大地震的发生条件
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摘要
大地震(特别是8级以上的大地震)的发生必须满足2个基本条件:一个是震源附近要有超过岩石弹性极限的高应力背景;另一个是该处的岩石具有发生地震的能力,即在大地震孕育所需的时间尺度(几千年以上)内岩石能长期保持弹性。为考察第1个条件,分析了中国周边三大板块的作用力。认为太平洋板块在海沟附近的俯冲方式所产生的水平力分量较小,而且海沟离中国大陆较远,因此它对中国的地震影响不大;菲律宾海板块对台湾的碰撞使台湾及福建沿海地区为高应力区,但由于碰撞边界的长度只有200km左右,其影响范围不大;印度板块向北推挤是产生中国西部及华北高应力区的最主要原因,文中较详细分析了它的作用,并据此尝试性划分了3个对中国具有强烈影响的地震带。根据岩石的流变性质和地质形成时代把地质体分成了刚性、次刚性和较柔性3类。初步计算了刚性地块的弹性持续时间至少在1Ma以上,而柔性地块的弹性持续时间最多为1ka。因此,8级大地震的位置与刚性地块密切相关。
Two necessary conditions for occurrence of great earthquakes,especially for MS≥8.0 ones are:The high stress which must exceeds the elastic limit of rock;and that the rock should maintain elastic behavior in a longer period than the time for strain accumulation in rock(usually several thousand years).To check the first condition,the actions of the three plates surrounding China are analyzed.The subduction zone between the Pacific plate and Asian plate is far away from the Chinese continent,and the horizontal component of the subduction force is relatively small,so there is no significant effect on China.The collision zone between the Philippine Sea plate and the Asian plate makes Taiwan and Fujian Province of China become high stress area.As the collision boundary is short(only 200km long),the stress declines rapidly along the northwest direction.The high stress area in northwest China and north China is due to the Indian plate's strong collision to Asian plate.The collision boundary between Indian plate and Asian plate is composed of three arc parts with different directions and magnitudes of force.Based on this data,we try to recognize the three seismic belts.To predict the possible locations of great earthquakes,three geologic units(rigid block,sub-rigid block and fold belt)are divided and their rheology is anayzed.Based on the calculated data,the elasticity of rigid block can maintain as long as 1million years,while there is only 1000 years for fold belt.So,the location of MS 8.0 earthquake is related closely to rigid blocks.
Two necessary conditions for occurrence of great earthquakes,especially for MS≥8.0 ones are:The high stress which must exceeds the elastic limit of rock;and that the rock should maintain elastic behavior in a longer period than the time for strain accumulation in rock(usually several thousand years).To check the first condition,the actions of the three plates surrounding China are analyzed.The subduction zone between the Pacific plate and Asian plate is far away from the Chinese continent,and the horizontal component of the subduction force is relatively small,so there is no significant effect on China.The collision zone between the Philippine Sea plate and the Asian plate makes Taiwan and Fujian Province of China become high stress area.As the collision boundary is short(only 200km long),the stress declines rapidly along the northwest direction.The high stress area in northwest China and north China is due to the Indian plate's strong collision to Asian plate.The collision boundary between Indian plate and Asian plate is composed of three arc parts with different directions and magnitudes of force.Based on this data,we try to recognize the three seismic belts.To predict the possible locations of great earthquakes,three geologic units(rigid block,sub-rigid block and fold belt)are divided and their rheology is anayzed.Based on the calculated data,the elasticity of rigid block can maintain as long as 1million years,while there is only 1000 years for fold belt.So,the location of MS 8.0 earthquake is related closely to rigid blocks.
引文
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马杏垣主编.1987.中国岩石圈动力学纲要[M].北京:地质出版社.p.66.MA Xing-yuan(ed).1987.Outline of Lithospheric Dynamics in China[M].Geologic Publishing House,Beijing(inChinese).
袁学诚主编.1996.中国地球物理图集[Z].北京:地质出版社.YUAN Xue-cheng(ed).1996.Geophysics Atlas in China[Z].Geologic Publishing House,Beijing(in Chinese).
张培震,徐锡伟,闻学泽,等.2008.2008年汶川8.0级地震发震断裂的滑动速率、复发周期和构造成因[J].地球物理学报,51(4):1066—1073.ZHANG Pei-zhen,XU Xi-wei,WEN Xue-ze,et al.2008.Slip rates and recurrence intervals of the Longmenshan activefault zone,and tectonic implication for the mechanism of the May12Wenchuan earthquake,2008,Sichuan,China[J].Chinese Journal of Geophsics,51(4):1066—1073(in Chinese).
Allen T.PAGER-CAT[DB/OL].http:∥earthquake.usgs.gov/research/data/pager/.2008.3.28.
Murrell S A F.1976.Rheology of Lithosphere:Experimental Indications[J].Tectonophysics,36:5—24.
马杏垣主编.1987.中国岩石圈动力学纲要[M].北京:地质出版社.p.66.MA Xing-yuan(ed).1987.Outline of Lithospheric Dynamics in China[M].Geologic Publishing House,Beijing(inChinese).
袁学诚主编.1996.中国地球物理图集[Z].北京:地质出版社.YUAN Xue-cheng(ed).1996.Geophysics Atlas in China[Z].Geologic Publishing House,Beijing(in Chinese).
张培震,徐锡伟,闻学泽,等.2008.2008年汶川8.0级地震发震断裂的滑动速率、复发周期和构造成因[J].地球物理学报,51(4):1066—1073.ZHANG Pei-zhen,XU Xi-wei,WEN Xue-ze,et al.2008.Slip rates and recurrence intervals of the Longmenshan activefault zone,and tectonic implication for the mechanism of the May12Wenchuan earthquake,2008,Sichuan,China[J].Chinese Journal of Geophsics,51(4):1066—1073(in Chinese).
Allen T.PAGER-CAT[DB/OL].http:∥earthquake.usgs.gov/research/data/pager/.2008.3.28.
Murrell S A F.1976.Rheology of Lithosphere:Experimental Indications[J].Tectonophysics,36:5—24.
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