应用动态复合震源模型模拟汶川M_w 7.9地震强地面运动
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摘要
2008年5月12日中国汶川地区发生M_w7.9地震,震中位置103.4°E,31.0°N.主要发震断层空间展布长达300多公里,由南西方向到北东方向呈现明显的分段性,汶川—映秀段逆冲为主兼有少量的右旋走滑分量;安县—北川段为逆冲-右旋走滑的断层错动;青川段以右旋走滑为主兼有少量逆冲分量.采用改进后的复合震源强地面运动预测模型,建立了长为320km,宽为20km的断层破裂运动学模型,实现了断层分段、空间倾角、滑动方向连续变化的动态设定.数值模拟结果给出了近断层两侧(上、下盘)的地面加速度的分布特征,并同卧龙、郫县走石由及绵竹清平强震观测记录进行了对比分析.模拟加速度时程曲线无论在波形、持续时间、频率分量、峰值大小同观测记录都具有较好的相似性.利用现有83个已知经纬度台站的强震实测数据及数值模拟的结果同Boore等的新一代衰减关系(NGA)进行比较,对比模拟与实际观测水平峰值加速度的一致程度.近断层峰值加速度分布特征则进一步显示了在汶川、北川和青川附近明显的高值分布区域,同野外地质调查相一致.进一步的分析结果也表明,汶川—映秀段逆冲为主的断层上盘的运动量远大于断层下盘,在距离断层地表出露位置5km处,峰值加速度N-S、E-W及UP方向分量的比值分别为1.72:1、2.5:1及1.77:1.本文中给出的动态复合震源模型和近断层区域强震模拟的计算方法,对大震强地面运动的预测及实现近实时强地面运动分布特征的圈定(Shaking Map)有着重要的实际意义.
The great Wenchuan Earthquake of May 12,2008,M_w7.9 occurred in Sichuan province of western China with the epicenter at longitude 103.4°E and latitude 31.0°N.The main fault ruptured more than 300km in length with a striking direction from southwest toward northeast along the Longmenshan Central Fault.The geological and geophysical investigations also revealed significant fault segmentation during the earthquake faulting.The Wenchuan-Yingxiu segment of the fault is dominated by pure thrusting with a dip angle about 40°,while the Beichuan-Anxian segment of the fault in the central part of the main fault underwent both thrusting and strike-slipping with a dip angle of 70°,and the remained segment of the fault,a part of the Qingchuan fault,underwent an almost pure strike slip motion with a dip angle of 80°.In this study,a modified composite source model,named as dynamical composite source model(DCSM),has been developed to simulate near-fault strong ground motion with associated fault rupture properties from a kinematic point of view.For the Wenchuan event,a specific finite fault model with a length of 320 km and a width of 20 km is constructed for simulation purpose.Moreover, the fault model consists of three major segments in which each segment could has a specific geometry related to the dip angle and strike direction.In addition,the rakes related to the slip direction on the fault plane of each segment could be assigned dynamically based on the focal mechanism solution.For comparing purpose,we conduct broadband ground motion predictions for three typical near-fault strong motion stations of Wolong,Pixian-Zoushishan and Mianzhu-Qingping. In general,the synthetic seismograms produced for these stations have good agreement with the observations in time histories,waveforms,peak values and frequency contents,which indicate that the numerical technique of current source model could reproduce the main characteristics of strong ground motion for the Wenchuan Earthquake.In addition,the near-fault peak ground acceleration(PGA) distributions resulted from current simulation show much higher PGA values in the areas of Wenchuan,Beichuan and Qingchuan than other places,which is consistent with recent field observation and reports.The map of PGA distribution also indicates that,compared with other two segments of earthquake faulting,the ground motion caused by Wenchuan-Yingxiu thrusting is much stronger on the hanging wall than on the footwall,for example,the PGA ratios of the hanging wall to footwall could reach 1.72:1,2.5:1 and 1.77:1 for N-S,E-W and UP components,respectively,at a given distance of 5 km from the fault trace on both sides of the fault.In fact,the numerical modeling developed in this study has the great potential application in the ground motion estimation/prediction for the earthquake engineering purpose.Furthermore,the numerical algorithm could also be used to generate the near-real-time shaking map in the implementation level if incorporated current finite fault inverse technique.
The great Wenchuan Earthquake of May 12,2008,M_w7.9 occurred in Sichuan province of western China with the epicenter at longitude 103.4°E and latitude 31.0°N.The main fault ruptured more than 300km in length with a striking direction from southwest toward northeast along the Longmenshan Central Fault.The geological and geophysical investigations also revealed significant fault segmentation during the earthquake faulting.The Wenchuan-Yingxiu segment of the fault is dominated by pure thrusting with a dip angle about 40°,while the Beichuan-Anxian segment of the fault in the central part of the main fault underwent both thrusting and strike-slipping with a dip angle of 70°,and the remained segment of the fault,a part of the Qingchuan fault,underwent an almost pure strike slip motion with a dip angle of 80°.In this study,a modified composite source model,named as dynamical composite source model(DCSM),has been developed to simulate near-fault strong ground motion with associated fault rupture properties from a kinematic point of view.For the Wenchuan event,a specific finite fault model with a length of 320 km and a width of 20 km is constructed for simulation purpose.Moreover, the fault model consists of three major segments in which each segment could has a specific geometry related to the dip angle and strike direction.In addition,the rakes related to the slip direction on the fault plane of each segment could be assigned dynamically based on the focal mechanism solution.For comparing purpose,we conduct broadband ground motion predictions for three typical near-fault strong motion stations of Wolong,Pixian-Zoushishan and Mianzhu-Qingping. In general,the synthetic seismograms produced for these stations have good agreement with the observations in time histories,waveforms,peak values and frequency contents,which indicate that the numerical technique of current source model could reproduce the main characteristics of strong ground motion for the Wenchuan Earthquake.In addition,the near-fault peak ground acceleration(PGA) distributions resulted from current simulation show much higher PGA values in the areas of Wenchuan,Beichuan and Qingchuan than other places,which is consistent with recent field observation and reports.The map of PGA distribution also indicates that,compared with other two segments of earthquake faulting,the ground motion caused by Wenchuan-Yingxiu thrusting is much stronger on the hanging wall than on the footwall,for example,the PGA ratios of the hanging wall to footwall could reach 1.72:1,2.5:1 and 1.77:1 for N-S,E-W and UP components,respectively,at a given distance of 5 km from the fault trace on both sides of the fault.In fact,the numerical modeling developed in this study has the great potential application in the ground motion estimation/prediction for the earthquake engineering purpose.Furthermore,the numerical algorithm could also be used to generate the near-real-time shaking map in the implementation level if incorporated current finite fault inverse technique.
引文
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[5]Zeng Y,Anderson J G,Yu G.A composite source model for computing realistic synthetic strong ground motions.Geophys Res Lett,1994,21(8):725-728
[6]Herrero A,Bernard P.A kinematic self similar rupture process for earthquakes.Bull Seism Soc Amer,1994,84 (4):1226-1228
[7]刘博研,史保平,张健.复合地震源模拟强地面运动:以1679年三河—平谷M_s8.0地震为例.地震学报,2007,29 (3):302-313 Liu B Y,Shi B P,Zhang J.Strong motion simulation by the composite source modeling:A case study of 1679 M_s8.0 Sanhe-Pinggu earthquake.ACTA Seismologica Sinica(in Chinese),2007,20(3):319-331
[8]史保平,刘博研,张健.特征地震强地面运动参数衰减公式模拟.地震学报,2007,29(4):391-399 Shi B P,Liu B Y,Zhang J.Development of attenuation relation for the near fault ground motion from the characteristic earthquake.ACTA Seismologica Sinica(in Chinese),2007,20(4):416-424
[9]王卫民,赵连锋,李娟等.四川汶川8.0级地震震源过程.地球物理学报,2008,51(5):1403-1410 Wang W M,Zhao L F,Li J,et al.Rupture process of the M_s8.0 Wenchuan earthquake of Sichuan,China.Chinese J. Geophys.(in Chinese),2008,51(5):1403-1410
[10]Boore D M,G M Atkinson.Boore- Atkinson NGA ground motion relations for the geometric mean horizontal component of peak and spectral ground motion parameters.PEER Report 2007/01.2007:Pacific earthquake engineering research center
[11]李小军,周正华,于海英等.汶川8.0地震强震动观测及记录初步分析.见:汶川地震建筑震害调查与灾后重建分析报告.北京:中国建筑工业出版社,2008 Li X J,Zhou Z H,Yu H Y,et al.Strong ground motion observations analysis of Wenchuan,M_s8.0 earthquake.In: Analysis Report of the Wenchuan Earthquake Damage Survey and Architectural Post- Disaster Reconstruction.Beijing: China Architecture and Building Press(in Chinese),2008
[12]Boatwright J.The dynamic models for far-field acceleration. Bull Seism Soc Amer,1982,72(4):1049-1068
[13]Boatwright J.The seismic radiation from composite models of faulting.Bull Seism Soc Amer,1988,78(2):489-508
[14]Frankel A.High frequency spectral falloff for earthquakes, fractal dimension of strength on faults.J Geophys Res, 1991,96(134):6291-6302
[15]Zeng Y,Anderson J G,Yu G.A method for direct computing of the differential seismogram with respect to the velocity change in a layered elastic solid.Bull Seism Soc Amer,1995,85(1):300-307
[16]Zeng Y,Anderson J G.A composite source modeling of the 1994 Northridge earthquake using genetic algorithm.Bull Seism Soc Amer,1996,86(1B):71-83
[17]Brune J N.Tectonic stress and spectra of seismic shear waves from earthquakes.J Geophys Res,1970,75(26):4997-5009
[18]Brune J N.Correction to tectonic stress and spectra of seismic shear waves from earthquakes.J.Geophys.Res.,1971,76 (20):5002
[19]Aki K,Richards F G.Quantitative Seismology:Theory and Method.New York:W H Freeman and Company,1980.557
[20]Chen Ji,Gavin Hayes.Finite fault model.Preliminary result of the May 12,2008 M_w7.9 Eastern Sichuan,2008.China Earthquake.http://earthquake.usgs.gov/eqcenter/eqinthenews/ 2008/us2008ryan/finite_fault.php[2010-04-06]
[21]刘启元,李昱,陈九辉等.汶川M_s8.0地震:地壳上地幔S波速度结构的初步研究.地球物理学报,2009,52(2):309-319 Liu Q Y,Li Y,Chen J H,et al.The M_s8.0 Wenchuan earthquake:Preliminary results from the western Sichuan mobile seismic array observations.Seismology and Geology (in Chinese),2009,52(2):309-319
[22]兰景岩,吕悦军,彭艳菊等.汶川8.0强震记录的近断层效应的初步分析.见:汶川8.0级地震地壳动力学研究专辑.北京:地震出版社,2009 Lan J Y,L(u|¨) Y J,Peng Y J,et al.A preliminary analysis on the near-fault effect of strong-motion observations from the M_s8.0 Wenchuan earthquake,China.In:Xie F R,ed. Crustal Dynamics of the Wenchuan M_s8.0 Earthquake(in Chinese).Beijing:Seismological Press,2009
[23]刘静,张智慧,文力等.汶川8级大地震同震破裂的特殊性及构造意义.地质学报,2008,82(12):1707-1722 Liu J,Zhang Z H,Wen L,et al.The M_s8.0 Wenchuan earthquake co- seismic rupture and its tectonic implications. Acta Geolo gica Sinica(in Chinese),2008,82(12):1707 - 1722
[24]中国地震局震害防御司编.汶川8.0级地震未校正加速度记录.中国强震记录汇报,第十二集,第一卷.北京:地震出版社,2008 The Department of Earthquake Disaster Prevention,China Earthquake Administration.Report on Strong Earthquake Motion Records in China(in Chinese).Beijing:Earthquake Press,2008,12(1)
[25]Boore D M,Joyner W B,Fumal T E.Equations for estimating horizontal response spectra and peak acceleration from Western North American Earthquakes:A summary of recent work.SeismResLett,1997,68(1):128-153
[26]Li Xiaojun,Zhou Zhenghua,Yu Haiying,et al.Strong motion observations and recordings from the great Wenchuan Earthquake.Earthquake Engineering and Engineering Vibration, 2008,7(3):235-246
[27]于海英,王栋,杨永强等.汶川8.0级地震强震动加速度记录的初步分析.地震工程与工程振动,2009,29(1):1-13 Yu H Y,Wang D,Yang Y Q,et al.The preliminary analysis of strong ground motion records from the Ms8.0 Wenchuan earthquake.Journal of Earthquake Engineering and Engineering Vibration(in Chinese),2009,29(1):1-13
[28]Somerville P G.Magnitude scaling of the near fault rupture directivitypulse.Phys.Earth.Planetary.Int,2003,137(1- 4):201 -212
[29]Oglesby D D,Archuleta R J,Nielsen S B.Earthquakes on dipping faults:The effects if broken symmetry.Science, 1998,280(5366):1055-1059
[30]Shi B,Anooshehpoor A,Brune J N,et al.Dynamic of thrust faulting:2D lattice model.Bull Seism Soc Amer,1998,88 (6):1484-1494
[2]徐锡伟,闻学泽,叶建青等.汶川M_s8.0地震地表破裂带及其发震构造.地震地质,2008,30(3):597-629 Xu X W,Wen X Z,Ye J Q,et al.The M_s8.0 Wenchuan earthquake surface rupture and its seismogenic structure. Seismology and Geology(in Chinese),2008,30(3):597 - 629
[3]李志强,袁一凡,李晓丽等.对汶川地震宏观震中和极震区的认识.地震地质,2008,30(3):768-777 LiZ Z,Yuan Y F,Li X L,et al.Some insights into the macro- epicenter and meizoseismal region of Wenchuan earthquake.Seismology and Geology(in Chinese),2008,30 (3):768-777
[4]Hartzell S,Harmsen S,Frankel A,et al.Calculation of broadband time histories of ground motion:comparison of methods and validation using strong -ground motion from the 1994 northridge earthquake.Bull Seism Soc Amer,1999,89 (6):1484--1504
[5]Zeng Y,Anderson J G,Yu G.A composite source model for computing realistic synthetic strong ground motions.Geophys Res Lett,1994,21(8):725-728
[6]Herrero A,Bernard P.A kinematic self similar rupture process for earthquakes.Bull Seism Soc Amer,1994,84 (4):1226-1228
[7]刘博研,史保平,张健.复合地震源模拟强地面运动:以1679年三河—平谷M_s8.0地震为例.地震学报,2007,29 (3):302-313 Liu B Y,Shi B P,Zhang J.Strong motion simulation by the composite source modeling:A case study of 1679 M_s8.0 Sanhe-Pinggu earthquake.ACTA Seismologica Sinica(in Chinese),2007,20(3):319-331
[8]史保平,刘博研,张健.特征地震强地面运动参数衰减公式模拟.地震学报,2007,29(4):391-399 Shi B P,Liu B Y,Zhang J.Development of attenuation relation for the near fault ground motion from the characteristic earthquake.ACTA Seismologica Sinica(in Chinese),2007,20(4):416-424
[9]王卫民,赵连锋,李娟等.四川汶川8.0级地震震源过程.地球物理学报,2008,51(5):1403-1410 Wang W M,Zhao L F,Li J,et al.Rupture process of the M_s8.0 Wenchuan earthquake of Sichuan,China.Chinese J. Geophys.(in Chinese),2008,51(5):1403-1410
[10]Boore D M,G M Atkinson.Boore- Atkinson NGA ground motion relations for the geometric mean horizontal component of peak and spectral ground motion parameters.PEER Report 2007/01.2007:Pacific earthquake engineering research center
[11]李小军,周正华,于海英等.汶川8.0地震强震动观测及记录初步分析.见:汶川地震建筑震害调查与灾后重建分析报告.北京:中国建筑工业出版社,2008 Li X J,Zhou Z H,Yu H Y,et al.Strong ground motion observations analysis of Wenchuan,M_s8.0 earthquake.In: Analysis Report of the Wenchuan Earthquake Damage Survey and Architectural Post- Disaster Reconstruction.Beijing: China Architecture and Building Press(in Chinese),2008
[12]Boatwright J.The dynamic models for far-field acceleration. Bull Seism Soc Amer,1982,72(4):1049-1068
[13]Boatwright J.The seismic radiation from composite models of faulting.Bull Seism Soc Amer,1988,78(2):489-508
[14]Frankel A.High frequency spectral falloff for earthquakes, fractal dimension of strength on faults.J Geophys Res, 1991,96(134):6291-6302
[15]Zeng Y,Anderson J G,Yu G.A method for direct computing of the differential seismogram with respect to the velocity change in a layered elastic solid.Bull Seism Soc Amer,1995,85(1):300-307
[16]Zeng Y,Anderson J G.A composite source modeling of the 1994 Northridge earthquake using genetic algorithm.Bull Seism Soc Amer,1996,86(1B):71-83
[17]Brune J N.Tectonic stress and spectra of seismic shear waves from earthquakes.J Geophys Res,1970,75(26):4997-5009
[18]Brune J N.Correction to tectonic stress and spectra of seismic shear waves from earthquakes.J.Geophys.Res.,1971,76 (20):5002
[19]Aki K,Richards F G.Quantitative Seismology:Theory and Method.New York:W H Freeman and Company,1980.557
[20]Chen Ji,Gavin Hayes.Finite fault model.Preliminary result of the May 12,2008 M_w7.9 Eastern Sichuan,2008.China Earthquake.http://earthquake.usgs.gov/eqcenter/eqinthenews/ 2008/us2008ryan/finite_fault.php[2010-04-06]
[21]刘启元,李昱,陈九辉等.汶川M_s8.0地震:地壳上地幔S波速度结构的初步研究.地球物理学报,2009,52(2):309-319 Liu Q Y,Li Y,Chen J H,et al.The M_s8.0 Wenchuan earthquake:Preliminary results from the western Sichuan mobile seismic array observations.Seismology and Geology (in Chinese),2009,52(2):309-319
[22]兰景岩,吕悦军,彭艳菊等.汶川8.0强震记录的近断层效应的初步分析.见:汶川8.0级地震地壳动力学研究专辑.北京:地震出版社,2009 Lan J Y,L(u|¨) Y J,Peng Y J,et al.A preliminary analysis on the near-fault effect of strong-motion observations from the M_s8.0 Wenchuan earthquake,China.In:Xie F R,ed. Crustal Dynamics of the Wenchuan M_s8.0 Earthquake(in Chinese).Beijing:Seismological Press,2009
[23]刘静,张智慧,文力等.汶川8级大地震同震破裂的特殊性及构造意义.地质学报,2008,82(12):1707-1722 Liu J,Zhang Z H,Wen L,et al.The M_s8.0 Wenchuan earthquake co- seismic rupture and its tectonic implications. Acta Geolo gica Sinica(in Chinese),2008,82(12):1707 - 1722
[24]中国地震局震害防御司编.汶川8.0级地震未校正加速度记录.中国强震记录汇报,第十二集,第一卷.北京:地震出版社,2008 The Department of Earthquake Disaster Prevention,China Earthquake Administration.Report on Strong Earthquake Motion Records in China(in Chinese).Beijing:Earthquake Press,2008,12(1)
[25]Boore D M,Joyner W B,Fumal T E.Equations for estimating horizontal response spectra and peak acceleration from Western North American Earthquakes:A summary of recent work.SeismResLett,1997,68(1):128-153
[26]Li Xiaojun,Zhou Zhenghua,Yu Haiying,et al.Strong motion observations and recordings from the great Wenchuan Earthquake.Earthquake Engineering and Engineering Vibration, 2008,7(3):235-246
[27]于海英,王栋,杨永强等.汶川8.0级地震强震动加速度记录的初步分析.地震工程与工程振动,2009,29(1):1-13 Yu H Y,Wang D,Yang Y Q,et al.The preliminary analysis of strong ground motion records from the Ms8.0 Wenchuan earthquake.Journal of Earthquake Engineering and Engineering Vibration(in Chinese),2009,29(1):1-13
[28]Somerville P G.Magnitude scaling of the near fault rupture directivitypulse.Phys.Earth.Planetary.Int,2003,137(1- 4):201 -212
[29]Oglesby D D,Archuleta R J,Nielsen S B.Earthquakes on dipping faults:The effects if broken symmetry.Science, 1998,280(5366):1055-1059
[30]Shi B,Anooshehpoor A,Brune J N,et al.Dynamic of thrust faulting:2D lattice model.Bull Seism Soc Amer,1998,88 (6):1484-1494
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