第9卷第2期2012年3月CHINESEJOURNALOFENGINEERINGGEOPHYSICSVol.9,No.2Mar.,2012文章编号:1672—7940(201202—0175—09doi:10.3969/j.issn.1672-7940.2012.02.010纵波速度模型约束的首都圈地壳横波速度结构成像张智1,李良杰1,张艳瑾1,熊彬1,赵国敏2(1.桂林理工大学地球科学学院,广西桂林541004;2.天津市地震局,天津210003基金项目:国家自然科学基金(编号:40804017和40974077及41164004;国家科技专项项目(编号:SinoProbe-02-02-02联合资助。作者简介:张智(1975-,男,湖南衡阳人,主要从事地震波层析成像技术研究。E-mail:zhangzhi@glite.edu.cn摘要:通过搜集首都圈地震台网记录到的634个地震事件的近三万条地震射线,并从中挑选出274条信噪比高、发育良好的面波频散曲线,并将已有的纵波速度转换为横波速度,作为横波速度反演的初始模型,利用最小二乘反演方法进行面波频散层析成像,得到了研究区地壳S波速度结构和地壳的厚度分布以及一些初步结论:地壳可分为地表、基底、上地壳、中地壳、下地壳五层,中地壳整体横波速度表现为弱梯度,局部出现负速度梯度,下地壳横波速度均呈现不同程度的异常,证实了中地壳低速层的存在;研究区内速度存在明显横向不均匀性,这是复杂的地质构造特征在地球物理场中的响应;各构造单元表现明显不同的速度结构变化,中地壳层位速度变化范围较小;同一构造单元在不同深度的层位上速度变化明显,出现高低速异常交替现象,特别是在张渤断裂带上地壳层位以上,高速和低速异常块体交替明显;地壳平均厚度29~40km,并且从东南向西北逐渐变厚加深,其中张北地区地壳最厚达40km,华北裂陷盆地地壳厚度为29~32km,华北裂陷盆地中部的深浅交叉的异常块体内的冀中坳陷构造最薄。关键词:首都圈;面波反演;S波速度结构中图分类号:P631.4文献标识码:A收稿日期:2012-01-10CrustalS-WaveVelocityTomographyConstrainedbyP-WaveVelocityModelintheCapitalRegionZhangZhi1,LiLiangjie1,ZhangYanjin1,XiongBin1,ZhaoGuomin2(1.CollegeofEarthSciences,GuilinUniversityofTechnology,GuilinGuangxi541004,China;2.EarthquakeAdministratorofTianjinMunicipality,Tianjin210003,ChinaAbstract:Wepickedup274well-developedandhighsignaltonoiseperformancesurfacewaveray-pathsrecordedby38seismicstationsintheCapitalSeismicstationNetworkandstudythecrustoftheCapitalregionbysurfacewavetomographymethodthroughtheorigi-nalvelocitymodelfromPvelocitytransformation.Thenweobtain,analyzeandinterpretthedepthsectionandSwavevelocitystructure.Herearesomepreliminaryresults:firstly,theareacrustcouldbedividedintofivelayers:surface,basement,uppercrust,mid-crustandlowercrust.Themid-crustSvelocitystructureshowslowgradient,evennegativeve-locitygradientpartly,andSvelocityshowsdifferentdegreeanomalyinlowercrust.Sothis工程地球物理学报(ChineseJournalofEngineeringGeophysics第9卷furtherprovedthetruthofmid-crustexist.Secondly,Swavevelocityprofileshowsobvi-ouslateralheterogeneityintheCapitalregion,forthisistheresponseofthecomplexgeo-logicalstructuralcharacteristicinthegeophysicalfield;Everytectonicunitshowsobviousdifferentvelocitystructures,andthevelocitychangeslessinmid-crustlayer;thesametectonicunithascleardifferentvelocitychangesindifferentdepth,andthehighvelocityandlowvelocityalternateabnormally,particularly,abovethecrustlayerofthefaultzone.BecauseofZhangjiakou-bohaiseariftbrokenbelt,highervelocityandlowvelocityabnor-malblockalternateobviously.thirdly,thecrustaveragethicknessintheCapitalregionisfrom29to40kilometers,andpresentsthedistinguishingfeaturethatthethicknessmorethickeranddeeperfromsoutheasttonorthwest,themostthickareaisZhangbeiareaa-roundZhangjiakou,intheNorthChinariftdepressionbasin,thecrustthicknessisfrom29to32kilometers,andthemostthinplaceislocatedinNorthChinabasin.Keywo...