苏鲁地区剪切波速度结构研究及与地震关系探讨
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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800km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150km深度下出现高速层,反映扬子板块的俯冲深度为100km以下,俯冲板片厚度在100km以上;板片拆离下沉深度甚至达到300km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。
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 structures 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 km, 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 focals 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.
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 structures 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 km, 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 focals 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.
引文
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[4]金振民,金淑燕,高山,等.大别山超高压岩石形成深度局限于100～150km吗?———针状含钛铬磁铁矿的发现及其动力学意义的思考[J].科学通报,1998,43(7):767～770.
[5]刘福田,徐佩芬,刘劲松,等.大陆深俯冲带的地壳速度结构—东大别造山带深地震宽角反射/折射研究[J].地球物理学报,2003,46(3):366-372.
[6]杨文采,佘长青.根据地球物理资料分析大别-苏鲁超高压变质带演化的运动学与动力学[J].地球物理学报,2001,44(3):346-359.
[7]王椿镛,张先康,陈步云,等.大别造山带的地壳结构研究[J].中国科学(D),1997,27:221-226.
[8]张学民.利用S波波形拟合反演台站下方剪切波速度结构的方法研究[D],合肥:中国科技大学地球物理与空间科学系,2001.
[9]ZhangXM,ShuPY,LiYM,etal.Astudyontransversal wavevelocitystructureunderseismicstationbyinputtingpureS wave[J].ChineseJournalofGeophysics,2002,45(1):67-75.
[10]纪晨,姚振兴.用于地球物理反演的均匀设计优化算法[J].地球物理学报,1996,39(2):233-242.
[11]杨文采,程振炎,陈国九,等.苏鲁超高压变质带北部地球物理调查(Ⅰ)—深反射地震[J].地球物理学报,1999,42(1):41-51.
[12]卢造郧,蒋秀琴,白云,等.胶辽渤海地区地壳上地幔结构特征与介质的横向非均匀性[J].华北地震科学,1999,17(2):43-51.
[13]刘昌铨,刘光夏,杜官恒.郯庐古裂谷中段地壳结构的初步研究—二维动力学射线追踪方法的解释结果[J].华北地震科学,1987,5(2):1-12.
[14]孙若昧,赵燕来,吴丹.京津唐地区地壳结构与强震的发生—Ⅱ.S波速度结构[J],地球物理学报,1996,39(3):347-355.
[15]徐佩芬,孙若昧,刘福田,等.扬子板块俯冲、断离的地震层析成像证据[J].科学通报,1999,44(15):1658-1661.
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