松潘—甘孜造山带地壳速度结构
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摘要
位于川西地区的奔子栏—唐克深地震测深剖面以NNE走向穿越松潘—甘孜造山带 .根据人工地震记录分析得到的震相走时和相关的振幅信息 ,确定了该剖面二维P波地壳速度结构 .剖面的地壳结构可分为 5层 ,其中第 1,2 ,3层为上地壳 ;第 4 ,5层为下地壳 .上地壳中部普遍存在低速异常带 ,但龙日坝以北 ,这一低速带与其上覆的低速基底合为一体 .同时 ,沿剖面的地壳速度结构具有较强的横向变化 .据此 ,可将剖面分为 4段 ,即甘孜—理塘断裂以南、甘孜—理塘断裂至鲜水河断裂、鲜水河断裂至龙日坝断裂和龙日坝断裂以北 .这与区域构造划分基本一致 .地壳厚度沿测线从南西向北东逐渐减薄 ,即从金沙江畔的 6 2km减小到黄河附近的 5 2km .根据PmP震相分析 ,莫霍界面深度在鲜水河断裂两侧没有明显变化 .全剖面的地壳平均速度较低 ,为 6 .30km/s.奔子栏—唐克剖面揭示了该地区的“造山带”型地壳上地幔结构特征 .鲜水河断裂带位于剖面的中部 ,该地区的上地壳速度为正异常 ,而下地壳和上地幔顶部存在负异常 .笔者认为 ,这是一类有利于强震孕育和发生的深部构造环境 .
The Benzilan-Tangke deep seismic sounding profile in the western Sichuan region passes through the Songpan-Garze orogenic belt with trend of NNE. Based on the travel times and the related amplitudes of phases in the record sections, the 2-D P-wave crustal structure was ascertained in this paper. The velocity structure has quite strong lateral variation along the profile. The crust is divided into 5 layers, where the first, second and third layer belong to the upper crust, the forth and fifth layer belong to the lower crust. The low velocity anomaly zone generally exists in the central part of the upper crust on the profile, and it integrates into the overlying low velocity basement in the area to the north of Ma′erkang. The crustal structure in the section can be divided into 4 parts: in the south of Garze-Litang fault, between Garze-Litang fault and Xianshuihe fault, between Xianshuihe fault and Longerba fault and in the north of Longerba fault, which are basically coincided with the regional tectonics division. The crustal thickness decreases from southwest to northeast along the profile, that is, from 62 km in the region of the Jinshajiang River to 52 km in the region of the Yellow River. The Moho discontinuity does not obviously change across the Xianshuihe fault based on the PmP phase analysis. The crustal average velocity along the profile is lower, about 6.30 km/s. The Benzilan-Tangke profile reveals that the crust in the study area is orogenic. The Xianshuihe Fault belt is located in the central part of the profile, and the velocity is positive anomaly on the upper crust, and negative anomaly on the lower crust and upper mantle. It is considered as a deep tectonic setting in favor of strong earthquake′s accumulation and occurrence.
The Benzilan-Tangke deep seismic sounding profile in the western Sichuan region passes through the Songpan-Garze orogenic belt with trend of NNE. Based on the travel times and the related amplitudes of phases in the record sections, the 2-D P-wave crustal structure was ascertained in this paper. The velocity structure has quite strong lateral variation along the profile. The crust is divided into 5 layers, where the first, second and third layer belong to the upper crust, the forth and fifth layer belong to the lower crust. The low velocity anomaly zone generally exists in the central part of the upper crust on the profile, and it integrates into the overlying low velocity basement in the area to the north of Ma′erkang. The crustal structure in the section can be divided into 4 parts: in the south of Garze-Litang fault, between Garze-Litang fault and Xianshuihe fault, between Xianshuihe fault and Longerba fault and in the north of Longerba fault, which are basically coincided with the regional tectonics division. The crustal thickness decreases from southwest to northeast along the profile, that is, from 62 km in the region of the Jinshajiang River to 52 km in the region of the Yellow River. The Moho discontinuity does not obviously change across the Xianshuihe fault based on the PmP phase analysis. The crustal average velocity along the profile is lower, about 6.30 km/s. The Benzilan-Tangke profile reveals that the crust in the study area is orogenic. The Xianshuihe Fault belt is located in the central part of the profile, and the velocity is positive anomaly on the upper crust, and negative anomaly on the lower crust and upper mantle. It is considered as a deep tectonic setting in favor of strong earthquake′s accumulation and occurrence.
引文
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HoleJA .1992.Nonlinearhigh resolutionthree dimensionalseismictraveltimetomography[J].JGeophysRes,97:6553～6562
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MeissnerR .1986.TheContinentalCrust[M ].London:AcademicPress,1～426
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ThurberCH .1983.Earthuakelocationsandthree dimensionalcrustalstructureintheCoyoteLakearea,centralCalifornia[J].JGeophysRes,88:8226～8236
VidaleJE .1988.Finite differencetraveltimecalculation[J].BullSeismSocAmer,78:2062～2076
崔作舟,陈纪平,吴苓.1996.阿尔泰—台湾岩石圈地学断面综合研究:花石峡—邵阳深部地壳的结构和构造[M ].北京:地质出版社,49～168
崔作舟,卢德源,陈纪平,等.1987.攀西地区的深部地壳结构与构造[J].地球物理学报,30(6):566～580
丁志峰,曾融生,吴大铭.1992.青藏高原的Pn波速度和Moho面的起伏[J].地震学报,14(增刊):592～599
阚荣举,张四昌,晏凤桐,等.1977.我国西南地区现代构造应力场与现代构造活动特征的探讨[J].地球物理学报,20(2):96～109
李坪.1993.鲜水河—小江断裂带[M ].北京:地震出版社,1～50
林中洋,胡鸿翔,张文彬,等.1993.滇西地区地壳上地幔速度结构特征的研究[J].地震学报,15(4):427～440
任纪舜,姜春发,张正坤,等.1980.中国大地构造及其演化[M ].北京:科学出版社,1～124
任纪舜,王作勋,陈炳蔚,等.1999.中国及邻区大地构造图[Z].北京:地质出版社
四川省地震局.1986.1981年道孚地震[M ].北京:地震出版社,33～52
四川省地震局.1989.鲜水河活动断裂带[M ].成都:四川科学技术出版社,1～20
王椿镛.1985.二维射线合成地震图的计算及平凉-渭南地震测深剖面的解释[J].地震研究,8(6):615～626
王椿镛,张先康,宋建立,等.1997.大别造山带地壳上部速度结构的有限差分成像[J].地球物理学报,40(4):495～502
王椿镛,MooneyWD ,王溪莉,等.2002.川滇地区的地壳上地幔三维速度结构研究[J].地震学报,24(1):1～16
王椿镛,吴建平,楼海,等.2003.青藏高原东缘的地壳P波速度结构[J].中国科学(待发表)
许志琴,侯立玮,王宗秀,等.1992.中国松潘—甘孜造山带的造山过程[M ].北京:地质出版社,1～60
熊绍柏,滕吉文,尹周勋,等.1986.攀西构造带南部地壳与上地幔结构的爆炸地震研究[J].地球物理学报,29(3):235～244
俞如龙,郝子文,侯立玮.1989.川西高原中新生代碰撞造山带的大地构造演化[J].四川地质学报,9(1):1～9
赵珠,张润生,刘茂林.1989.四川地区分区走时表的编制和检验[A].见:国家地震局科技监测司编.中国分区地震波走时表的研制[C].北京:地震出版社,21～50
朱文耀,程宗颐,熊永清,等.1997.利用GPS技术监测青藏高原地壳运动的初步结果[J].中国科学,27(5):385～389
AllenCR .1991.Fieldstudyofahighlyactivefaultzone:theXianshuihefaultofsouthwesternChina[J].GeolSocAmerBull,103:1178～1199
AmmonCJ ,VidaleJE .1993.Tomographywithoutrays[J].BullSeismSocAmer,83:509～528
CervenyV ,MolotkovIA ,PsencikI.1977.RayMethodinSeismology[M ].Prague:UniverzitaKarlova,1～214
CervenyV ,PsencikI.1984.SEIS83 numericalmodelingofseismicwavefieldin2Dlaterallyvaryinglayeredstructuresbytheraymethod[A].In:EngdahlERed.DocumentationofEarthquakeAlgorithm[C].BoulderColoRep:WorldDataCenterforSolidEarthGeophysics,SE 35,36～40
HoleJA .1992.Nonlinearhigh resolutionthree dimensionalseismictraveltimetomography[J].JGeophysRes,97:6553～6562
KingRW ,ShenF ,BurchfielBC ,etal.1997.GeodeticmeasurementofcrustalmotioninsouthwestChina[J].Geology,25:179～182
LarsonKM ,BurgmanR ,BilhamR ,etal.1999.KinematicsoftheIndiaEurasiacollisionzonefromGPSmeasurements[J].JGeophysRes,104:1077～1093
MeissnerR .1986.TheContinentalCrust[M ].London:AcademicPress,1～426
MooneyWD ,GinzburgA .1986.Seismicmeasurementsoftheinternalpropertyoffaultzone[J].PureApplGeophys,124:141～157
RoydenLH ,BurchfielBC ,KingRW ,etal.1997.SurfacedeformationandlowercrustalflowineasternTibet[J].Science,276:788～790
ThurberCH .1983.Earthuakelocationsandthree dimensionalcrustalstructureintheCoyoteLakearea,centralCalifornia[J].JGeophysRes,88:8226～8236
VidaleJE .1988.Finite differencetraveltimecalculation[J].BullSeismSocAmer,78:2062～2076
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