云南遮放—宾川和孟连—马龙宽角地震剖面的层析成像研究
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摘要
依据有限差分反演和射线反演的方法 ,利用走时、振幅比和重力布格异常数据对云南地区遮放—宾川和孟连—马龙宽角地震剖面的地壳上地幔结构进行层析成像研究 .遮放—宾川测线地壳厚度为 35～ 4 6km ,孟连—马龙测线地壳厚度 33～ 4 4 .5km .局部位置上地幔顶部P波速度值偏低 ,速度值变化范围大 ,反映出云南地区是典型的构造活动区的特点 .地壳上地幔结构存在一定程度的深浅构造一致性 ,意味着浅部物质活动存在深部背景 .遮放—宾川剖面速度结构显示地表怒江断裂东侧存在贯穿地壳的大规模低速异常 ,可能与深部物质上涌活动有关 .遮放—宾川线和孟连—马龙线速度结构显示作为一级构造单元分界线的红河断裂是超壳断裂 ,怒江断裂深及上地幔 .而昌宁—双江断裂显示为低角度铲式断层 ,意味着该断裂切割并不深 .云南地区强震的发生往往与延伸到上地幔的深大断裂有关 ,且一些浅源地震经常位于中上地壳深大断裂与其他断裂的交汇部位、高速块体与低速块体接触带上速度等值线弯曲的位置 .推测这样的位置有利于能量和区域应力的积累 .
Based on the finite difference inversion and ray inversion method, the crust and upper mantle's structure on the Zhefang—Binchuan and Menglian—Malong wide-angle seismic profiles, both of which are located in Yunnan province,are tomographyed using the geophysical data of travel-time, amplitude ratio and Bouger anomaly. Thus some new recognitions about the geodynamics and the seismotectonic environment are derived. The crustal thickness of the Zhefang—Binchuan profile is 35～46km,and that of the Menglian—Malong profile is 33～44.5km. The geometry of the Moho interface is like that given by Hu Hongxiang. The P wave velocity on the top of the mantle of some places is relatively low and the fluctuating range of the velocity is very large, which may indicates that the Yunnan region is a typical tectonic active area. Moreover, there exits a prominent consistency between the shallow and deep structures, which implys that the activity of shallow material always has a deep background. The velocity structure of the Zhefang—Binchuan profile indicates that there exists a large low velocity anomaly across the crust to the east of the Nujiang fault exposed on the ground,and this maybe related with the deep material upwelling. The characteristic of the large faults which are the borders between some first order tectonic units can also be derived by both of the velocity structure profiles: the Honghe fault is a super-fault that cut the lithosphere,the Nujiang fault cuts deeply in the crust and even stretches downward into the top of the upper mantle, yet the Changning—Shuangjiang fault has a listric shape with a small dip angle, which may suggest that its incision depth is not very deep. The large earthquakes in Yunnan province always have a relationship with the large and deep faults that stretch into the upper mantle. Some earthquakes with shallow focal depths are generally located at converge positions of faults within the upper and middle crust or the positions where the velocity contours on the belt between the high and low velocity anomaly blocks are crooked. It is inferred estimated that these locations are prone to the accumulation of the energy and the regional stress.
Based on the finite difference inversion and ray inversion method, the crust and upper mantle's structure on the Zhefang—Binchuan and Menglian—Malong wide-angle seismic profiles, both of which are located in Yunnan province,are tomographyed using the geophysical data of travel-time, amplitude ratio and Bouger anomaly. Thus some new recognitions about the geodynamics and the seismotectonic environment are derived. The crustal thickness of the Zhefang—Binchuan profile is 35～46km,and that of the Menglian—Malong profile is 33～44.5km. The geometry of the Moho interface is like that given by Hu Hongxiang. The P wave velocity on the top of the mantle of some places is relatively low and the fluctuating range of the velocity is very large, which may indicates that the Yunnan region is a typical tectonic active area. Moreover, there exits a prominent consistency between the shallow and deep structures, which implys that the activity of shallow material always has a deep background. The velocity structure of the Zhefang—Binchuan profile indicates that there exists a large low velocity anomaly across the crust to the east of the Nujiang fault exposed on the ground,and this maybe related with the deep material upwelling. The characteristic of the large faults which are the borders between some first order tectonic units can also be derived by both of the velocity structure profiles: the Honghe fault is a super-fault that cut the lithosphere,the Nujiang fault cuts deeply in the crust and even stretches downward into the top of the upper mantle, yet the Changning—Shuangjiang fault has a listric shape with a small dip angle, which may suggest that its incision depth is not very deep. The large earthquakes in Yunnan province always have a relationship with the large and deep faults that stretch into the upper mantle. Some earthquakes with shallow focal depths are generally located at converge positions of faults within the upper and middle crust or the positions where the velocity contours on the belt between the high and low velocity anomaly blocks are crooked. It is inferred estimated that these locations are prone to the accumulation of the energy and the regional stress.
引文
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[22] LudwingWJ ,NafeJE ,Drake
[2] 陈学波,李金森,赵静娴等.三江构造带基底构造特征与强震活动关系.见:陈运泰,阚荣举,滕吉文主编,中国固体地球物理学进展.北京:海洋出版社,1994.41～54ChenXB ,LiJS ,ZhaoJX ,etal.Thebasementstructuralcharac teristicsofSanjiangstructurebeltanditsrelationshipwithstrongearthquakes,In:ChenYTetal.ed.AdvancesinSolidEarthGeo physicsinChina.Beijing:OceanPress,1994.41～54
[3] 胡鸿翔,陆涵行,王椿镛等.云南地区地壳结构的爆破地震研究.地球物理学报,1986,29(2):133～144HuHX ,LuHX ,WangCY ,etal.ExplosioninvestigationofthecrustalstructureinWesternYunnanProvince.ChineseJ .Geophys.(ActaGeophysicaSinica)(inChinese),1986,29(2):133～144
[4] 胡鸿翔,高世玉.云南地区地壳浅部基底速度细结构的研究.中国地震,1993,19(4):356～363HuHX ,GaoSY .Theinvestigationoffinevelocitystructureofthebasementlayerofearth’scrustinwesternYunnanregion.EarthquakeResearchinChina(inChinese),1993,19(4):356～363
[5] 胡鸿翔,李学清.云南地区孟连—思茅—马龙剖面的基底速度系结构.见:陈运泰等主编,中国固体地球物理学进展.北京:海洋出版社,1994.100～106HuHX ,LiXQ .ThefinevelocitystructureofthebasementlayerofMenglianSimaoMalongprofileinYunnanregion.In:ChenYT ,ed in chief.AdvancesinSolidEarthGeophysicsinChina.Beijing:OceanPress,1994.100～106
[6] 阚荣举,林中洋.云南地壳上地幔构造的初步研究.中国地震,1986,2(4):50～61KanRJ,LinZY .ApreliminarystudyoncrustalanduppermantlestructureinYunnan.EarthquakeResearchinChina(inChinese),1986,2(4):50～61
[7] 阚荣举,赵晋明.腾冲火山地区的壳幔构造.见:陈运泰等主编,中国固体地球物理学进展.北京:海洋出版社,1994.23～30KanRJ ,ZhaoJM .Crust mantlestructureofTengchongvolcanicar ea.In:ChenYTed in chief.AdvancesinSolidEarthGeophysicsinChina.Beijing:OceanPress,1994.23～30
[8] KanRong ju,HuHong xiang,ZengRong sheng,etal.CrustalstructureofYunnanProvince,People’sRepublicofChina,fromseis micrefractionprofiles.Science,1986,234:433～437
[9] 王椿镛,张先康,丁志峰等.大别造山带上部地壳结构的有限差分层析成像.地球物理学报,1997,40(4):496～501WangCY ,ZhangXK ,DingZF ,etal.TomograhyfortheuppercrustalstrctureofDabieshanorogenicbeltusingfinitedifferencemeth od.ChineseJ.Geophys.(ActaGeophysicaSinica),1997,40(4):496～501
[10] 王椿镛,楼海,吴建平等.腾冲火山地热区地壳结构的地震学研究.地震学报,2002,24(3):231～242WangCY ,LouH ,WuJP ,etal.SeismologicalstudyonthecrustalstructureofTengchongvolcano geothermalarea.ActaSeismologicaSinica(inChinese),2002,24(3):231～242
[11] VidaleJE .Finite differencetraveltimecalculation.BullSeismSoc.Am,1988,78:2062～2076
[12] VidaleJE .Finite differencecalculationoftraveltimesinthreedimen tions.Geophys.,1990,55:521～526
[13] ZeltCA ,SmithRB .Scismictraveltimeinversionfor2Dcrustalve locitystructure.Geophys.J .Int.,1992,108:16～34
[14] GormanAR ,ClowesRM ,Atwo dimensionalinterpretationoftheplatformalArcheanlithosphereofwesternNorthAmerica.EOS .Trans.,1998,79:560
[15] ZeltCA ,ForsythDA .Modelingwide angleseismicdataforcrustalstructure:SoutheasternGrenvilleProvince.J .Geophys.Res.,1994,99(B6):11687～11704
[16] ZeltCA ,WhiteDJ.Crustalstructureandtectonicsofthesouthea sternCanadianCordillera.J.Geophys.Res.,1995,100:24255～24273
[17] ZeltCA .Modellingstragiesandmodelassessmentforwide angleseismictraveltimedata.GeophysJInt.,1999,139:183～204
[18] 陈炳蔚,王铠元,刘万熹等.怒江—澜沧江—金沙江地区大地构造.北京:地质出版社,1987.204ChenBW ,WangKY ,LiuWX ,etal.GeotectonicsinNujiang—Lanchangjiang—JingshajiangRegion(inChinese).Beijing:Geologi calPublishingHouse,1987.204
[19] JiangCS .VolcanoesandearthquakesinTengchongarea,Yunnanprovince,China.J.Seism.Res.,1985,8:107～120
[20] 马杏垣等.中国岩石圈动力学图集.北京:中国地图出版社,1989.38MaXY ,etal.LithosphericDynamicsAtlasofChina.Beijing:Car tographicPublishingHouse,1989.38
[21] YanQZ ,ZhangGQ ,KanRJ,etal.ThecruststructureofSimaotoMalongProfile,YunnanProvince,China.JournalofSeismologicalResearch(inChinese),1985,8(2):249～264
[22] LudwingWJ ,NafeJE ,Drake
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