小江断裂中段及其邻近地区应力场时间变化分析
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摘要
研究地壳构造应力状态及其时空分布特征,特别是应力变化的信息,是探讨地震成因、分析发震条件的重要有效途径之一.本文利用1998年1月至2009年1月以来小江断裂中段及其邻区ML≥2.5的共计740个震源机制解,基于小江断裂中段及其邻近地区地质构造背景,对研究区进行了分区;以该区域内较大地震为界,结合余震时间序列特征,进行时间上的分段;去除较大地震后,采用最长距离聚类分析方法对各分区的地震进行了分类.在此基础上,利用Gephart的应力张量反演方法,根据震源机制解资料反演出了各分区的优势应力场.结果表明,在观测时段内,根据构造和震源机制,可将研究区域分为A和B两个区域.A区最大主应力σ1方位在4个时段内大致为NNW向,B区北部在4个时段内σ1方位大致为NNW向、WNW和ENE向.从应力结构看,A区和B区北部应力以水平作用为主.B区南部σ1方位大致为NNW向,仍以水平作用为主;B区北部σ1方位变化较大,可能与B区北部地质结构复杂、应力调整活跃有关.而A区主应力方位相对稳定,显示了滇中块体的稳定性.
The study on temporal and spatial crustal stress change is important for exploring earthquake origin and seismogenic condition.Based on 740 focal mechanism solutions of ML≥2.5 earthquakes occurred during Jan.1998 to Jan.2009 in middle Xiaojiang fault and its adjacent area,the studied region was divided into sub-regions,and temporally further divided into phases with the larger earthquakes as boundary of the sub-regions.After removal of the larger earthquakes this paper inverted the focal mechanism data with the method of Gephart for the stress in main phase of each sub-region.The result indicates that the azimuth of maximum principal stress σ1 in 4 temporal phases of the sub-region A is approximately NNW--SSE,and in northern part of sub-region B are approximately NNW--SSE,WNW--ESE and ENE--WSW.The azimuth of σ1 in southern part of sub-region B is approximately NNW-SSE.The azimuth of σ1 in northern part of sub-region B changed significantly,while the azimuth of σ1 in sub-region A is relatively stable.This result may be related to the complicated structure and possible stress adjusting in northern sub-region B.The σ1 directions in sub-region A may indicate seismically relative stability of the central Yunnan crustal block.
The study on temporal and spatial crustal stress change is important for exploring earthquake origin and seismogenic condition.Based on 740 focal mechanism solutions of ML≥2.5 earthquakes occurred during Jan.1998 to Jan.2009 in middle Xiaojiang fault and its adjacent area,the studied region was divided into sub-regions,and temporally further divided into phases with the larger earthquakes as boundary of the sub-regions.After removal of the larger earthquakes this paper inverted the focal mechanism data with the method of Gephart for the stress in main phase of each sub-region.The result indicates that the azimuth of maximum principal stress σ1 in 4 temporal phases of the sub-region A is approximately NNW--SSE,and in northern part of sub-region B are approximately NNW--SSE,WNW--ESE and ENE--WSW.The azimuth of σ1 in southern part of sub-region B is approximately NNW-SSE.The azimuth of σ1 in northern part of sub-region B changed significantly,while the azimuth of σ1 in sub-region A is relatively stable.This result may be related to the complicated structure and possible stress adjusting in northern sub-region B.The σ1 directions in sub-region A may indicate seismically relative stability of the central Yunnan crustal block.
引文
程万正,刁桂苓,吕弋培,张永久,李桂芳,陈天长.2003.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,25(1):71-87.
崔效锋,谢富仁,张红艳.2006.川滇地区现代构造应力场分区及动力学意义[J].地震学报,28(5):451-461.
刁桂苓,于利民,李钦祖.1992.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,8(3):86-92.
刁桂苓,于利民,宁杰远,孙佩卿,张子广.1993.1989年大同震群的体破裂特征[J].地球物理学报,36(3):360-368.
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阚荣举,张四昌,晏凤桐.1977.我国西南地区现代构造应力场与现代构造活动特征的探讨[J].地球物理学报,20(2):96-109.
阚荣举.1980.西南地区现代构造应力场与板内强震活动[J].地震研究,3(3):45-59.
胡新亮,刁桂苓,马瑾,李雪英,高景春,王勤彩.2004.利用数字地震记录的珚P,S珔振幅比资料测定小震震源机制解的可靠性分析[J].地震地质,26(2):347-352.
李坪,汪良谋.1975.云南川西地区地震地质基本特征的探讨[J].地质科学,(4):308-325.
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林向东,徐平,武敏捷,武安绪.2010.小江断裂中段及邻区构造应力场分布特征[J].中国地震,26(2):192-200.
王绍晋,龙晓帆,余庆坤.2005.昆明地区现代构造应力场分析[J].地震研究,28(2):178-184.
许忠淮,阎明,赵仲和.1983.由多个小地震推断的华北地区构造应力场的方向[J].地震学报,5(3):268-279.
许忠淮,汪素云,黄雨蕊,高阿甲,金小锋,常向东.1987.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[J].地球物理学报,30(5):476-486.
谢富仁,苏刚,崔效锋.2001.滇西南地区现代构造应力场分析[J].地震学报,23(1):17-23.
Chen Y,Li L,Li J,Li G.2008.Wenchuan earthquake:Way of thinking is changed[J].Episodes,31:374-377.
Castillo,D A,Zoback M D.1995.Systematic stress variations in the southern San Joaquin Valley and along the WhiteWolf Fault:Implications for the rupture mechanics of the1952MS7.8Kern County earthquake and contemporarySeismicity[J].J Geophys Res,100:6249-6264.
Dreger D,Savage B.1999.Aftershocks of the1952Kern County,California,earthquake sequence[J].Bull Seism SocAmer,89(4):1094-1108.
Gephart J W.1990.FMSI:A Fortran program for inverting fault/slickenside and earthquake focal mechanism data to ob-tain the regional stress tensor[J].Computer&Geoscience,16(7):953-989.
Hauksson E,Jones L M,Hutton K.1995.The1994Northridge earthquake sequence in California:Seismological andtectonic aspects[J].J Geophys Res,100:12335-12355.
Lin X D,Xu P,Wu M J,Wu A X.2011.Inversion of stress fields in the middle section of the Xiaojiang fault and its ad-jacent area[J].Earthquake Research in China,25(1):82-91.
Oppenheimer D H.1990.Aftershock slip behavior of the1989Loma Prieta,California,earthquake[J].Geophy ReshLett,17(8):1199-1202.
崔效锋,谢富仁,张红艳.2006.川滇地区现代构造应力场分区及动力学意义[J].地震学报,28(5):451-461.
刁桂苓,于利民,李钦祖.1992.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,8(3):86-92.
刁桂苓,于利民,宁杰远,孙佩卿,张子广.1993.1989年大同震群的体破裂特征[J].地球物理学报,36(3):360-368.
邓起东.2007.中国活动构造图(1∶400万)[M].北京:地震出版社:1.
阚荣举,张四昌,晏凤桐.1977.我国西南地区现代构造应力场与现代构造活动特征的探讨[J].地球物理学报,20(2):96-109.
阚荣举.1980.西南地区现代构造应力场与板内强震活动[J].地震研究,3(3):45-59.
胡新亮,刁桂苓,马瑾,李雪英,高景春,王勤彩.2004.利用数字地震记录的珚P,S珔振幅比资料测定小震震源机制解的可靠性分析[J].地震地质,26(2):347-352.
李坪,汪良谋.1975.云南川西地区地震地质基本特征的探讨[J].地质科学,(4):308-325.
梁尚鸿,李幼铭,束沛镒,朱碚定.1984.利用区域地震台网P、S振幅比资料测定小震震源参数[J].地球物理学报,27(3):249-257.
林向东.2009.小江断裂中段及其邻近地区震源机制解与构造应力场分析[D].兰州:中国地震局兰州地震研究所:37-38.
林向东,徐平,武敏捷,武安绪.2010.小江断裂中段及邻区构造应力场分布特征[J].中国地震,26(2):192-200.
王绍晋,龙晓帆,余庆坤.2005.昆明地区现代构造应力场分析[J].地震研究,28(2):178-184.
许忠淮,阎明,赵仲和.1983.由多个小地震推断的华北地区构造应力场的方向[J].地震学报,5(3):268-279.
许忠淮,汪素云,黄雨蕊,高阿甲,金小锋,常向东.1987.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[J].地球物理学报,30(5):476-486.
谢富仁,苏刚,崔效锋.2001.滇西南地区现代构造应力场分析[J].地震学报,23(1):17-23.
Chen Y,Li L,Li J,Li G.2008.Wenchuan earthquake:Way of thinking is changed[J].Episodes,31:374-377.
Castillo,D A,Zoback M D.1995.Systematic stress variations in the southern San Joaquin Valley and along the WhiteWolf Fault:Implications for the rupture mechanics of the1952MS7.8Kern County earthquake and contemporarySeismicity[J].J Geophys Res,100:6249-6264.
Dreger D,Savage B.1999.Aftershocks of the1952Kern County,California,earthquake sequence[J].Bull Seism SocAmer,89(4):1094-1108.
Gephart J W.1990.FMSI:A Fortran program for inverting fault/slickenside and earthquake focal mechanism data to ob-tain the regional stress tensor[J].Computer&Geoscience,16(7):953-989.
Hauksson E,Jones L M,Hutton K.1995.The1994Northridge earthquake sequence in California:Seismological andtectonic aspects[J].J Geophys Res,100:12335-12355.
Lin X D,Xu P,Wu M J,Wu A X.2011.Inversion of stress fields in the middle section of the Xiaojiang fault and its ad-jacent area[J].Earthquake Research in China,25(1):82-91.
Oppenheimer D H.1990.Aftershock slip behavior of the1989Loma Prieta,California,earthquake[J].Geophy ReshLett,17(8):1199-1202.
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