【摘要】 分析了华北地区自1976年以来MS≥6.0地震前地下流体长趋势变化的形态、演化特征。结果表明:地下流体长趋势变化出现时间早、范围广,具有协调性、重复性、迁移性等特性,主要沿构造带迁移,迁移方向为外围向内迁移或内部向外迁移;形态主要为趋势转折、破年变、加速等,其中绝对大多数为趋势转折变化;地下水位分析表明长趋势变化绝大部分呈现为缓慢上升或下降减缓的走势。对比研究了地壳形变与地下流体长趋势变化,发现地壳形变长趋势时间早于地下流体;形变出现张压变化与水位变化有比较密切的关系,即形变绝大部分出现缓慢压性变化或张性减缓变化,水位绝大部分出现缓慢上升或下降减缓变化。最后讨论了强震前地下流体长趋势变化产生的机理:在地震孕育过程初(早)期,构造应力的缓慢增强将使岩体所含裂缝闭合,地壳发生变形,从而改变岩体的空隙率及相应的孔隙压力和渗透率,引起诸如地下流体长趋势动态异常变化;构造应力缓慢增强并向未来震中聚集,造成地下流体长趋势动态异常变化向震中迁移;而深部物质的不断上涌和影响范围增大致使地下流体长趋势动态异常变化向外围迁移。更多还原

【Abstract】 The long-time trend change shape and evolutionary characteristics of subsurface fluid in North China before MS≥6.0 earthquakes since 1976 are analysed.The results show that the begin time of long-time trend change of subsurface fluid is earlier,and the range is wider,with the characteristics of compatibility,repetition and migration etc.The migrate direction along major tectonic belt is from wide outer regions to epicenter area,or from epicenter area to wide outer region.The shape of changes show trend turn change,damage annual variation and accelerating variation etc,among them the trend turn change is majority shape.Study on level of underground water shows that the majority variation shapes of long-time trend change on level of underground water are slow elevation or descending diminution.Then long-time trend change of subsurface fluid and crustal deformation before strong earthquakes are comparatively studied.The results discover that the begin time of crustal deformation is earlier than it of subsurface fluid,the tensor-pressure variation of crustal deformation is more closely related with the level variation of underground water,namely if change of crustal deformation shows mostly slow pressure or tensor diminution,the change of underground water level shows slow elevation or descending diminution.Finally,the mechanism on long-time trend change of subsurface fluid before strong earthquake is discussed.Slow incremental tectonic stress make crack of rock closure and crust deform,the crust deformation changes porosity,pore pressure and permeability,causes the long-time trend abnormal change of subsurface fluid in the early stage of preparation earthquake.The tectonic stress slowly enhancing and congregating to future seismic center cause the change to migrate into future seismic center.The continuously upwelling of deep material and increment influencing range make the change migrate from future seismic center to outlying zone.更多还原