汶川8.0级地震前区域应力场动态研究
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摘要
利用成都、昆明遥测数字地震波形记录资料,研究大量小震震源机制解和视应力值,分析了区域应力场动态和视应力值的时-空分布。给出川青地块平均应力场方位的时间变化。川青地块平均主应力场的方位在汶川8.0级地震前出现明显扰动,同时,地块力轴张量的倾角变化也很明显。得出2006～2007年川青块体逆冲型地震比例偏高,汶川8.0级地震前区域中小地震震源错动类型发生变化的结果,与区域地形变的分析结果是一致的。根据地震波形全波段计算辐射能量,求得的视应力σapp值揭示区域视应力值的微动态起伏过程与区域主压应力场方位的转折类似,可用于地块蕴震物理过程的探索。从汶川8.0级地震前的中短期视应力σapp值的空间分布看,震中所在的龙门山断裂带是低应力分布区,而相对高视应力则分布在外围地区。这些图像可能揭示了汶川8.0级地震前中短期发震构造附近呈现的闭锁现象。
This article uses the telemetry digital seismic waveform data from Chengdu and Kunming to study the focal mechanism solutions and the apparent stress values of a large number of small earthquakes, and analyzes the regional stress field dynamics and the spatio-temporal distribution of apparent stress values. The temporal variation of the average stress field azimuth in Sichuan-Qinghai block is given. The average principal stress field azimuth of Sichuan-Qinghai block had obvious disturbances before the Wenchuan MS8.0 earthquake. This may be related to status change of block stress field between the Sumatra MS9.0 earthquake on December 26, 2004 in Indonesia and the Wenchuan MS8.0 earthquake in 2008. The ratio of thrust-type earthquake in the Sichuan-Qinghai block was high from 2006 to 2007. The variations of the earthquake dislocation type of regional moderate and small earthquakes before the Wenchuan MS8.0 earthquake are consistent with the state change of block displacement field revealed by GPS data, and also identical with analysis results of crustal shortening velocity change which is vertical to Longmenshan fault zone. The apparent stress value is determined on the basis of the whole band of the seismic waveform to calculate radiation energy. The fluctuation shape of the fitting trend of the apparent stress line is related to strong and weak of regional seismicity. It reveals that the micro-dynamic fluctuation process of regional stress value is similar to the azimuth transition of regional principal compressive stress field, which can be used to grope for pregnant physical process. The higher value areas of apparent stress are the possible areas of potential seismic risk. It can be seen from the spatial distribution of the medium-and short-term apparent stress before the Wenchuan MS8.0 earthquake that the Longmenshan fault zone is low stress distribution area, and the relatively high apparent stress is in peripheral area. These images may show the lock phenomenon near the medium and short Wenchuan MS8.0 earthquake, for example, the focal parameter consistency of the sub-blocks in Sichuan and Yunnan Provinces changed with time, the thrust-type earthquakes in Sichuan-Qinghai block continually increased, the spatial distribution areas of the high apparent stress were discovered, and so on. The authors' continuous work in this aspect after the Wenchuan MS8.0 earthquake may further reveal the relationship between these phenomena and future great earthquake.
This article uses the telemetry digital seismic waveform data from Chengdu and Kunming to study the focal mechanism solutions and the apparent stress values of a large number of small earthquakes, and analyzes the regional stress field dynamics and the spatio-temporal distribution of apparent stress values. The temporal variation of the average stress field azimuth in Sichuan-Qinghai block is given. The average principal stress field azimuth of Sichuan-Qinghai block had obvious disturbances before the Wenchuan MS8.0 earthquake. This may be related to status change of block stress field between the Sumatra MS9.0 earthquake on December 26, 2004 in Indonesia and the Wenchuan MS8.0 earthquake in 2008. The ratio of thrust-type earthquake in the Sichuan-Qinghai block was high from 2006 to 2007. The variations of the earthquake dislocation type of regional moderate and small earthquakes before the Wenchuan MS8.0 earthquake are consistent with the state change of block displacement field revealed by GPS data, and also identical with analysis results of crustal shortening velocity change which is vertical to Longmenshan fault zone. The apparent stress value is determined on the basis of the whole band of the seismic waveform to calculate radiation energy. The fluctuation shape of the fitting trend of the apparent stress line is related to strong and weak of regional seismicity. It reveals that the micro-dynamic fluctuation process of regional stress value is similar to the azimuth transition of regional principal compressive stress field, which can be used to grope for pregnant physical process. The higher value areas of apparent stress are the possible areas of potential seismic risk. It can be seen from the spatial distribution of the medium-and short-term apparent stress before the Wenchuan MS8.0 earthquake that the Longmenshan fault zone is low stress distribution area, and the relatively high apparent stress is in peripheral area. These images may show the lock phenomenon near the medium and short Wenchuan MS8.0 earthquake, for example, the focal parameter consistency of the sub-blocks in Sichuan and Yunnan Provinces changed with time, the thrust-type earthquakes in Sichuan-Qinghai block continually increased, the spatial distribution areas of the high apparent stress were discovered, and so on. The authors' continuous work in this aspect after the Wenchuan MS8.0 earthquake may further reveal the relationship between these phenomena and future great earthquake.
引文
程万正、李桂芳、席敦礼,1990,马边地区地震动态应力场,四川地震,(3),26～31。
程万正、李桂芳、乔惠珍等,2002,四川沐川5.7级震群子序列的震源参数变化,中国地震,18(2),203～213.
程万正、刁桂苓、吕弋培等,2003a,川滇地块的震源力学机制、运动速率和活动方式,地震地质,25(1),71～86。
程万正、陈天长、魏娅玲等,2003b,2001年四川雅江6级地震的前震与余震震源参数的变化,地震学报,25(4),351～360。
程万正、陈天长、乔惠珍,2003,荣昌5.2级地震序列的震源参数及震区应力状态,地震,23(3),79～88。
程万正、张永久、阮祥,2006a,川滇次级地块震源机制解类型与一致性参数,地震学报,28(6),561～573。
程万正、陈学忠、乔慧珍等,2006b,四川地震辐射能量和视应力的研究,地球物理学进展,21(3),692～699。
程万正、阮祥、张致伟,2009,汶川8.0级地震序列及震型判定,29(1),15～25。
成尔林、李桂芳、陈和川等,1982.1976年四川省松潘—平武7.2级地震前后主压应力轴的方向特征,地震学报,4(2),15～19。
阚荣举、刘祖荫、王绍晋等,1983,龙陵地区大震前后平均应力轴取向的时间变化,地球物理学报,26(6),38～41。
胡新亮、刁桂苓、马瑾等,2004,利用数字地震记录的,振幅比资料测定小震震源机制解的可靠性分析,地震地质,26(2),347～353。
华祥文,1980,唐山强震前后北京、天津周围地区应力场的变化过程,地震学报,2(2),33～37。
江在森、方颖、武艳强等,2009,汶川8.0级地震前区域地壳运动与变形动态过程,地球物理学报,52(2),505～518。
梁尚鸿、李幼铭、束沛镒等,1984、利用区域地震台网、振幅比资料测定小震震源参数,地球物理学报,27(3),247～257。
马瑾、刘力强、马胜利等,1995,复杂构造应力扰动场与发震构造识别问的研究,地震地质,7(4),372～382。
阮祥、程万正,2008,云南鲁甸3次MS≥5.0地震破裂参数的研究.地震学报,30(1),97～102。
万永革,2008,美国Landers地震和Hector Mine地震前震源机制与主震机制一致现象的研究,中国地震,24(3),216～225。
王绍晋、付虹、卫爱民等,2001,川滇地区7级大震前中强震震源机制变化,地震研究,24(2),88～108。
王凯英、马瑾、顾国华等,2003,1996年川滇地区发生的一次应力转向事件,地学前缘,10(特刊),233～239。
许忠淮、刘玉芳、张郢珍,1979,京津唐张地区地震应力场的方向特征,地震学报,1(2),13～18。
钟继茂、程万正,2006,由多个地震震源机制解求川滇地区平均应力场,地震学报,28(4),337～346。
赵根模、楮宝珑、郭瑞芝,1984,宁河6.9级强震前小震主=应力轴取向的变化,地震学报,6(4),414～424。
张永久、彭立国、程万正,2006,马尔康地震序列震源参数研究,中国地震,22(1),85～93。
张永久、程万正,2007,用P、S波速度振幅比求小震机制解的可行性研究,中国地震,23(4),366～374。
张致伟、程万正、阮祥等,2009,汶川8.0级地震前龙门山断裂带的地震活动性和构造应力场特征,地震学报,31(2),117～127。
Aki,K.1966.Generation and propagation of G waves from the Niigata earthquake of June16,1964,estimation of earthquakemoment,released energy,and stress-strain drop from G wave spectrum,Bulletin of the Earthquake Research Institute,44,23～88.
Chen,X.Z.,Wang,X.P.,Wang,L.Y.,et al,2003.possibility of earlier judgement on seismic tendency after strong earthquakesupon their apparent stresses,Recent Developments in World Seismology.Serial,295(7),1～5.
Kanamori H.and Heaton T.H.,2001,Microscopic and macroscopic physics of earthquakes,GeoComplexity and the Physics ofEarthquakes,147～163.
Kanamori H.,2001.Energy budget of earthquakes and seismic efficiency.Earthquake Thermodynamics and Phase Transformationsin the Earth's Interior,76,293～305.
Rydelek,P,A,.and Sacks,I,S.1999,Large earthquake occurrence affected by small stress changes,Bull Seism Soc Am.89(3),822～828.
Snoke J.A.,Munsey J.W.,Teague A.C.,et al.1984,A program for focal mechanism determination by combined use of polarityand SV-P amplitude ratio data,Earthquake Notes,55(3),121～128.
Sadovsky,M A.1972,The processes preceding strong earthquakes in some regions of Middle Asian,Tectonophysics,14(3/4),116～l25.
Sadovsky M A.Nersesov I L,1974,Ferecasts of earthquakes on the basis of complex geophysical features,Tectonophysics,23(3),135～142.
Seeber L,Armbruster J G.,2000,Earthquakes as beacons of stress change,Nature,407,69～72.
Wyss,M.and Brune,J.N.,1968,Seismic moment,stress,and source dimensions for earthquakes in the California-Nevadaregion,J.Geophys.Res.,73,4681～4694.
Wyss,M.,1970a,Apparent stresses of earthquakes on ridges compared to apparent stresses of earthquakes in trenches.Geophys,J.R.astr.Soc.,19,479～484.
Wyss,M,1970b,Stress estimates for South American shallow and deep earthquakes,J.Geophys.Res.,75(8),1529～1544.
程万正、李桂芳、乔惠珍等,2002,四川沐川5.7级震群子序列的震源参数变化,中国地震,18(2),203～213.
程万正、刁桂苓、吕弋培等,2003a,川滇地块的震源力学机制、运动速率和活动方式,地震地质,25(1),71～86。
程万正、陈天长、魏娅玲等,2003b,2001年四川雅江6级地震的前震与余震震源参数的变化,地震学报,25(4),351～360。
程万正、陈天长、乔惠珍,2003,荣昌5.2级地震序列的震源参数及震区应力状态,地震,23(3),79～88。
程万正、张永久、阮祥,2006a,川滇次级地块震源机制解类型与一致性参数,地震学报,28(6),561～573。
程万正、陈学忠、乔慧珍等,2006b,四川地震辐射能量和视应力的研究,地球物理学进展,21(3),692～699。
程万正、阮祥、张致伟,2009,汶川8.0级地震序列及震型判定,29(1),15～25。
成尔林、李桂芳、陈和川等,1982.1976年四川省松潘—平武7.2级地震前后主压应力轴的方向特征,地震学报,4(2),15～19。
阚荣举、刘祖荫、王绍晋等,1983,龙陵地区大震前后平均应力轴取向的时间变化,地球物理学报,26(6),38～41。
胡新亮、刁桂苓、马瑾等,2004,利用数字地震记录的,振幅比资料测定小震震源机制解的可靠性分析,地震地质,26(2),347～353。
华祥文,1980,唐山强震前后北京、天津周围地区应力场的变化过程,地震学报,2(2),33～37。
江在森、方颖、武艳强等,2009,汶川8.0级地震前区域地壳运动与变形动态过程,地球物理学报,52(2),505～518。
梁尚鸿、李幼铭、束沛镒等,1984、利用区域地震台网、振幅比资料测定小震震源参数,地球物理学报,27(3),247～257。
马瑾、刘力强、马胜利等,1995,复杂构造应力扰动场与发震构造识别问的研究,地震地质,7(4),372～382。
阮祥、程万正,2008,云南鲁甸3次MS≥5.0地震破裂参数的研究.地震学报,30(1),97～102。
万永革,2008,美国Landers地震和Hector Mine地震前震源机制与主震机制一致现象的研究,中国地震,24(3),216～225。
王绍晋、付虹、卫爱民等,2001,川滇地区7级大震前中强震震源机制变化,地震研究,24(2),88～108。
王凯英、马瑾、顾国华等,2003,1996年川滇地区发生的一次应力转向事件,地学前缘,10(特刊),233～239。
许忠淮、刘玉芳、张郢珍,1979,京津唐张地区地震应力场的方向特征,地震学报,1(2),13～18。
钟继茂、程万正,2006,由多个地震震源机制解求川滇地区平均应力场,地震学报,28(4),337～346。
赵根模、楮宝珑、郭瑞芝,1984,宁河6.9级强震前小震主=应力轴取向的变化,地震学报,6(4),414～424。
张永久、彭立国、程万正,2006,马尔康地震序列震源参数研究,中国地震,22(1),85～93。
张永久、程万正,2007,用P、S波速度振幅比求小震机制解的可行性研究,中国地震,23(4),366～374。
张致伟、程万正、阮祥等,2009,汶川8.0级地震前龙门山断裂带的地震活动性和构造应力场特征,地震学报,31(2),117～127。
Aki,K.1966.Generation and propagation of G waves from the Niigata earthquake of June16,1964,estimation of earthquakemoment,released energy,and stress-strain drop from G wave spectrum,Bulletin of the Earthquake Research Institute,44,23～88.
Chen,X.Z.,Wang,X.P.,Wang,L.Y.,et al,2003.possibility of earlier judgement on seismic tendency after strong earthquakesupon their apparent stresses,Recent Developments in World Seismology.Serial,295(7),1～5.
Kanamori H.and Heaton T.H.,2001,Microscopic and macroscopic physics of earthquakes,GeoComplexity and the Physics ofEarthquakes,147～163.
Kanamori H.,2001.Energy budget of earthquakes and seismic efficiency.Earthquake Thermodynamics and Phase Transformationsin the Earth's Interior,76,293～305.
Rydelek,P,A,.and Sacks,I,S.1999,Large earthquake occurrence affected by small stress changes,Bull Seism Soc Am.89(3),822～828.
Snoke J.A.,Munsey J.W.,Teague A.C.,et al.1984,A program for focal mechanism determination by combined use of polarityand SV-P amplitude ratio data,Earthquake Notes,55(3),121～128.
Sadovsky,M A.1972,The processes preceding strong earthquakes in some regions of Middle Asian,Tectonophysics,14(3/4),116～l25.
Sadovsky M A.Nersesov I L,1974,Ferecasts of earthquakes on the basis of complex geophysical features,Tectonophysics,23(3),135～142.
Seeber L,Armbruster J G.,2000,Earthquakes as beacons of stress change,Nature,407,69～72.
Wyss,M.and Brune,J.N.,1968,Seismic moment,stress,and source dimensions for earthquakes in the California-Nevadaregion,J.Geophys.Res.,73,4681～4694.
Wyss,M.,1970a,Apparent stresses of earthquakes on ridges compared to apparent stresses of earthquakes in trenches.Geophys,J.R.astr.Soc.,19,479～484.
Wyss,M,1970b,Stress estimates for South American shallow and deep earthquakes,J.Geophys.Res.,75(8),1529～1544.
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