2003年青海德令哈6.7级地震序列的震源机制解及其构造含义
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摘要
利用8个流动数字地震台和国家数字地震台站的地震波形记录,测量了2003年4月17日青海德令哈6.7级地震及其主要余震的直达P波、SV波、SH波的初动方向和振幅比,应用Snoke(2003)的测定震源机制解的格点尝试法,测定出德令哈地震序列的48个2.4级以上地震的震源机制解.搜集分析了美国哈佛大学测定的德令哈6.7级主震和2004年二期地震活动中的7个地震的震源机制解.基于余震空间分布特征和对震源机制解特征的分析,讨论了德令哈地震序列的可能断层活动方式和地震的构造含义.结果表明,主震和大部分余震都是沿NWW—SEE走向的逆断层错动,北边的上盘可能沿低角度向北倾的断层面向南仰冲;个别正断层余震可能是震源区挤压变形弧顶区附近发生的局部张性破裂;在二期地震活动中,逆断层和走滑断层都有,走滑断层地震主要发生在震源区东侧.德令哈地震活动是青藏高原东北缘NWW—SEE向延伸的挤压带继续处于隆升活动中的表现,这一继承性新构造运动是德令哈地震序列的可能发震原因.
Using digital seismic records from 8 portable stations and from stations of National Digital Seismic Network,we have measured the polarities and amplitude ratios of direct P,SH and SV waves of 2003 Delingha,Qinghai,M6.7 earthquake and its aftershocks.Applying Snoke′s(2003) grid search algorithm we determined focal mechanism solutions of 48 M≥2.4 earthquakes.We also analyzed Harvard focal mechanism solutions of the Delingha mainshock and 7 late aftershocks.Our study result shows that the mainshock and most aftershocks have a reverse faulting mechanism with fault strike in NWW—SEE and the northern hanging wall moving southward and upward.Two normal faulting aftershocks may come from possible tensile fractures in front part of the compressive thrust arc.During the second phase of earthquake activity in 2004 the motion of main thrust fault might have induced rupture of some strike-slip faults in eastern part of the source region.The Delingha earthquakes are located in a wide NWW—SEE trend compression zone in northeastern Qinghai-Xizang plateau region,and the present-day uplift of this compression zone serves as the seismogenic origin of the Delingha earthquake sequence.
Using digital seismic records from 8 portable stations and from stations of National Digital Seismic Network,we have measured the polarities and amplitude ratios of direct P,SH and SV waves of 2003 Delingha,Qinghai,M6.7 earthquake and its aftershocks.Applying Snoke′s(2003) grid search algorithm we determined focal mechanism solutions of 48 M≥2.4 earthquakes.We also analyzed Harvard focal mechanism solutions of the Delingha mainshock and 7 late aftershocks.Our study result shows that the mainshock and most aftershocks have a reverse faulting mechanism with fault strike in NWW—SEE and the northern hanging wall moving southward and upward.Two normal faulting aftershocks may come from possible tensile fractures in front part of the compressive thrust arc.During the second phase of earthquake activity in 2004 the motion of main thrust fault might have induced rupture of some strike-slip faults in eastern part of the source region.The Delingha earthquakes are located in a wide NWW—SEE trend compression zone in northeastern Qinghai-Xizang plateau region,and the present-day uplift of this compression zone serves as the seismogenic origin of the Delingha earthquake sequence.
引文
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[10]Snoke J A.2003,FOCMEC:FOCal MEChanism Determinations.http://www.geol.vt.edu/outreach/vtso/focmec/.
[11]孙长虹,蔡德超,钱荣毅等.Snoke震源机制求解方法应用研究.地震地磁观测与研究,2010,31(4):7-13.Sun C H,Cai D C,Qian R Y,et al.An application of Snoke′salgorithm for focal mechanism determination.Seismol.Geomagnetic Obs.Res.(in Chinese),2010,31(4):7-13.
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[13]许忠淮.东亚地区现今构造应力图的编制.地震学报,2001,23(5):490-500.Xu Z H.A present-day tectonic stress map for eastern Asiaregion.Acta Seismologica Sinica(in Chinese),2001,23(5):490-500.
[14]万永革,沈正康,刁桂苓等.利用小震分布和区域应力场确定大震断层面参数方法及其在唐山地震序列中的应用.地球物理学报,2008,51(3):793-804.Wan Y G,Shen Z K,Diao G L,et al.An algorithm of faultparameter determination using distribution of smallearthquakes and parameters of regional stress field and itsapplication to Tangshan earthquake sequence.Chinese J.Geophys.(in Chinese),2008,51(3):793-804.
[15]许忠淮,汪素云,黄雨蕊等.由多个小震推断的青甘和川滇地区地壳应力场的方向特征.地球物理学报,1987,30(5):476-486.Xu Z H,Wang S Y,Huang Y R,et al.Directions of meanstress axes in southwestern China deduced from microearthquakedata.Chinese J.Geophys.(in Chinese),1987,30(5):476-486.
[16]Wan Y G.Comtemporary tectonic stress field in China.EarthquakeScience,2010,23(4):377-386.
[17]陈顒.地壳岩石的力学性能.北京:地震出版社,1988.Chen Y.Mechanic Property of Crustal Rocks(in Chinese).Beijing:Seismological Press,1988.
[18]虢顺民,江在森,张崇立.青藏高原东北缘晚第四纪块体划分与运动态势研究.地震地质,2000,22(3):219-231.Guo S M,Jiang Z S,Zhang S L.Division and motion statusof blocks for northeastern Tibetan plateau in late Quternary.Seismology and Geology(in Chinese),2000,22(3):219-231.
[2]吕坚,郑勇,倪四道等.2005年11月26日九江—瑞昌Ms5.7、Ms4.8地震的震源机制解与发震构造研究.地球物理学报,2008,51(1):162-168.LüJ,Zheng Y,Ni S D,et al.Focal mechanism andseismogenic structures of the Ms5.7 and Ms4.8 Jiujiang-Ruichang earthquakes of Nov.26,2005.Chinese J.Geophys.(in Chinese),2008,51(1):162-168.
[3]郑勇,马宏生,吕坚.汶川地震强余震(Ms≥5.6)的震源机制解及其与发震构造的关系.中国科学(D辑),2009,(4):23-36.Zheng Y,Ma H S,LüJ.Focal mechanism solutions ofMs≥5.6aftershocks of the Wenchuan earthquake and theirrelation with seismogenic structure.Science in China(SeriesD)(in Chinese),2009,(4):23-36.
[4]龙思胜.2001年四川雅江6.0级地震序列的破裂特征及发震构造.中国地震,2004,20(1):1-11.Long S S.Fracture characters and statutory of the Yajiangearthquake sequence with Ms6.0in the Sichuan region in2001.Earthquake Research in China(in Chinese),2004,20(1):1-11.
[5]Ratchkovski N A,Wiemer S,Hansen R A.Seismotectonicsof the Central Denali Fault,Alaska,and the 2002 DenaliFault earthquake sequence.Bull.Seis.Soc.Am.,2004,94(6B):S156-S174.
[6]Waldhauser F.HypoDD-A program to compute double-difference hypocenter locations.U.S.Geological SurveyOpen-File Report 01-113,2001.
[7]孙长虹,钱荣毅,肖国林等.2003年青海德令哈6.7级地震序列的重新定位和发震构造.物探与化探,2006,30(1):79-82.Sun C H,Qian R Y,Xiao G L,et al.The relocation andseismogenic structure of the Delingha earthquake sequence of2003in Qinghai.Geophys.Geochem.Explor.(in Chinese),2006,30(1):79-82.
[8]Rivers W,Wagner R.Geotool Version 4.0.0Manual,2005.
[9]Snoke J A.CLYDE and the Gopher:apreliminary analysis ofthe 12May 1990Sakhalin Island event.Seism.Res.Lett.,1990,61(3-4):161.
[10]Snoke J A.2003,FOCMEC:FOCal MEChanism Determinations.http://www.geol.vt.edu/outreach/vtso/focmec/.
[11]孙长虹,蔡德超,钱荣毅等.Snoke震源机制求解方法应用研究.地震地磁观测与研究,2010,31(4):7-13.Sun C H,Cai D C,Qian R Y,et al.An application of Snoke′salgorithm for focal mechanism determination.Seismol.Geomagnetic Obs.Res.(in Chinese),2010,31(4):7-13.
[12]俞春泉,陶开,崔效锋等.用格点尝试法求解P波初动震源机制解及解的质量评价.地球物理学报,2009,52(5):1402-1411.Yu C Q,Tao K,Cui X F,et al.P-wave first-motion focalmechanism solutions and their quality evaluation.Chinese J.Geophys.(in Chinese),2009,52(5):1402-1411.
[13]许忠淮.东亚地区现今构造应力图的编制.地震学报,2001,23(5):490-500.Xu Z H.A present-day tectonic stress map for eastern Asiaregion.Acta Seismologica Sinica(in Chinese),2001,23(5):490-500.
[14]万永革,沈正康,刁桂苓等.利用小震分布和区域应力场确定大震断层面参数方法及其在唐山地震序列中的应用.地球物理学报,2008,51(3):793-804.Wan Y G,Shen Z K,Diao G L,et al.An algorithm of faultparameter determination using distribution of smallearthquakes and parameters of regional stress field and itsapplication to Tangshan earthquake sequence.Chinese J.Geophys.(in Chinese),2008,51(3):793-804.
[15]许忠淮,汪素云,黄雨蕊等.由多个小震推断的青甘和川滇地区地壳应力场的方向特征.地球物理学报,1987,30(5):476-486.Xu Z H,Wang S Y,Huang Y R,et al.Directions of meanstress axes in southwestern China deduced from microearthquakedata.Chinese J.Geophys.(in Chinese),1987,30(5):476-486.
[16]Wan Y G.Comtemporary tectonic stress field in China.EarthquakeScience,2010,23(4):377-386.
[17]陈顒.地壳岩石的力学性能.北京:地震出版社,1988.Chen Y.Mechanic Property of Crustal Rocks(in Chinese).Beijing:Seismological Press,1988.
[18]虢顺民,江在森,张崇立.青藏高原东北缘晚第四纪块体划分与运动态势研究.地震地质,2000,22(3):219-231.Guo S M,Jiang Z S,Zhang S L.Division and motion statusof blocks for northeastern Tibetan plateau in late Quternary.Seismology and Geology(in Chinese),2000,22(3):219-231.
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