孕震介质水动力学性质对前兆场影响的研究
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摘要
提出了纵向非均匀、饱含液体多孔介质孕震动力学方程组的数值解法。为了考虑非弹性效应 ,对该方程组采用增量形式求解。提供了当存在垂直力源和纵向非均匀时 ,定量分析研究垂直剖面上的地震孕育过程及其前兆变化机制的方法和软件。选用了一个饱含液体的双层地壳模型 ,运用所研制的软件计算分析了介质孔隙度、渗透率等地壳水动力学性质对前兆场的影响。研究发现 ,孕震介质孔隙度的大小对前兆场的分布可以产生显著影响。孔隙度较大时 ,非弹性体积膨胀 (前兆 )的出现和变化一开始仅局限于断层附近区域 ,同时非弹性膨胀 (前兆 )持续的时间 (前兆持时 )占总孕震时间的比率较大 ;孔隙度较小时 ,非弹性体积膨胀除在紧靠断层的区域内孕震早期会出现非弹性膨胀 (前兆 )外 ,在离断层较远的区域内早期也会出现前兆异常。介质渗透率对前兆场的影响主要表现在 :当其它条件完全相同 ,仅介质渗透率不同时 ,较低的渗透率会推迟前兆异常的发生 ,同时使前兆异常首先在断层附近出现 ,然后向外扩展 ,并且使孕震过程变长 ;而当渗透率较高时 ,前兆异常一开始便会展布在断层周围及其远离断层的较大范围内
The numerical method was advanced for solving seismogenic dynamic coupled equation of longitudinally-heterogeneous,water-saturated,porous medium.Considering inelastic effect,the coupled equation was solved by using increment.The method and soft of quantitatively analyzing and studying earthquake-generating process and its precursory variation mechanism in vertical section were given.A water-saturated double-layered crustal method was selected.The compiled soft was used to analyze the effect of crustal hydrodynamic properties such as medium porosity,permeability,etc., on precursor field.It is found through research that the porosity of seismogenic medium effects the distribution of precursor field obviously.When the porosity is large,inelastic volumetric dilation (precursor) will occur and change in the area near the fault in the beginning,and the duration of the inelastic dilation(duration of precursor)takes much time of total seismogenic process;when the porosity is small,inelastic volumetric dilation will appear not only in the area near the fault but also the area far away the fault in the beginning.The effect of medium permeability on precursor field is shown as:when other conditions is the same but medium permeability,lower permeability will defer precursory anomaly occurring and make anomaly appear at first near the fault then extend outside,but higher permeability will make precursory anomaly widely appear around the fault and in a large area far away the fault at the first beginning.
The numerical method was advanced for solving seismogenic dynamic coupled equation of longitudinally-heterogeneous,water-saturated,porous medium.Considering inelastic effect,the coupled equation was solved by using increment.The method and soft of quantitatively analyzing and studying earthquake-generating process and its precursory variation mechanism in vertical section were given.A water-saturated double-layered crustal method was selected.The compiled soft was used to analyze the effect of crustal hydrodynamic properties such as medium porosity,permeability,etc., on precursor field.It is found through research that the porosity of seismogenic medium effects the distribution of precursor field obviously.When the porosity is large,inelastic volumetric dilation (precursor) will occur and change in the area near the fault in the beginning,and the duration of the inelastic dilation(duration of precursor)takes much time of total seismogenic process;when the porosity is small,inelastic volumetric dilation will appear not only in the area near the fault but also the area far away the fault in the beginning.The effect of medium permeability on precursor field is shown as:when other conditions is the same but medium permeability,lower permeability will defer precursory anomaly occurring and make anomaly appear at first near the fault then extend outside,but higher permeability will make precursory anomaly widely appear around the fault and in a large area far away the fault at the first beginning.
引文
[1]牛志仁,陈觉民,李炳乾.唐山大地震孕育过程的数值模拟研究[J].地震学报,1997,19(4):347～358.
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[4]梅世蓉.地震科学研究论文选集[C].北京:地震出版社,1993.
[2]中国地震局预测预防司.大陆地震预报的方法和理论[M].北京:地震出版社,1998.
[3]赵和云,梁子彬,李炳乾等.青海省共和7.0级地震前兆的数值模拟[J].地震学报,1997,19(4):359～366.
[4]梅世蓉.地震科学研究论文选集[C].北京:地震出版社,1993.
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