伽师强震群区震源细结构的深地震反射探测研究
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摘要
穿过伽师强震群的深地震反射剖面提供了研究区从地表直至莫霍界面的地壳细结构图像.探测结果表明:研究区上、下地壳分界面埋深约20~30 km,莫霍界面埋深约52~58 km.上地壳内部存在着两种截然不同的反射图像.上地壳上部为沉积盖层,厚度约8~9 km,盖层内部反射成层分布,显示了稳定而连续的沉积特点;上地壳下部则为“反射透明”背景下存在的叠层状反射带.下地壳内部呈现明显的反射性质,具体体现在上、下地壳分界面和莫霍间断面都表现为具有一定持续时间的多循环反射叠层结构特征.时间剖面上所有反射事件由北东向南西下倾的整体图像直观地反映了塔里木盆地地壳变形而向西昆仑下插入的事实.剖面47km桩号附近,上地壳下部至壳幔过渡带以上地壳范围内存在一条高倾角的深断裂,具有走滑性质,本研究认为该深断裂与1997年伽师强震群的发生密切相关,推断它为伽师强震群的发震构造.而时间剖面上壳幔过渡带反射的连续性则说明该断裂没有向下穿过莫霍面.存在于上地壳上部的两条高倾角的浅部断层可能对应于地质推测的麦盖提—下苏洪断裂带,它们与位于其下方的地壳深断裂构成了伽师强震群可能的深、浅构造关系.
Deep seismic reflection profiling across Jiashi strong earthquake swarm region has revealed fine crustal images through to M-discontinuity of the studied area.The result shows that the boundary between the upper and lower crust in this area is about 20～30 km deep and M-discontinuity is about 52～58 km deep.Two completely different types of reflected images appear within the upper crust.The upper part of the upper crust is a stratified 8～9 km deep sedimentary cover,suggesting stable and continuous sedimentation,while the lower part of the upper crust oppears as a laminated reflecting layer against a background of "reflection transparency".The lower crust shows obvious reflectivity,characterized by multi-iteration laminated reflection of the boundary between the upper and lower crust as well as M-discontinuity.All the reflectors dipping downward from northeast to southwest on the CDP section visually reflect crustal deformation of Tarim Basin which thrusts downwards into west Kunlun Mts.Near post 47km there is a high dip angle fault stretching from the lower part of the upper crust to the top of the crust-mantle transitional zone.This strike-slip fault has a direct bearing on the occurrence of the Jiashi strong earthquake swarm and is an inferred causative fault for the swarm(1997) according to this study.However,the continuity of reflection from the crust-mantle transitional zone suggests that the fault does not stretch downwards to disrupt M-discontinuity.The two shallow faults with high dip angle in the upper part of the upper crust may correspond to the geologically inferred Markit-Xiasuhong fault zone.These two faults and the crustal fault below them jointly constitute a possible shallow-deep structure relationship for the Jiashi strong earthquake swarm.
Deep seismic reflection profiling across Jiashi strong earthquake swarm region has revealed fine crustal images through to M-discontinuity of the studied area.The result shows that the boundary between the upper and lower crust in this area is about 20～30 km deep and M-discontinuity is about 52～58 km deep.Two completely different types of reflected images appear within the upper crust.The upper part of the upper crust is a stratified 8～9 km deep sedimentary cover,suggesting stable and continuous sedimentation,while the lower part of the upper crust oppears as a laminated reflecting layer against a background of "reflection transparency".The lower crust shows obvious reflectivity,characterized by multi-iteration laminated reflection of the boundary between the upper and lower crust as well as M-discontinuity.All the reflectors dipping downward from northeast to southwest on the CDP section visually reflect crustal deformation of Tarim Basin which thrusts downwards into west Kunlun Mts.Near post 47km there is a high dip angle fault stretching from the lower part of the upper crust to the top of the crust-mantle transitional zone.This strike-slip fault has a direct bearing on the occurrence of the Jiashi strong earthquake swarm and is an inferred causative fault for the swarm(1997) according to this study.However,the continuity of reflection from the crust-mantle transitional zone suggests that the fault does not stretch downwards to disrupt M-discontinuity.The two shallow faults with high dip angle in the upper part of the upper crust may correspond to the geologically inferred Markit-Xiasuhong fault zone.These two faults and the crustal fault below them jointly constitute a possible shallow-deep structure relationship for the Jiashi strong earthquake swarm.
引文
[1]曲国胜,陈杰,陈新发等.伽师中强震震群成因及其未来地震危险性初探.见:中国地震局地质研究所编.地震危险性预测研究.北京:地震出版社,1998.158~168Qu G S,Chen J,Chen X F,et al.Primary study on the formation ofJiashi mid_strong earthquake swarm and future earthquake trend.In:Institute of Geology,CEA eds.The Study on the Prediction of theSeismic Risk(in Chinese),Beijing:Seismological Press,1998.158~168
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[5]段永红,赖晓玲,李松林等.新疆伽师地震的近场观测和对它的初步认识.地球物理学进展,1999,14(4):41~48Duan Y H,Lai X L,Li S L,et al.Near field earthquake observationof Jiashi and some deductions of Jiashi strong earthquake.Progress inGeophysics(in Chinese),1999,14(4):41~48
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[7]周仕勇,许忠淮.由震源谱推断1997年新疆伽师强震群破裂特征.地震学报,2000,22(2):113~124Zhou S Y,Xu Z H.Fracture characteristics of the 1997 Jiashi,Xinjiang,China,eartequake swarm inferred from source spectra.Acta Seismologica Sinica,2000,13(2):125~135
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[9]刘启元,陈九辉,李顺成等.新疆伽师强震群区三维地壳上地幔S波速度结构及其地震成因的探讨.地球物理学报,2000,43(3):356~365Liu Q Y,Chen J H,Li S C,et al.Passive seismic experiment inXinjiang_Jiashi strong earthquake region and discussion on its seismicgenesis.Chinese J.Geophys.(in Chinese),2000,43(3):356~365
[10]张先康,赵金仁,张成科等.帕米尔东北侧地壳结构研究.地球物理学报,2002,45(5):665~671Zhang X K,Zhao J R,Zhang C K,et al.Crustal structure at theNortheast side of the Pamirs.Chinese J.Geophys.(in Chinese),2002,45(5):665~671
[11]杨卓欣,赵金仁,张先康等.伽师强震群区上地壳三维速度层析成像.地震学报,2002,24(2):153~161Yang Z X,Zhao J R,Zhang X K,et al.Tomographic determinationof the upper crustal structure in the Jiashi strong earthquake swarmregion.Acta Seismologica Sinica,2002,15(2):162~170
[12]张云峰,王海涛,徐锡伟等.2003年2月24日新疆巴楚-伽师6.8级地震.国际地震动态,2003,291:1~10Zhang Y F,Wang H T,Xu X W,et al.The earthquake ofM6.8occurring in Bachu_Jiashi region,Xinjiang Uygur Autonomous regionon February 24,2003.Recent Development in World Seismology(inChinese),2003,291:1~10
[13]周仕勇,许忠淮,陈晓非.伽师强震群震源特征及震源机制力学成因分析.地球物理学报,2001,44(5):654~662Zhou S Y,Xu Z H,Chen X F.Analysis on the source characteristicsof the 1997 Jiashi swarm,Western China.Chinese J.Geophys.(inChinese),2001,44(5):654~662
[14]徐朝繁,张先康,段永红等.新疆伽师强震群区上部地壳细结构的高分辨折射地震探测研究.地震学报,2006,28(1):60~69Xu Z F,Zhang X K,Duan Y H,et al.Fine upper crustal structureof Jiashi strong earthquake swarm region in Xinjiang inferred fromhigh resolution seismic refraction profile data.Acta SeismologicaSinica,2006,19(1):62~71
[15]王椿镛,王贵美,林中洋等.用深地震反射方法研究邢台地震区地壳细结构.地球物理学报,1993,36(4):445~452Wang C Y,Wang G M,Lin Z Y,et al.A study on fine crustalstructure in Xingtai earthquake area based on deep seismic reflectionprofiling.Chinese J.Geophys.(Acta Geophysica Sinica)(inChinese),1993,36(4):445~452
[16]张先康,王椿镛,刘国栋等.延庆-怀来地区地壳细结构—利用深地震反射剖面.地球物理学报,1996,39(3):356~363Zhang X K,Wang C Y,Liu G D,et al.Fine crustal structure inYanqing_Huailai region by deep seismic reflection profiling.ChineseJ.Geophys.(Acta Geophysica Sinica)(in Chinese),1996,39(3):356~363
[17]Sandmeier K J,Wenzel F.Synthetic seismograms for a complexcrustal model.Geophys.Res.Lett.,1986,13:22~25
[2]王琪,丁国瑜,乔学军等.用GPS研究南天山(伽师)地区现今壳内变形,地震学报,2000,22(3):263~270Wang Q,Ding G Y,Qiao X J,et al.Research on present crustaldeformation in the southern Tianshan(Jiashi),China by GPSgeodesy.Acta Seismologica Sinica(in Chinese),2000,22(3):263~
[3]朱令仁,苏乃秦,杨马陵.1997年伽师强震群及三次成功的临震预报.中国地震,1998,14(2):101~115Zhu L R,Su N Q,Yang M L.Activity of the 1997 Jiashi strongswarm in Xinjiang and three successful impending predictions for it.Earthquake Research in China(in Chinese),1998,14(2):101~115
[4]杨欣,高国英.1997年伽师强震群序列特征和震源机制的初步研究.地震学报,1998,20(6):573~579Yang X,Gao G Y.A preliminary research on the characteristics andthe source mechanism of the Jiashi strong earthquake swarm.ActaSeismologica Sinica(in Chinese),1998,20(6):573~579
[5]段永红,赖晓玲,李松林等.新疆伽师地震的近场观测和对它的初步认识.地球物理学进展,1999,14(4):41~48Duan Y H,Lai X L,Li S L,et al.Near field earthquake observationof Jiashi and some deductions of Jiashi strong earthquake.Progress inGeophysics(in Chinese),1999,14(4):41~48
[6]周仕勇,许忠淮,韩京等.主地震定位法分析以及1997年新疆伽师强震群高精度定位.地震学报,1999,21(3):258~265Zhou S Y,Xu Z H,Han J,et al.Analysis on the master eventmethod and precise location of 1997 Jiashi strong earthquake swarm inwestern China.Acta Seismologica Sinica,1999,12(3):285~291
[7]周仕勇,许忠淮.由震源谱推断1997年新疆伽师强震群破裂特征.地震学报,2000,22(2):113~124Zhou S Y,Xu Z H.Fracture characteristics of the 1997 Jiashi,Xinjiang,China,eartequake swarm inferred from source spectra.Acta Seismologica Sinica,2000,13(2):125~135
[8]胥颐,刘福田,刘建华等.天山地震带的地壳结构与强震构造环境.地球物理学报,2000,43(2):184~193Xu Y,Liu F T,Liu J H,et al.Crustal structure and tectonicenvironment of strong earthquakes in the Tianshan earthquake belt.Chinese J.Geophys.(in Chinese),2000,43(2):184~193
[9]刘启元,陈九辉,李顺成等.新疆伽师强震群区三维地壳上地幔S波速度结构及其地震成因的探讨.地球物理学报,2000,43(3):356~365Liu Q Y,Chen J H,Li S C,et al.Passive seismic experiment inXinjiang_Jiashi strong earthquake region and discussion on its seismicgenesis.Chinese J.Geophys.(in Chinese),2000,43(3):356~365
[10]张先康,赵金仁,张成科等.帕米尔东北侧地壳结构研究.地球物理学报,2002,45(5):665~671Zhang X K,Zhao J R,Zhang C K,et al.Crustal structure at theNortheast side of the Pamirs.Chinese J.Geophys.(in Chinese),2002,45(5):665~671
[11]杨卓欣,赵金仁,张先康等.伽师强震群区上地壳三维速度层析成像.地震学报,2002,24(2):153~161Yang Z X,Zhao J R,Zhang X K,et al.Tomographic determinationof the upper crustal structure in the Jiashi strong earthquake swarmregion.Acta Seismologica Sinica,2002,15(2):162~170
[12]张云峰,王海涛,徐锡伟等.2003年2月24日新疆巴楚-伽师6.8级地震.国际地震动态,2003,291:1~10Zhang Y F,Wang H T,Xu X W,et al.The earthquake ofM6.8occurring in Bachu_Jiashi region,Xinjiang Uygur Autonomous regionon February 24,2003.Recent Development in World Seismology(inChinese),2003,291:1~10
[13]周仕勇,许忠淮,陈晓非.伽师强震群震源特征及震源机制力学成因分析.地球物理学报,2001,44(5):654~662Zhou S Y,Xu Z H,Chen X F.Analysis on the source characteristicsof the 1997 Jiashi swarm,Western China.Chinese J.Geophys.(inChinese),2001,44(5):654~662
[14]徐朝繁,张先康,段永红等.新疆伽师强震群区上部地壳细结构的高分辨折射地震探测研究.地震学报,2006,28(1):60~69Xu Z F,Zhang X K,Duan Y H,et al.Fine upper crustal structureof Jiashi strong earthquake swarm region in Xinjiang inferred fromhigh resolution seismic refraction profile data.Acta SeismologicaSinica,2006,19(1):62~71
[15]王椿镛,王贵美,林中洋等.用深地震反射方法研究邢台地震区地壳细结构.地球物理学报,1993,36(4):445~452Wang C Y,Wang G M,Lin Z Y,et al.A study on fine crustalstructure in Xingtai earthquake area based on deep seismic reflectionprofiling.Chinese J.Geophys.(Acta Geophysica Sinica)(inChinese),1993,36(4):445~452
[16]张先康,王椿镛,刘国栋等.延庆-怀来地区地壳细结构—利用深地震反射剖面.地球物理学报,1996,39(3):356~363Zhang X K,Wang C Y,Liu G D,et al.Fine crustal structure inYanqing_Huailai region by deep seismic reflection profiling.ChineseJ.Geophys.(Acta Geophysica Sinica)(in Chinese),1996,39(3):356~363
[17]Sandmeier K J,Wenzel F.Synthetic seismograms for a complexcrustal model.Geophys.Res.Lett.,1986,13:22~25
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