应力扰动对地震周期和地震矩影响的数值模拟
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摘要
利用二维有限元数值模型,结合断层滑移弱化摩擦准则对断层滑动规律以及应力扰动对其影响进行了研究.数值计算结果表明,在均匀应力分布情况下,平面断层滑动显示出典型的特征地震规律,断层面上的应力扰动对断层滑动规律产生影响,压应力增加明显延迟地震的发生时间,并增加地震释放的能量.应力扰动发生在地震破裂临界区时的影响比在震前滑移区时的影响显著.当发生在地震滑移区时,若应力扰动足够大,则压应力增大会造成地震发生时部分动力断层被暂时锁住,使得地震释放的能量变小,但可增加后续地震的能量;而压应力减小则可导致地震规律产生更加复杂的变化,会即时触发地震.如果应力扰动发生在一个地震周期的早期,则触发的地震较小,但可导致随后的地震提前发生;如果应力扰动发生在一个地震周期的后期,则会触发大地震.当应力扰动位于震前滑移区或破裂临界区时,小的扰动也可能产生类似的效果.应力扰动产生越晚,这种影响也越明显.应力扰动发生在破裂临界区的影响最明显.应力扰动的影响一般主要集中在应力发生扰动后的1—2个地震周期内.后续地震基本恢复无应力扰动时的特征地震规律.
The influences of stress disturbance on earthquake cycle were studied based on a 2D finite element model by employing a dynamic fault with slipweakening friction law.Numerical results show that the stick-slip process of the dynamic fault in a model with uniform background stress behaves like typical characteristic earthquakes,which could be influenced by stress disturbance on the fault.Increasing pressure or decreasing normal stress on the fault delays the occurrence of the following earthquake and enlarges its size,which is more prominent if the stress disturbance locates on the critical rupture zone than on pre-seismic slip zone.If the increased pressure locates on the earthquake slip zone and is large enough,part of the dynamic fault could be locked temporally,thus decreasing the following earthquake size,but enlarging the next earthquake.The influence of decreasing pressure on the fault is more complicate than increasing pressure.If the decreased pressure is large enough,an earthquake could be triggered immediately.If the pressure is decreased at earlier stage of an earthquake cycle,the triggered earthquake usually is a small one,and the next earthquake happens at a shorter time than the time interval of the characteristic earthquakes;on contrary,if the pressure is decreased at later stage of an earthquake cycle,a large earthquake will be triggered immediately.If the stress disturbance locates on pre-seismic slip zone or critical rupture zone,a smaller stress disturbance could produce a similar result;and the later disturbance happens,the more prominent the influence is.The influences are the most prominent when disturbance locates on critical rupture zone.It should be pointed out that the influences of stress disturbance are usually confined within one or two earthquake cycles,and the following earthquake cycles are nearly identical with those without stress disturbance.
引文
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