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Interplate Earthquake Fault Slip During Periodic Earthquake Cycles in a Viscoelastic Medium at a Subduction Zone

机译:俯冲带粘弹性介质中周期性地震周期内的板间地震断层滑动

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A 2-D finite-element-method (FEM) numerical experiment of earthquake cycles at a subduction zone is performed to investigate the effect of viscoelasticity of the earth on great interplate earthquake fault slip. We construct a 2-D viscoelastic FEM model of northeast Japan, which consists of an elastic upper crust and a viscoelastic mantle wedge under gravitation overlying the subducting elastic Pacific plate. Instead of the dislocation model prescribing an amount of slip on a plate interface, we define an earthquake cycle, in which the plate interface down to a depth is locked during an interseismic period and unlocked during coseismic and postseismic periods by changing the friction of the boundary with the master-slave method. This earthquake cycle with steady plate subduction is periodically repeated to calculate the resultant earthquake fault slip. As simulated in a previous study (Wang, 1995), the amount of fault slip at the first earthquake cycle is smaller than the total relative plate motion. This small amount of fault slip in the viscoelastic medium was considered to be one factor explaining the small seismic coupling observed at several subduction zones. Our simulation, however, shows that the fault slip grows with an increasing number of repeated earthquake cycles and reaches an amount comparable to the total relative plate motion after more than ten earthquake cycles. This new finding indicates that the viscoelasticity of the earth is not the main factor in explaining the observed small seismic coupling. In comparison with a simple one-degree-of-freedom experiment, we demonstrate that the increase of the fault slip occurs in the transient state from the relaxed initial state to the stressed equilibrium state due to the intermittent plate loading in a viscoelastic medium.
机译:进行了俯冲带地震周期的二维有限元方法(FEM)数值试验,以研究地球的粘弹性对板间大地震断层滑动的影响。我们构建了日本东北部的二维粘弹性有限元模型,该模型由弹性上地壳和重力作用下的俯冲弹性太平洋板块上的粘弹性地幔楔组成。我们没有使用错位模型规定板块界面上的滑动量,而是定义了一个地震周期,在该地震周期中,通过改变边界的摩擦,板块界面的深度在地震期间被锁定,而在同震和后地震期间被解锁。使用主从方法。周期性重复这种具有稳定板块俯冲的地震周期,以计算最终的地震断层滑动。如先前的研究(Wang,1995)所模拟的那样,第一个地震周期的断层滑动量小于总的相对板块运动。粘弹性介质中的少量断层滑动被认为是解释在几个俯冲带观察到的小地震耦合的一个因素。然而,我们的模拟表明,断层滑动随着重复的地震循环次数的增加而增长,并且在十次以上的地震循环后达到与总相对板块运动相当的程度。这一新发现表明,地球的粘弹性不是解释观测到的小地震耦合的主要因素。与简单的单自由度实验相比,我们证明了断层滑移的增加是由于粘弹性介质中板的间歇性加载而在从松弛初始状态到应力平衡状态的过渡状态中发生的。

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