2008年汶川M_S8.0地震前地震活动异常特征
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摘要
分析了汶川地震前地震活动时空演化特征.结果表明:①汶川地震前38a龙门山断裂带及其附近形成5级地震背景空区,震前6.5a形成ML4.0地震孕震空区,震前1a孕震空区内部及其两端相继发生多次ML4.0—5.0地震,空区缩小;②中国大陆西部及邻区2001年以来处于大震活跃时段,而中国大陆内部地震活动水平非常低,出现非常显著的7级、6级和5级地震平静;③南北地震带7级以上地震在时间上具有准周期特征,空间上存在由南向北迁移的特点,汶川地震的发生符合这一规律;④1988年以来南北地震带中段为7级地震空段,汶川地震就发生该空段内;⑤2003年云南大姚地震后,南北地震带地震活动显著增强,且在中、南段形成4.6级以上地震环形分布,四川及其附近表现为异常平静,同时震群活动显著,且在4.6级地震平静区内形成震群空区,汶川地震就发生震群空区的边缘,震前8个月,震群频度出现高值异常;⑥汶川地震前7个月,青藏块体大范围ML≥4.0地震平静103d,2008年1月13日以后平静区逐渐解体,至汶川地震前4级地震平静区缩小到巴颜喀拉地块,汶川地震就发生在巴颜喀拉地块的东边界带上,汶川地震前3个多月,孕震空区内部出现NW走向的3级地震条带,与龙门山断裂带斜交.
The spatio-temporal evolution characteristics of seismic activity before 2008 Wenchuan MS8.0 earthquake are studied.Some results are as follows:① A background gap of M≥5.0 earthquakes formed in the area of Longmenshan fault zone and its vicinity 38 years before the 2008 Wenchuan earthquake.A seismogenic gap of ML≥4.0 earthquakes appeared in the same area 6.5 years prior to the Wenchuan earthquake.It is noticed that one year before the Wenchuan earthquake some particular earthquakes with ML4.0—5.0 occurred successively in Longmenshan fault zone and its two end regions,and the original gap was reduced.② Western China mainland and its adjacent area has been in the seismically active period since 2001,while the inner land of China is seismically inactive,with remarkable quiescence of M≥7.0,M≥6.0 and M≥5.0 earthquakes.③ The activity of M≥7.0 earthquakes in the South--North Seismic Zone showed temporally quasi-cyclic variation and spatial migration from south to north.The occurrence of the Wenchuan earthquake itself followed this feature.④ A quiescence area of M≥7.0 earthquakes formed in the middle and northern part of the South--North Seismic Zone since 1988 and the Wenchuan earthquake occurred in it.⑤ The seismic activity obviously strengthened and a doughnut-shape pattern of M≥4.6 earthquakes appeared in the middle and southern part of the South--North Seismic Zone after the 2003 Dayao,Yunnan,earthquake.Sichuan province and its vicinity in the middle of the doughnut-shape pattern were obviously quiescent.In the same time,earthquake swarms were often seen and showed heterogeneous temporal and spatial distribution.A swarm gap appeared in the quiet area of M4.6 earthquakes and the Wenchuan earthquake occurred just on the margin of the gap.Earthquake swarms occurred quite frequently during the 8 months before Wenchuan earthquake.⑥ Quiescence of ML≥4.0 earthquakes appeared in Qinghai--Xizang block 7 months before Wenchuan earthquake and the quiescence state gradually disappeared since 13 January 2008.Before the Wenchuan earthquake the quiescence area reduced to the region of Bayankala block and the Wenchuan mainshock occurred just in eastern boundary zone of the block.A belt of ML≥3.0 earthquakes striking in NW--SE direction,which obliquely crosses to the Longmenshan fault zone,formed 3 months before the Wenchuan earthquake in the seismogenic gap.
The spatio-temporal evolution characteristics of seismic activity before 2008 Wenchuan MS8.0 earthquake are studied.Some results are as follows:① A background gap of M≥5.0 earthquakes formed in the area of Longmenshan fault zone and its vicinity 38 years before the 2008 Wenchuan earthquake.A seismogenic gap of ML≥4.0 earthquakes appeared in the same area 6.5 years prior to the Wenchuan earthquake.It is noticed that one year before the Wenchuan earthquake some particular earthquakes with ML4.0—5.0 occurred successively in Longmenshan fault zone and its two end regions,and the original gap was reduced.② Western China mainland and its adjacent area has been in the seismically active period since 2001,while the inner land of China is seismically inactive,with remarkable quiescence of M≥7.0,M≥6.0 and M≥5.0 earthquakes.③ The activity of M≥7.0 earthquakes in the South--North Seismic Zone showed temporally quasi-cyclic variation and spatial migration from south to north.The occurrence of the Wenchuan earthquake itself followed this feature.④ A quiescence area of M≥7.0 earthquakes formed in the middle and northern part of the South--North Seismic Zone since 1988 and the Wenchuan earthquake occurred in it.⑤ The seismic activity obviously strengthened and a doughnut-shape pattern of M≥4.6 earthquakes appeared in the middle and southern part of the South--North Seismic Zone after the 2003 Dayao,Yunnan,earthquake.Sichuan province and its vicinity in the middle of the doughnut-shape pattern were obviously quiescent.In the same time,earthquake swarms were often seen and showed heterogeneous temporal and spatial distribution.A swarm gap appeared in the quiet area of M4.6 earthquakes and the Wenchuan earthquake occurred just on the margin of the gap.Earthquake swarms occurred quite frequently during the 8 months before Wenchuan earthquake.⑥ Quiescence of ML≥4.0 earthquakes appeared in Qinghai--Xizang block 7 months before Wenchuan earthquake and the quiescence state gradually disappeared since 13 January 2008.Before the Wenchuan earthquake the quiescence area reduced to the region of Bayankala block and the Wenchuan mainshock occurred just in eastern boundary zone of the block.A belt of ML≥3.0 earthquakes striking in NW--SE direction,which obliquely crosses to the Longmenshan fault zone,formed 3 months before the Wenchuan earthquake in the seismogenic gap.
引文
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徐锡伟,张培震,闻学泽,秦尊丽,陈桂华,朱艾斓.2005.川西及其邻近地区活动构造基本特征与强震复发模型[J].地震地质,27(3):446--461.
徐锡伟,闻学泽,陈桂华,于桂华.2008.巴颜喀拉地块东部龙日坝断裂带的发现及其大地构造意义[J].中国科学,38(5):529--542.
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张培震,徐锡伟,闻学泽,冉勇康.2008.汶川8.0级地震发震断裂带的滑动速率、复发周期和构造成因[J].地球物理学报,51(4):1066--1073.
张培震,邓起东,张国民,马瑾,甘卫军,闵伟,毛凤英,王琪.2003.中国大陆的强震活动与活动地块[J].中国科学:D辑,33(增刊):12--20.
中国地震局震害防御司.1999.中国近代地震目录(公元1912年—1990年MS≥4.7)[M].北京:中国科学技术出版社:1--637.
中国地震台网中心.2007.2008年度我国地震趋势研究报告:中国地震趋势预测研究(2008年度)[M].北京:地震出版社:1--121.
Densemore A L,Ellis M,Li Y.2007.Active tectonics of the Beichuan and Pengguan faults at the eastern margin of theTibetan Plateau[J].Tectonics,26:TC4005,doi:10.1029/2006TC001987.
傅征祥,金学申,邵辉成,丁香.2005.中国大陆强地震成组活动迁移及其机理分析[J].地震,25(4):65--74.
国家地震局震害防御司.1995.中国历史强震目录(公元前23世纪—1911年)[J].北京:地震出版社:1--514.
黄玮琼,李文香,曹学锋.1994.中国大陆地震资料完整性研究之二:分区地震资料基本完整的起始年分布图象[J].地震学报,16(4):423--432.
姜秀娥,陈非比.1983.区域震群与唐山大震[J].地震学报,5(2):146--156.
李钦祖,于利民,王吉易,万迪堃,陈绍绪.1993.中国大陆强地震的成组活动和概率预报[J].中国科学:B辑,23(5):519--526.
李钦祖,于立民,王吉易,万迪堃,陈绍绪.1994.成组活动是中国大陆强地震的一个基本特点[J].地震学报,6(1):1--17.
陆远忠,沈建文,宋俊高.1982.孕震空区与逼近地震[J].地震学报,4(4):327--336.
陆远忠,王炜,沈建文.1983.孕震空区与逼近地震(续)[J].地震学报,5(2):129--144.
梅世蓉.1960.中国的地震活动性[J].地球物理学报,9(1):1--19.
梅世蓉,宋志平,薛艳.1996.中国巨大地震前地震活动环形分布图象与规律[J].地震学报,18(4):413--419.
王俊国,王林瑛,吴晓芝,陈佩燕,白彤霞,何巧云.2004.华北地区强震前的信号震及其预测意义[J].地震,24(3):51--60.
徐锡伟,张培震,闻学泽,秦尊丽,陈桂华,朱艾斓.2005.川西及其邻近地区活动构造基本特征与强震复发模型[J].地震地质,27(3):446--461.
徐锡伟,闻学泽,陈桂华,于桂华.2008.巴颜喀拉地块东部龙日坝断裂带的发现及其大地构造意义[J].中国科学,38(5):529--542.
薛艳,梅世蓉.1999.唐山大震前一般震群与前兆震群时空演化特征研究[J].地震,19(2):184--189.
张勇,冯万鹏,许力生,周成虎,陈运泰.2008.2008年汶川大地震的时空破裂过程[J].中国科学:D辑,38(10):1186--1194.
张培震,徐锡伟,闻学泽,冉勇康.2008.汶川8.0级地震发震断裂带的滑动速率、复发周期和构造成因[J].地球物理学报,51(4):1066--1073.
张培震,邓起东,张国民,马瑾,甘卫军,闵伟,毛凤英,王琪.2003.中国大陆的强震活动与活动地块[J].中国科学:D辑,33(增刊):12--20.
中国地震局震害防御司.1999.中国近代地震目录(公元1912年—1990年MS≥4.7)[M].北京:中国科学技术出版社:1--637.
中国地震台网中心.2007.2008年度我国地震趋势研究报告:中国地震趋势预测研究(2008年度)[M].北京:地震出版社:1--121.
Densemore A L,Ellis M,Li Y.2007.Active tectonics of the Beichuan and Pengguan faults at the eastern margin of theTibetan Plateau[J].Tectonics,26:TC4005,doi:10.1029/2006TC001987.
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