地震深度分布与低速层关系密切,沿郯庐断裂和烟台-五莲断裂的中小地震震源深度都比较深,有的甚至达到地壳的底部,反映这两条断裂目前切割深度都比较大,而且地幔物质相对比较活跃.

Abstract:

Using pure S waveform fitting and T function method, the shear wave velocity structures in crust and upper mantle under seismic stations in Jiangsu and Shandong province are obtained. By employing T function method on long-period P wave records, S wave velocity struc tures about 800 km deep are also inversed under Lianyungang and Laiyang stations. The results show that ： （ 1） the majority of stations in Jiangsu and Shandong province are located on where the shallow crust with high velocity, which is corresponding to the area with outcropping high-pressure and ultrahigh-pressure materials, and outcropping paleo-basement, respectively; （ 2） stations along Tancheng-Lujiang Fault present low velocity layers underneath, and the low velocity layer is deeper at south segment than that at north segment of the fault; （3） Great depth inversions under Lianyungang and Laiyang stations show that below the depth of 150 km both exhibits high velocity layer, which demonstrates that underthrust Yangtzi plate is under the depth of 100 km, with thickness of 100 kin, and delaminated slab can reach 300 km or deeper; （4） depth of earthquakes is closely related to the distribution of low velocity layers, along Tancheng-Lujiang and Yantai-wulian fault the locals are relatively deep, some even at the bottom of crust, which reflects that the cutting depth of two faults is larger and upper mantle there is active.