重复绝对重力测量观测的滇西地区和拉萨点的重力变化及其意义
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摘要
根据近年来在滇西地区和西藏拉萨绝对重力点上的一些新的绝对重力重复观测结果 ,对 1990年以来在这些点上绝对重力重复观测结果进行了分析 .滇西地区的 5个绝对重力观测点的近 10年的重复观测结果表明 ,大部分观测时段没有出现与地球动力学事件有关的重力变化 ,只有丽江和洱源 2个绝对重力观测点的观测结果显示丽江地震前后有变化 .为了研究该重力变化的原因 ,本文正演模拟了出现重力变化期间丽江地震同震位错引起的重力变化 ,模拟结果与实际观测结果有较好的一致性 .西藏拉萨近 10年以来的重复观测结果给出了拉萨点的绝对重力值以 - 1.82± 0 .9× 10 - 8m·s- 2 ·a- 1 速率下降 ,这从重力学的角度反映出青藏高原的隆升 .对拉萨点的重力变化机制进行了探讨 ,根据印度板块与欧亚大陆俯冲模型计算的拉萨点重力变化速率与观测到的重力变化速率较一致 ,表明现今拉萨地区重力变化是由于印度板块与欧亚大陆俯冲所引起 .根据印度板块向欧亚大陆俯冲的位错模型计算的拉萨点的重力变化与地表垂直位移的关系 ,将重力变化转换为拉萨点的隆升速率为 8.7mm a .
The observed results of repeated absolute gravity measurements since 1990 at the western Yunnan and at the Lhasa stations are analyzed, together with some new observed data at these stations. The repeated observation results during about 10 years at five stations in the western Yunnan indicate that no significant gravity changes related to the geodynamical events were observed in most observation epochs. Significant gravity changes have been detected at Lijiang and Eryuan stations in the western Yunnan before and after Lijiang earthquake ( M S=7.0). We modeled the gravity changes caused by the co seismic dislocation during the Lijiang earthquake, that are in good agreement with the observed data. The gravity changes with time about 10 years at Lhasa station have a slop of -1.82±0.9×10 -8 m·s -2 ·a -1 , indicating that Qinghai Xizang plateau has an uplift. The mechanisms of gravity changes at Lhasa were investigated. We calculated the gravity change rates based on the model of India plate to Eurasia subduction. The computed gravity change rate at Lhasa is ingood agreement with observed one, indicating that present gravity changes at Lhasa were caused by the India plate to Eurasia subduction. The Lhasa has an uplift of 8.7mm/a translated from gravity changes using computed ratio of the gravity changes to the vertical displacements from the dislocation model of the India plate to Eurasia subduction.
The observed results of repeated absolute gravity measurements since 1990 at the western Yunnan and at the Lhasa stations are analyzed, together with some new observed data at these stations. The repeated observation results during about 10 years at five stations in the western Yunnan indicate that no significant gravity changes related to the geodynamical events were observed in most observation epochs. Significant gravity changes have been detected at Lijiang and Eryuan stations in the western Yunnan before and after Lijiang earthquake ( M S=7.0). We modeled the gravity changes caused by the co seismic dislocation during the Lijiang earthquake, that are in good agreement with the observed data. The gravity changes with time about 10 years at Lhasa station have a slop of -1.82±0.9×10 -8 m·s -2 ·a -1 , indicating that Qinghai Xizang plateau has an uplift. The mechanisms of gravity changes at Lhasa were investigated. We calculated the gravity change rates based on the model of India plate to Eurasia subduction. The computed gravity change rate at Lhasa is ingood agreement with observed one, indicating that present gravity changes at Lhasa were caused by the India plate to Eurasia subduction. The Lhasa has an uplift of 8.7mm/a translated from gravity changes using computed ratio of the gravity changes to the vertical displacements from the dislocation model of the India plate to Eurasia subduction.
引文
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[2] HsuHT ,WangY ,ZhangWM .TestresultsofFG5112absolutegravimeteratWuhanstation.In:SegawaJetal.eds.BerlinHei delberg:SpringerVerlag.Gravity,GeoidandMarineGeodesy,1997,117,15～19
[3] OkuboS ,YoshidaS ,SatoT ,etal.VerifyingtheprecisionofanewgenerationabsolutegravimeterFG5Comparisonwithsuperconductinggravimetersanddectionofoceanicloadingtide.Geophys.Res.Lett.,1997,24:489～492
[4] WilliamsSDP ,BakerTF ,JeffriesG .AbsolutegravityMeasure mentsatUKtidegauges.Geophys.Res.Lett.,2001,28:2317～2320
[5] LambertA ,CourtierN .NewconstraintsonLaurentidepostglacialre boundfromabsolutegravitymeasurements.Geophys.Res.Lett.,2001,28:2109～2112
[6] TorgeW ,R derRH ,SchnllM,etal.Highprecisiongravitycon trolnetworkinYunnanChina1990Bur.Grav.Int.,Bull.d’Inf.,1990,67:118～127
[7] JIAMingyu,XINGCanfei,LIhui,etal.GravitychangeswithtimeinYunnanandBeijingobservedbyabsolutegravimetry.Bur.Grav.Int.,Bull.d’Inf.,1998,67:37～50
[8] TorgeW ,SchnllM,TimmenL ,etal.Absoluteandrelativegravimetry199019921995inthewesternYunnanearthquakepre dictionexperimentalarea.Mnchen:DeutscheGeod.Komm.,ReiheB ,1999,Nr.307,1～48
[9] 王 勇,许厚泽,张为民等.1996年中国中西部地区高精度绝对重力观测结果.地球物理学报,1998,41(6):818～825WangY ,XuHZ ,ZhangWM ,etal.ObservationalresultsofhighprecisionabsolutegravityincentralandwesternChinain1996.Chi neseJGeophys(inChinese),1998,41(6):818～825
[10] OkuboS .Gravityandpotentialchangesduetoshearandtensilefaultsinahalf space.J.Geophys.Res.,1992,97:7137～7144
[11] TanakaY ,OkuboS .Firstdetectionofabsolutegravitychangecausedbyearthquake.Geophy.Res.Lett.,2001,28:2929～2981
[12] 王绍晋,龙晓帆,罗淑进.丽江地震序列的震源机制、发震应力场和破裂特征.地震研究,1997,20(1):26～34WangSJ,LongXF ,LuoSJ.Thefocalmechanism,seismogenicstressfieldandreputurecharacteristicsoftheLijingearthquakese quence.J .Seis.Res.(inChinese),1997,20(1):26～34
[13] 徐 扬,菊地正辛,苏有锦.1996年2月3日云南丽江地震震源过程的体波反演.地震学报,1998,20(2):113～117XuY ,KikuchiM ,SuYJ.BodywaveforminversionforthesourceprocessoftheFebruary3,1996Lijiang,Yunnanearthquake.ActaSeis.Sinica(inChinese),1998,20(2):113～117
[14] 周光全,张建国,周瑞琦等.丽江7.0级地震的地震地质构造背景分析.地震研究,1997,20(1):92～100ZhouGQ ,ZhangJG ,ZhouRQ ,etal.AnalysisonseismologicaltectonicbackgroundoftheLijiangearthquake.J .Seis.Res.(inChinese),1997,20(1):92～100
[15] ZhaoS .JointinversionofobservedgravityandGPSbaselinechangesforthedetectionoftheactivefaultsegmentattheRedRiverfaultzone.Geophys.J .Int.,1995,122:70～88
[16] WangH .Effectsofglacialisostaticadjustmentsincethelatepleisto cencontheupliftoftheTibetPlateau.Geophys.J .Int.2001144:448～458
[17] ZhaoW ,NelsonKD ,INDEPTHProjectTeam.Deepseismicreflec tionevidenceforcontinentalunderthrustingbeneathsouthernTibet.Nature,1993,366:557～559
[18] MaZJ,ChenXl,YeSH ,etal..ContemporarycrustalmovementofcontinentalChinaobtainedbyglobalpositioningsystem(GPS)measurements.ChineseScienceBulletin,2001,48(18):1552～1554
[19] 许厚泽.青藏高原的大地测量研究.武汉:湖北科学技术出版社,2001XuHZ .GeodesyStudyoftheTibetanPlateau.Wuhan:HubeiSci enceandTechniquePress,2001
[20] LarsonK ,BurgmannR ,BilhamR ,etal.KinematicsoftheIndiaEurasiacollisionzonefromGPSmeasurements.J .Geophys.Res.,1999,104:1077～1093
[21] 王 勇,许厚泽.青藏高原印度板块向欧亚大陆俯冲速率的研究—GPS观测资料的反演结果.地球物理学报,2003,46(2):185～190WangY ,XuHZ .AstudyonConvergenceRateoftheIndiatoEur asiaSubductionBeneathTibetanPlateau.ChineseJGeophys(inChi nese),2003,46(2):185～190
[22] SavageJC .Localgravityanomaliesproducedbydislocationsources.J.Geophys.Res.,1984,89:1945～1952
[23] 董鸿闻,顾旦生,李国智等.中国大陆现今地壳垂直运动研究.西安:西安地图出版社,2002.132～149DongHW ,GuDS ,LiGZ ,etal.ResearchonVerticalRecentCrustalMovementoftheMainlandofChina.Xi’an:Xi’anCarto graphicPublishingHouse,2002.132～149
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