2011年10月12日北京市石景山区M_L2.1地震近场加速度记录初步分析
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摘要
根据近场强震台加速度记录对2011年10月12日北京市石景山区ML2.1地震的加速度影响场进行了计算分析。同时使用了首都圈宽频带数字台站记录数据通过P波初动格点尝试法解算出该地震的震源机制解,并与加速度影响场进行对比研究。结果表明,此次地震加速度影响场水平向加速度高于垂直向;水平向峰值加速度分布区和加速度影响场高低速度过渡区总体呈EW向或NEE向分布,与震源机制解结果的两个节面走向较为一致;加速度衰减NS向快于EW向。本文研究结果可为强震或较大地震发生后快速判定震害影响场提供参考依据。
An earthquake with a magnitude(ML) of 2.1 occurred at 16:40 UTC,October 12,2011,in the Shijingshan district in Beijing with an epicenter at 39.95° N,116.16° E.Eleven near-field strong motion stations,located less than 20 km from the epicenter,clearly recorded temporal variation of acceleration during the earthquake.The largest value of peak ground acceleration in the east-west(EW) and north-south(NS) components,22.528 gal and 30.989 gal,respectively,were both recorded by station LSG,which is situated approximately 5.6 km from epicenter.The largest value of peak ground acceleration in the vertical component was 12.797 gal,recorded by station CCS at an epicenter distance of 2.2 km.We synthesized the horizontal component by EW and NS records and used Generic Mapping Tools(GMT) software to mesh and illustrate the influence of horizontal and vertical acceleration on the field contour map.The results show that generally,the value of the NS component is larger than that of the EW component,and the horizontal component is larger than the vertical.Moreover,the acceleration distribution and influence field contour map of the horizontal component shows that peak ground acceleration in the southern area is a low value and that in the northern area is high.In addition,the two regions are divided by a transition zone that strikes near east-west(EW) or NEE.We obtained the average peak ground value of three components at 1 s intervals from station records after the earthquake occurred,which we synthesized into horizontal and vertical components to illustrate temporal variations in the map produced by GMT.After analyzing the average value records and temporal variation map,we detected that the decay in the NS direction is faster than that in the EW direction and that decay is faster in the vertical component than that in the horizontal component.Excepting the near-field strong motion stations,23 Capital Circle broadband digital seismic stations recorded digital waveform data during the earthquake.We interpreted initial P-wave polarity from these records and employed grid-point test method to obtain the Focal Mechanism Solution of the event.Results indicate normal faulting dominant in the Beijing-Tianjin area.The best double couple solution of the event is 295°,39° and-74° for strike,dip and rake angel,respectively;those of the other nodal plane are 96°,53°,and-102° with a 13% inconsistency ratio.By combining these results with the acceleration analysis results,we determined that the strike of the second nodal plane with a larger dip angel is near the EW direction,which is consistent with the strike of acceleration transition zone.In addition,the microepicenter of the event does not coincide with the macroepicenter.These findings indicate that the nodal plane of strike 96°,dip 53°,and rake-102°may coincide with the seismogenic fault.Although the work in this study is a preliminary analysis for acceleration records and seismic digital waveform data,the results can provide a reference for quick determination of earthquake influence field and hazard assessment following a large earthquake and are highly significant for earthquake emergency response and disaster relief.
An earthquake with a magnitude(ML) of 2.1 occurred at 16:40 UTC,October 12,2011,in the Shijingshan district in Beijing with an epicenter at 39.95° N,116.16° E.Eleven near-field strong motion stations,located less than 20 km from the epicenter,clearly recorded temporal variation of acceleration during the earthquake.The largest value of peak ground acceleration in the east-west(EW) and north-south(NS) components,22.528 gal and 30.989 gal,respectively,were both recorded by station LSG,which is situated approximately 5.6 km from epicenter.The largest value of peak ground acceleration in the vertical component was 12.797 gal,recorded by station CCS at an epicenter distance of 2.2 km.We synthesized the horizontal component by EW and NS records and used Generic Mapping Tools(GMT) software to mesh and illustrate the influence of horizontal and vertical acceleration on the field contour map.The results show that generally,the value of the NS component is larger than that of the EW component,and the horizontal component is larger than the vertical.Moreover,the acceleration distribution and influence field contour map of the horizontal component shows that peak ground acceleration in the southern area is a low value and that in the northern area is high.In addition,the two regions are divided by a transition zone that strikes near east-west(EW) or NEE.We obtained the average peak ground value of three components at 1 s intervals from station records after the earthquake occurred,which we synthesized into horizontal and vertical components to illustrate temporal variations in the map produced by GMT.After analyzing the average value records and temporal variation map,we detected that the decay in the NS direction is faster than that in the EW direction and that decay is faster in the vertical component than that in the horizontal component.Excepting the near-field strong motion stations,23 Capital Circle broadband digital seismic stations recorded digital waveform data during the earthquake.We interpreted initial P-wave polarity from these records and employed grid-point test method to obtain the Focal Mechanism Solution of the event.Results indicate normal faulting dominant in the Beijing-Tianjin area.The best double couple solution of the event is 295°,39° and-74° for strike,dip and rake angel,respectively;those of the other nodal plane are 96°,53°,and-102° with a 13% inconsistency ratio.By combining these results with the acceleration analysis results,we determined that the strike of the second nodal plane with a larger dip angel is near the EW direction,which is consistent with the strike of acceleration transition zone.In addition,the microepicenter of the event does not coincide with the macroepicenter.These findings indicate that the nodal plane of strike 96°,dip 53°,and rake-102°may coincide with the seismogenic fault.Although the work in this study is a preliminary analysis for acceleration records and seismic digital waveform data,the results can provide a reference for quick determination of earthquake influence field and hazard assessment following a large earthquake and are highly significant for earthquake emergency response and disaster relief.
引文
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[5]闵祥仪,姚凯,何新社.2003年10月25日甘肃民乐—山丹MS6.1地震强震近场记录和分析[J].西北地震学报,2003,25(4):289-292.Min X Y,Yao K,He X S.Strong Motion Records and Pre-liminary Analysis for Minle-Shandan MS6.1Earthquake onOct.25,2003,Gansu Province[J].Northwestern Seismologi-cal Journal,2003,25(4):289-292.
[6]乔震元,刘本玉,张远富.汶川8.0级地震峰值地震动特性研究[J].西北地震学报,2011,33(1):92-95.Qiao Z Y,Liu B Y,Zhang Y F.Research on the Peak GroundMotion Characteristics of Wenchuan MS8.0Earthquake[J].Northwestern Seismological Journal,2011,33(1):92-95.
[7]姚凯,孙崇绍,朱珊珊,等.2008年汶川地震后的三次强余震地表峰值加速度衰减场研究[J].西北地震学报,2012,34(1):99-104.Yao K,Sun C S,Zhu S S,et al.Study on PGA Attenuation ofThree Strong Aftershocks of 2008 Wenchuan Earthquake[J].Northwestern Seismological Journal,2012,34(1):99-104.
[8]赖敏,余桦,孙玮,等.2007年3月5日攀枝花3.5级地震强震近场记录初步分析[J].四川地震,2008,3:24-30.Lai M,Yu H,Sun W,et al.Near-field Strong AccelerationRecords and Preliminary Analysis of Panzhihua ML3.5Earth-quake on 5March 2007,Sichuan Province[J].Earthquake Re-search in Sichuan,2008,3:24-30.
[9]卞真付,姚兰予,郭巍,等.河北文安5.1级地震首都圈实时强震动台网加速度记录分析[J].地震研究,2009,32(2):145-150.Bian Z F,Yao L Y,Guo W,et al.The Acceleration RecordsAnalysis of the M5.1 Wen'an Hebei Earthquake Recorded bythe Capital Real-time Digital Strong Motion Network[J].Journal of Seismological Research,2009,32(2):145-150.
[10]W Suzuki,S Aoi,H sekiguchi.Rupture Process of the 2008Iwate-Miyagi Nairiku,Japan,Earthquake Derived fromNear-source Strong-motion Recors[J].Bull.Seismol.Soc.Am.,2010.100(1):256-266.
[11]李恒,李井冈,王墩,等.竖直与水平向地震动加速度峰值比统计特征分析[J].地震研究,2010,33(2):195-199.Li H,Li J G,Wang D,et al.Analysis of Statistic Character-istics of Peak Ratios in Vertical and Horizontal Ground Mo-tion Acceleration[J].Journal of Seismological Research,2010,33(2):195-199.
[12]罗艳,崇加军,倪四道,等.首都圈地区莫霍面起伏及沉积层厚度[J].地球物理学报,2008,51(4):1135-1145.Luo Y,Chong J J,Ni S D,et al.Moho Depth and Sedime-tary Thickness in Capital Region[J].Chinese Journal of Geo-physics,2008,51(4):1135-1145.
[13]刘保金,胡平,等.北京平原西北部地壳浅部结构和隐伏活动断裂——由地震反射剖面揭示[J].地球物理学报,2009,52(8):2015-2025.Liu B J,Hu P,Chen Y,et al.The Crustal Shallow Struc-tures and Buried Active Faults Revealed by Seismic ReflectionProfiles in Northwestern Area of Beijing Plain[J].ChineseJournal of Geophysics,2009,52(8):2015-2025.
[14]任清芳,张成科,张先康,等.八达岭及周缘地区壳幔结构与潜在震源探讨[J].西北地震学报,1997,19(3):56-62.Ren Q F,Zhang C K,Zhang X K,et al.Discussion onStructure of Crust and Upper Mantle and Potential Focal Re-gion in Badaling and Its Neighborhood[J].NorthwesternSeismological Journal,1997,19(3):56-62.
[15]武敏捷,林向东,徐平.华北北部地区震源机制解及构造应力场特征分析[J].大地测量与地球动力学,2011,31(5):39-43.Wu M J,Lin X D,Xu P.Analysis of Focal Mechanism andTectonic Stress Field Features in Northern Part of North Chi-na[J].Journal of Geodesy and Geodynamics,2011,31(5):39-43.
[16]兰从欣,邢成起,苗春兰,等,近年首都圈地区中小地震震源机制解及其特征分析[J].华北地震科学,2005,23(4):21-25.Ren Q F,Zhang C K,Zhang X K,et al.Discussion onStructure of Crust and Upper Mantle and Potential Focal Re-gion in Badaling and Its Neighborhood[J].North ChinaEarthquake Sciences,1997,19(3):56-62.
[17]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[J].地球物理学报,2009,52(5):1402-1411.Yu C Q,Tao K,Cui X F.P-wave First-motion Focal Mecha-nism Solutions and Their Quality Evaluation[J].ChineseJournal of Geophysics,2009,52(5):1402-1411.
[18]胡幸平,俞春泉,陶开,等.利用P波初动资料求解汶川地震及其强余震震源机制解[J].地球物理学报,2008,51(6):1711-1718.Hu X P,Yu C Q,Tao K,et al.Focal Mechanism Solutionsof Wenchuan Earthquake and Its Strong Aftershocks Ob-tained from Initial P wave Polarity Analysis[J].ChineseJournal of Geophysics,2008,51(6):1711-1718.
[19]许忠淮,阎明,赵仲和.京津塘张地区小地震的平均释放应力场的方向特征[J].地震学报,1979,1(2):52-58.Xu Z H,Yan M,Zhao Z H.Evaluation of the Direction ofTectonic Stress in North China from Recorded Data of ALarge Number of Small earthquakes[J].Acta SeismologicaSinica,1983,5(3):268-279.
[2]陈琳,张明,董奕,等.索基于地震动峰值加速度的地震灾害评估方法[J].高原地震,2011,23(3):67-70.Chen L,Zhang M,Dong Y,et al.The Method of EarthquakeHazard Estimation Based on Peak Acceleration of Ground Mo-tion[J].Plateau Earthquake Research,2011,23(3):67-70.
[3]卢大伟,姚凯,闵祥仪,等.兰州观象台存放台阵汶川MS8.0强震动记录分析[J].西北地震学报,2011,33(2):171-176.Lu D W,Yao K,Min X Y,et al.Strong Motion Records ofPaking Array in Lanzhou Earth Observatary for WenchuanMS8.0Earthquake and Preliminary Analysis[J].Northwest-ern Seismological Journal,2011,33(2):171-176.
[4]刘旭宙,张元生,周民都,等.汶川MS8.0地震兰州烈度速报强震动记录与初步分析[J].西北地震学报,2010,32(4):376-380.Liu X Z,Zhang Y S,Zhou M D et al.Strong Ground MotionRecords of Wenchuan MS8.0Earthquake from the Seismic In-tensity Rapid Reporting Stations in Lanzhou and Its Prelimina-ry Analysis[J].Northwestern Seismological Journal,2010,32(4):376-380.
[5]闵祥仪,姚凯,何新社.2003年10月25日甘肃民乐—山丹MS6.1地震强震近场记录和分析[J].西北地震学报,2003,25(4):289-292.Min X Y,Yao K,He X S.Strong Motion Records and Pre-liminary Analysis for Minle-Shandan MS6.1Earthquake onOct.25,2003,Gansu Province[J].Northwestern Seismologi-cal Journal,2003,25(4):289-292.
[6]乔震元,刘本玉,张远富.汶川8.0级地震峰值地震动特性研究[J].西北地震学报,2011,33(1):92-95.Qiao Z Y,Liu B Y,Zhang Y F.Research on the Peak GroundMotion Characteristics of Wenchuan MS8.0Earthquake[J].Northwestern Seismological Journal,2011,33(1):92-95.
[7]姚凯,孙崇绍,朱珊珊,等.2008年汶川地震后的三次强余震地表峰值加速度衰减场研究[J].西北地震学报,2012,34(1):99-104.Yao K,Sun C S,Zhu S S,et al.Study on PGA Attenuation ofThree Strong Aftershocks of 2008 Wenchuan Earthquake[J].Northwestern Seismological Journal,2012,34(1):99-104.
[8]赖敏,余桦,孙玮,等.2007年3月5日攀枝花3.5级地震强震近场记录初步分析[J].四川地震,2008,3:24-30.Lai M,Yu H,Sun W,et al.Near-field Strong AccelerationRecords and Preliminary Analysis of Panzhihua ML3.5Earth-quake on 5March 2007,Sichuan Province[J].Earthquake Re-search in Sichuan,2008,3:24-30.
[9]卞真付,姚兰予,郭巍,等.河北文安5.1级地震首都圈实时强震动台网加速度记录分析[J].地震研究,2009,32(2):145-150.Bian Z F,Yao L Y,Guo W,et al.The Acceleration RecordsAnalysis of the M5.1 Wen'an Hebei Earthquake Recorded bythe Capital Real-time Digital Strong Motion Network[J].Journal of Seismological Research,2009,32(2):145-150.
[10]W Suzuki,S Aoi,H sekiguchi.Rupture Process of the 2008Iwate-Miyagi Nairiku,Japan,Earthquake Derived fromNear-source Strong-motion Recors[J].Bull.Seismol.Soc.Am.,2010.100(1):256-266.
[11]李恒,李井冈,王墩,等.竖直与水平向地震动加速度峰值比统计特征分析[J].地震研究,2010,33(2):195-199.Li H,Li J G,Wang D,et al.Analysis of Statistic Character-istics of Peak Ratios in Vertical and Horizontal Ground Mo-tion Acceleration[J].Journal of Seismological Research,2010,33(2):195-199.
[12]罗艳,崇加军,倪四道,等.首都圈地区莫霍面起伏及沉积层厚度[J].地球物理学报,2008,51(4):1135-1145.Luo Y,Chong J J,Ni S D,et al.Moho Depth and Sedime-tary Thickness in Capital Region[J].Chinese Journal of Geo-physics,2008,51(4):1135-1145.
[13]刘保金,胡平,等.北京平原西北部地壳浅部结构和隐伏活动断裂——由地震反射剖面揭示[J].地球物理学报,2009,52(8):2015-2025.Liu B J,Hu P,Chen Y,et al.The Crustal Shallow Struc-tures and Buried Active Faults Revealed by Seismic ReflectionProfiles in Northwestern Area of Beijing Plain[J].ChineseJournal of Geophysics,2009,52(8):2015-2025.
[14]任清芳,张成科,张先康,等.八达岭及周缘地区壳幔结构与潜在震源探讨[J].西北地震学报,1997,19(3):56-62.Ren Q F,Zhang C K,Zhang X K,et al.Discussion onStructure of Crust and Upper Mantle and Potential Focal Re-gion in Badaling and Its Neighborhood[J].NorthwesternSeismological Journal,1997,19(3):56-62.
[15]武敏捷,林向东,徐平.华北北部地区震源机制解及构造应力场特征分析[J].大地测量与地球动力学,2011,31(5):39-43.Wu M J,Lin X D,Xu P.Analysis of Focal Mechanism andTectonic Stress Field Features in Northern Part of North Chi-na[J].Journal of Geodesy and Geodynamics,2011,31(5):39-43.
[16]兰从欣,邢成起,苗春兰,等,近年首都圈地区中小地震震源机制解及其特征分析[J].华北地震科学,2005,23(4):21-25.Ren Q F,Zhang C K,Zhang X K,et al.Discussion onStructure of Crust and Upper Mantle and Potential Focal Re-gion in Badaling and Its Neighborhood[J].North ChinaEarthquake Sciences,1997,19(3):56-62.
[17]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[J].地球物理学报,2009,52(5):1402-1411.Yu C Q,Tao K,Cui X F.P-wave First-motion Focal Mecha-nism Solutions and Their Quality Evaluation[J].ChineseJournal of Geophysics,2009,52(5):1402-1411.
[18]胡幸平,俞春泉,陶开,等.利用P波初动资料求解汶川地震及其强余震震源机制解[J].地球物理学报,2008,51(6):1711-1718.Hu X P,Yu C Q,Tao K,et al.Focal Mechanism Solutionsof Wenchuan Earthquake and Its Strong Aftershocks Ob-tained from Initial P wave Polarity Analysis[J].ChineseJournal of Geophysics,2008,51(6):1711-1718.
[19]许忠淮,阎明,赵仲和.京津塘张地区小地震的平均释放应力场的方向特征[J].地震学报,1979,1(2):52-58.Xu Z H,Yan M,Zhao Z H.Evaluation of the Direction ofTectonic Stress in North China from Recorded Data of ALarge Number of Small earthquakes[J].Acta SeismologicaSinica,1983,5(3):268-279.
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