秦岭—大别东段应力状态研究
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摘要
本文首先通过Snoke发展的利用P波、 SV波和SH波的初动和振幅比方法计算秦岭—大别东段2008年以来83次M_L≥2.5地震的震源机制解,然后通过FMSI方法反演得到平均应力场的方向特征:近东西向的水平挤压和近南北向的水平拉张作用,与参数统计结果一致;进而通过震源机制的一致性参数分析应力场方向的变化信息。分析表明震源机制解呈现了由变化紊乱、偏离平均应力场到变化一致、趋于平均应力场再到变化紊乱、偏离平均应力场的变化过程,在显著地震前,研究区整体的震源机制一致性参数处于持续低值状态;计算了2008年以来93次M_L≥2.5地震的视应力,拟合视应力与震级的关系,分析扣除震级影响的差视应力随时间变化特征,近似反映研究区应力大小的变化。分析表明显著地震前研究区的差视应力值呈现出明显的先上升后下降的变化过程,在下降过程中发生地震;最后利用震源机制一致性参数和差视应力综合分析研究区的应力状态,均表明显著地震前震源区的构造应力场增强。目前研究区的震源机制一致性参数较高、差视应力较低,研究区的应力水平较低。
Through the method developed by Snoke, which uses the ratio of initial motion and amplitude of P, SV and SH waves, we calculated the focal mechanism solution to 83 M_L≥2.5 earthquakes since 2008 in eastern Qinling—Dabie region. Based on these focal mechanisms, we inverted direction characteristic of the mean stress field using the FMSI method. The result shows that Qinling—Dabie eastern region is horizontally compressed in nearly E-W direction and horizontally dilated in nearly N-S direction, which is in accord with statistical results of focal mechanism parameters. We analyzed the variation information of the mean stress field direction through the consistency parameter of focal mechanisms, and the result shows that the focal mechanisms show a process from change in disorder and deviation from the mean stress field, to change in order and tendency to the mean stress field, then to change in disorder and deviation from the mean stress field. Consistency parameter of focal mechanisms in the studied region was in a continuous low value state before the significant earthquakes. Moreover, we calculated the apparent stress of 93 M_L≥2.5 earthquakes since 2008 in Qinling—Dabie eastern region, and fitted the relationship between apparent stress and magnitude, analyzed the time variation characteristic of the difference apparent stress that eliminated the effect of magnitude and reflected the variation of stress magnitude in the study area. The result shows that apparent stress in studied region showed a distinct process of first rising and then decreasing before significant earthquakes, and the significant earthquakes occurred during the process of decreasing. Finally, we analyzed the stress state in the study region by using consistency parameter of focal mechanism and difference apparent stress, and the result showed that regional stress field enhanced apparently before significant earthquakes. At present, the consistency parameter of focal mechanism in the study area is high, and difference apparent stress is low, so the regional stress level is low.
Through the method developed by Snoke, which uses the ratio of initial motion and amplitude of P, SV and SH waves, we calculated the focal mechanism solution to 83 M_L≥2.5 earthquakes since 2008 in eastern Qinling—Dabie region. Based on these focal mechanisms, we inverted direction characteristic of the mean stress field using the FMSI method. The result shows that Qinling—Dabie eastern region is horizontally compressed in nearly E-W direction and horizontally dilated in nearly N-S direction, which is in accord with statistical results of focal mechanism parameters. We analyzed the variation information of the mean stress field direction through the consistency parameter of focal mechanisms, and the result shows that the focal mechanisms show a process from change in disorder and deviation from the mean stress field, to change in order and tendency to the mean stress field, then to change in disorder and deviation from the mean stress field. Consistency parameter of focal mechanisms in the studied region was in a continuous low value state before the significant earthquakes. Moreover, we calculated the apparent stress of 93 M_L≥2.5 earthquakes since 2008 in Qinling—Dabie eastern region, and fitted the relationship between apparent stress and magnitude, analyzed the time variation characteristic of the difference apparent stress that eliminated the effect of magnitude and reflected the variation of stress magnitude in the study area. The result shows that apparent stress in studied region showed a distinct process of first rising and then decreasing before significant earthquakes, and the significant earthquakes occurred during the process of decreasing. Finally, we analyzed the stress state in the study region by using consistency parameter of focal mechanism and difference apparent stress, and the result showed that regional stress field enhanced apparently before significant earthquakes. At present, the consistency parameter of focal mechanism in the study area is high, and difference apparent stress is low, so the regional stress level is low.
引文
[1] Zoback M L.First and second-order patterns of stress in the lithosphere:The world stress map project[J].J Geophys Res,1992,97(B8):11703-11728.
[2] Chen Y,Li L,Li J,et al.Wenchuan earthquake:Way of thinking is changed[J].Episodes,2008,31:374-377.
[3] 王清晨,孙枢,李继亮,等.秦岭的大地构造演化[J].地质科学,1989,2:129-142.
[4] 张毅,陈宇卫,黄显良,等.东大别山构造带六安-英山地磁剖面观测与地震研究[J].地球物理学进展,2013,28(1):207-213,doi:10.6038/pg20130122.
[5] 李钦祖,王泽皋,贾云年,等.由单台小地震资料所得两个区域的应力场[J].地球物理学报,1973,16(1):49-61.
[6] 夏瑞良.安徽区域地震应力场的分布特征[J].地震地质,1985,7(3):13-21.
[7] 刁桂苓,于利民,李钦祖.震源机制解的系统聚类分析——以海城地震序列为例[J].中国地震,1992,8(3):86-92.
[8] 刘东旺,刘泽民,沈小七,等.安徽淮河构造变形带及邻近块体现代构造应力场特征[J].中国地震,2004,20(4):364-371.
[9] 刘泽民,刘东旺,李玲利,等.利用多个震源机制解求东大别地区平均应力场[J].地震学报,2011,33(5):605-613.
[10] Snoke J A,Munsey J W,Teague A G,et al.A program for focal mechanism determination by combined use of polarity and SV-P amplitude ratio data[J].Earthquake Notes,1984,55(3):15-20.
[11] 倪红玉,刘泽民,沈小七,等.利用FOCMEC方法震源机制解的影响因素分析[J].华北地震科学,2011,29(3):1-7.
[12] 倪红玉,沈小七,洪德全,等.2014年金寨ML3.9震群序列特征研究[J].地震学报,2015,37(6):925-936.
[13] Michael A J.Determination of stress from slip data:faults and folds[J].J.Geophy.Res,1984,89:11517-11526.
[14] 许忠淮.用滑动方向拟合法反演唐山余震区的平均应力场[J].地震学报,1985,7(4):349-361.
[15] Gephart J W,Forsyth D W.An improved method for determining the regional stress tensor using focal mechanism data:Application to the San Fernando earthquakesequence[J].J Geophys Res,1984,89(B11):9305-9320.
[16] Angelier J.Inversion of earthquake focal mechanisms to obtain the seismotectonic stress IV—a new method free of choice among nodal planes[J].Geophys.J.Int.,2002,150(3):588-609.
[17] 钟继茂,程万正.由多个地震震源机制解求川滇地区平均应力场方向[J].地震学报,2006,28(4):337-346.
[18] 陈颙.用震源机制一致性作为描述地震活动性的新参数[J].地球物理学报,1978,21(2):142-159.
[19] 程万正,阮祥,张永久.川滇次级地块震源机制解类型与一致性参数[J].地震学报,2006,28(6):561-573.
[20] 吴忠良,黄静,林碧苍.中国西部地震视应力的空间分布[J].地震学报,2002,24(3):293-301.
[21] 中国地震局监测预报司.测震学原理与方法[M].北京:地震出版社,2017:453-457.
[22] 戚浩,夏仕安,张炳,等.安徽地区震源参数特征研究[J].内陆地震,2012,26(3):257-262.
[23] 陈学忠,李艳娥.2006年7月4日河北文安MS5.1地震前震中周围地区小震视应力随时间的变化[J].中国地震,2007,23(4):327-336.
[24] Archuleta R,Cranswick E,Mueller C,et al.Source parameters of the 1980 Mammoth Lakes,California earthquake sequence[J].Journal of Geophysical Research Atmospheres,1982,87(NB6):4595-4607.
[25] 程万正,刁桂苓,吕弋培,等.川滇地块的震源力学机制、 运动速率和活动方式[J].地震地质,2003,25(1):71-87.
[26] 倪红玉,刘泽民,洪德全,等.“霍山窗”地区现代构造应力场研究[J].中国地震,2012,28(3):294-303.
[27] 倪红玉,刘泽民,洪德全,等.综合研究2014年霍山MS4.3地震序列的震源机制变化过程[J].地震地质,2015,37(4):1004-1019.
[28] 黄显良,刘泽民,郁建芳,等.2014年金寨MS3.4级震群序列震源一致性研究[J].地震学报,2015,37(6):916-924.
[29] 李艳娥,陈学忠,王恒信.汶川8.0级地震前四川地区地震视应力时空变化特征[J].地震,2012,32(4):113-122.
[30] 岳晓媛,武安绪,冯刚,等.2012年河北唐山MS4.8地震前首都圈东部视应力时空变化特征[J].地震,2015,35(2):90-100.
[31] 付虹,王邵晋,李丽,等.滇中地区震源机制一致性参数时空分布与强震活动[J].地震研究,2011,34(2):113-118.
[2] Chen Y,Li L,Li J,et al.Wenchuan earthquake:Way of thinking is changed[J].Episodes,2008,31:374-377.
[3] 王清晨,孙枢,李继亮,等.秦岭的大地构造演化[J].地质科学,1989,2:129-142.
[4] 张毅,陈宇卫,黄显良,等.东大别山构造带六安-英山地磁剖面观测与地震研究[J].地球物理学进展,2013,28(1):207-213,doi:10.6038/pg20130122.
[5] 李钦祖,王泽皋,贾云年,等.由单台小地震资料所得两个区域的应力场[J].地球物理学报,1973,16(1):49-61.
[6] 夏瑞良.安徽区域地震应力场的分布特征[J].地震地质,1985,7(3):13-21.
[7] 刁桂苓,于利民,李钦祖.震源机制解的系统聚类分析——以海城地震序列为例[J].中国地震,1992,8(3):86-92.
[8] 刘东旺,刘泽民,沈小七,等.安徽淮河构造变形带及邻近块体现代构造应力场特征[J].中国地震,2004,20(4):364-371.
[9] 刘泽民,刘东旺,李玲利,等.利用多个震源机制解求东大别地区平均应力场[J].地震学报,2011,33(5):605-613.
[10] Snoke J A,Munsey J W,Teague A G,et al.A program for focal mechanism determination by combined use of polarity and SV-P amplitude ratio data[J].Earthquake Notes,1984,55(3):15-20.
[11] 倪红玉,刘泽民,沈小七,等.利用FOCMEC方法震源机制解的影响因素分析[J].华北地震科学,2011,29(3):1-7.
[12] 倪红玉,沈小七,洪德全,等.2014年金寨ML3.9震群序列特征研究[J].地震学报,2015,37(6):925-936.
[13] Michael A J.Determination of stress from slip data:faults and folds[J].J.Geophy.Res,1984,89:11517-11526.
[14] 许忠淮.用滑动方向拟合法反演唐山余震区的平均应力场[J].地震学报,1985,7(4):349-361.
[15] Gephart J W,Forsyth D W.An improved method for determining the regional stress tensor using focal mechanism data:Application to the San Fernando earthquakesequence[J].J Geophys Res,1984,89(B11):9305-9320.
[16] Angelier J.Inversion of earthquake focal mechanisms to obtain the seismotectonic stress IV—a new method free of choice among nodal planes[J].Geophys.J.Int.,2002,150(3):588-609.
[17] 钟继茂,程万正.由多个地震震源机制解求川滇地区平均应力场方向[J].地震学报,2006,28(4):337-346.
[18] 陈颙.用震源机制一致性作为描述地震活动性的新参数[J].地球物理学报,1978,21(2):142-159.
[19] 程万正,阮祥,张永久.川滇次级地块震源机制解类型与一致性参数[J].地震学报,2006,28(6):561-573.
[20] 吴忠良,黄静,林碧苍.中国西部地震视应力的空间分布[J].地震学报,2002,24(3):293-301.
[21] 中国地震局监测预报司.测震学原理与方法[M].北京:地震出版社,2017:453-457.
[22] 戚浩,夏仕安,张炳,等.安徽地区震源参数特征研究[J].内陆地震,2012,26(3):257-262.
[23] 陈学忠,李艳娥.2006年7月4日河北文安MS5.1地震前震中周围地区小震视应力随时间的变化[J].中国地震,2007,23(4):327-336.
[24] Archuleta R,Cranswick E,Mueller C,et al.Source parameters of the 1980 Mammoth Lakes,California earthquake sequence[J].Journal of Geophysical Research Atmospheres,1982,87(NB6):4595-4607.
[25] 程万正,刁桂苓,吕弋培,等.川滇地块的震源力学机制、 运动速率和活动方式[J].地震地质,2003,25(1):71-87.
[26] 倪红玉,刘泽民,洪德全,等.“霍山窗”地区现代构造应力场研究[J].中国地震,2012,28(3):294-303.
[27] 倪红玉,刘泽民,洪德全,等.综合研究2014年霍山MS4.3地震序列的震源机制变化过程[J].地震地质,2015,37(4):1004-1019.
[28] 黄显良,刘泽民,郁建芳,等.2014年金寨MS3.4级震群序列震源一致性研究[J].地震学报,2015,37(6):916-924.
[29] 李艳娥,陈学忠,王恒信.汶川8.0级地震前四川地区地震视应力时空变化特征[J].地震,2012,32(4):113-122.
[30] 岳晓媛,武安绪,冯刚,等.2012年河北唐山MS4.8地震前首都圈东部视应力时空变化特征[J].地震,2015,35(2):90-100.
[31] 付虹,王邵晋,李丽,等.滇中地区震源机制一致性参数时空分布与强震活动[J].地震研究,2011,34(2):113-118.
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