气枪探测资料对华北地区地壳低速带的约束
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摘要
地壳低速带是岩石圈中的力学软弱带,对地震的孕育有重要作用。人工探测和天然地震层析成像资料均表明,华北地区在不同深度上均存在低速带。为进一步对华北地区地壳低速带的特性进行约束,我们分析了在唐山地区进行大容量气枪震源探测所获得的高分辨率观测资料。分析中发现,该地区的地震记录具有如下主要特征:①直达波Pg视速度为6km/s,可以追踪到约70km;②Moho面反射波PmP从50km开始就以强势震相出现;③PmP震相在150km处比Pg震相约滞后2s。本文利用合成地震图,通过波形正演对观测数据进行拟合,结果表明,合成地震图不仅可以解释各种震相的走时,同时也能较好地反映PmP和Pg的相对振幅。模型结果显示:①该地区平均地壳厚度为33km;②在该地区上下地壳各存在一个低速层。通过分析热流和大地电磁测深资料,认为该地区上/下低速层可能分别是流体和热作用的结果。
The low velocity zone is a mechanical weak band in the crust,which plays an important role in breeding of earthquakes.Artifical detection and nature earthquake tomography both show that low velocity layers exist in different depths in North China.We analyzed the high-resolution data detected by large volume airgun source in North China in order to put further constraint on the properties of the low velocity layers there.We found the following main characteristics in airgun data:firstly,apparent velocity of the direct P-wave's is approximately 6km/s,which could be traced upto nearly 70km;secondly,the PmP phase which reflected from Moho begin to appear as strong phases from 50km;thirdly,the PmP phase at 150km is 2s lag of the Pg phase.All these features show that the low velocity layer exist in the crust in this area.We use synthetic seismograms to forward modeling waveform to fit the observed data.The results showed that synthetic seismograms can not only explain the travel time of various seismic phases,but also obtain the amplitude ratio of PmP and Pg.The results of our modeling include:① the average thickness of crust in this area is 33km;② there exists a low velocity layer in both the upper and lower crust in this region.By comparing the heat and magnetotelluric data,we conclude that the low velocity layers in the upper and lower crusts were caused by fluid and thermal effect respectively.
The low velocity zone is a mechanical weak band in the crust,which plays an important role in breeding of earthquakes.Artifical detection and nature earthquake tomography both show that low velocity layers exist in different depths in North China.We analyzed the high-resolution data detected by large volume airgun source in North China in order to put further constraint on the properties of the low velocity layers there.We found the following main characteristics in airgun data:firstly,apparent velocity of the direct P-wave's is approximately 6km/s,which could be traced upto nearly 70km;secondly,the PmP phase which reflected from Moho begin to appear as strong phases from 50km;thirdly,the PmP phase at 150km is 2s lag of the Pg phase.All these features show that the low velocity layer exist in the crust in this area.We use synthetic seismograms to forward modeling waveform to fit the observed data.The results showed that synthetic seismograms can not only explain the travel time of various seismic phases,but also obtain the amplitude ratio of PmP and Pg.The results of our modeling include:① the average thickness of crust in this area is 33km;② there exists a low velocity layer in both the upper and lower crust in this region.By comparing the heat and magnetotelluric data,we conclude that the low velocity layers in the upper and lower crusts were caused by fluid and thermal effect respectively.
引文
渡边俊树,1990,多薄层低速带对P波的影响,国外地质勘探技术,11,28～31。
顾功叙,1990,地球物理勘探基础,北京:地质出版社。
胡圣标、何丽娟、汪集旸,2001,中国大陆地区大地热流数据汇编,地球物理学报,44(5),611～626。
嘉世旭、刘昌铨,1995,华北地区人工地震测深真相与地壳结构研究,地震地质,17(2),97～105。
嘉世旭、张先康,2005华北不同构造块体地壳结构及其对比研究,地球物理学报,48(3),611～620。
嘉世旭、张成科、赵金仁等,2009,华北东北部裂陷盆地与燕山隆起地壳结构,地球物理学报,52(1),99～110。
林建民、王宝善、葛洪魁等,2008,大容量气枪震源特征及地震波传播的震相分析,地球物理学报,51(1),206～212。
汪一鹏、邓启东、朱世龙,1989,华北地区岩石圈动力学特征,中国岩石圈动力学地图集,59,北京:中国地图出版社。
王雪秋、孙建国,2002,地震勘探中的数据保真问题综述,海相油气地质,7(1),55～58。
徐煜坚、罗焕炎,1985,华北北部地区地质模型与强震迁移,108～228,北京:地震出版社。
谢小碧、郑天愉、姚振兴,1992,理论地震图计算方法,地球物理学报,35(6),790～801。
杨晓松、马瑾、张先进,2003,大陆壳内低速层成因综述,地质科技情报,22(2),35～41。
杨德义、彭苏萍、常锁亮,2003,地震勘探常规低速带调查方法应用中的问题探讨,物探与化探,27(5),387～389。
赵国泽、刘国栋、王家映,1986,北京-柏各庄剖面连续介质大地电磁反演解释,地震学报,8,179～190。
Rongjiang Wang,1999,A Simple Orthonormalization Method for Stable and Efficient Computation of Green’s Functions.Bulletin ofthe Seismological of America,89(3),733～741.
Kaye M S,1987,Elastic Wave Velocity Structure of the Crust and Upper Mantle Beneath the North China Basin.Journal ofGeophysical Research,92(B9),9327～9350.
Wang B and Niu F,2010,A broad660km discontinuity beneath northeast China reve-aled by dense regional seismic networks inChina,J Geophys Res,115,B06308,doi:10.1029/2009JB006608.
Zhao D,Kanamori H,Negishi H et al,1996,Tomography of the source area of the1995Kobe earthquake:Evidence for fluids atthe hypocenter?Science,274,1891～1894.
顾功叙,1990,地球物理勘探基础,北京:地质出版社。
胡圣标、何丽娟、汪集旸,2001,中国大陆地区大地热流数据汇编,地球物理学报,44(5),611～626。
嘉世旭、刘昌铨,1995,华北地区人工地震测深真相与地壳结构研究,地震地质,17(2),97～105。
嘉世旭、张先康,2005华北不同构造块体地壳结构及其对比研究,地球物理学报,48(3),611～620。
嘉世旭、张成科、赵金仁等,2009,华北东北部裂陷盆地与燕山隆起地壳结构,地球物理学报,52(1),99～110。
林建民、王宝善、葛洪魁等,2008,大容量气枪震源特征及地震波传播的震相分析,地球物理学报,51(1),206～212。
汪一鹏、邓启东、朱世龙,1989,华北地区岩石圈动力学特征,中国岩石圈动力学地图集,59,北京:中国地图出版社。
王雪秋、孙建国,2002,地震勘探中的数据保真问题综述,海相油气地质,7(1),55～58。
徐煜坚、罗焕炎,1985,华北北部地区地质模型与强震迁移,108～228,北京:地震出版社。
谢小碧、郑天愉、姚振兴,1992,理论地震图计算方法,地球物理学报,35(6),790～801。
杨晓松、马瑾、张先进,2003,大陆壳内低速层成因综述,地质科技情报,22(2),35～41。
杨德义、彭苏萍、常锁亮,2003,地震勘探常规低速带调查方法应用中的问题探讨,物探与化探,27(5),387～389。
赵国泽、刘国栋、王家映,1986,北京-柏各庄剖面连续介质大地电磁反演解释,地震学报,8,179～190。
Rongjiang Wang,1999,A Simple Orthonormalization Method for Stable and Efficient Computation of Green’s Functions.Bulletin ofthe Seismological of America,89(3),733～741.
Kaye M S,1987,Elastic Wave Velocity Structure of the Crust and Upper Mantle Beneath the North China Basin.Journal ofGeophysical Research,92(B9),9327～9350.
Wang B and Niu F,2010,A broad660km discontinuity beneath northeast China reve-aled by dense regional seismic networks inChina,J Geophys Res,115,B06308,doi:10.1029/2009JB006608.
Zhao D,Kanamori H,Negishi H et al,1996,Tomography of the source area of the1995Kobe earthquake:Evidence for fluids atthe hypocenter?Science,274,1891～1894.
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