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Frictional and structural controls of seismic super-cycles at the Japan trench
Earth, Planets and Space ( IF 3.362 ) Pub Date : 2020-05-11 , DOI: 10.1186/s40623-020-01185-3
Sylvain Barbot

The diverse mechanical behaviors of subduction zones during the seismic cycle emerge from the nonlinear dynamics of a complex mechanical system with interacting brittle and ductile deformation. The 2011 Tohoku mega-quake represents the culmination of a super-cycle of partial and full ruptures of the plate interface, but the physical controls on the down-dip segmentation of the megathrust remain unclear. Here, we propose a two-dimensional rheological model of the Japan trench to explain the variability of earthquake size at the Miyagi section, in northern Honshu, during the last century. We simulate seismicity in a continuum with a physics-based rate- and state-dependent constitutive law for fault slip, producing aperiodic earthquake sequences with a power-law distribution of rupture sizes. Although some partial ruptures of the megathrust are the result of self-emergent behavior, others are structurally controlled. The 1978 and 2005 Mj $$\sim$$ ∼ 7 interplate earthquakes took place in a metamorphic belt in the mantle wedge corner bounded up-dip by the arc Moho that constitutes a permanent structural boundary. We explain the succession of the great 1981 Mw = 7.1 and 2003 Mw = 6.9 earthquakes within the forearc and the 2011 giant earthquake as the natural response of a large continuously velocity-weakening fault with a small nucleation size. The shallow segment below the frontal prism only slips in giant through-going ruptures that unzip the whole velocity-weakening interface. The model consistently explains the size, recurrence time, and hypocenter location of historical earthquakes in the Miyagi segment, the slow-slip and foreshock preparatory phase of the 2011 Tohoku earthquake, the large slip near the trench during the giant rupture, and important features of its postseismic deformation. The complex patterns of seismicity at the Japan trench can be better understood by assimilating geological and geophysical observations at various periods of the seismic cycle within an explicative physical framework.

中文翻译:

日本海沟地震超级周期的摩擦和结构控制

地震周期中俯冲带的不同力学行为源于复杂机械系统的非线性动力学,具有相互作用的脆性和延性变形。2011 年的东北大地震代表了板块界面部分和完全破裂的超级周期的高潮,但对巨型逆冲断层下倾分段的物理控制仍不清楚。在这里,我们提出了日本海沟的二维流变模型,以解释上个世纪本州北部宫城地区地震规模的变化。我们使用基于物理的速率和状态相关的断层滑动本构律模拟连续体中的地震活动,产生具有破裂尺寸幂律分布的非周期性地震序列。虽然大推力的一些部分破裂是自发行为的结果,但其他部分则受到结构控制。1978 年和 2005 年 Mj $$ \ sim $$ ∼ 7 次板间地震发生在地幔楔角的变质带中,由构成永久结构边界的弧莫霍面向上倾斜。我们将 1981 年 Mw = 7.1 和 2003 年 Mw = 6.9 大地震和 2011 年大地震的连续性解释为具有小成核尺寸的大型连续速度减弱断层的自然响应。前棱柱下方的浅段仅在巨大的贯穿断裂中滑动,从而解开整个速度减弱界面。该模型一致地解释了宫城段历史地震的大小、复发时间和震源位置,2011 年东北地震的慢滑移和前震准备阶段,巨大破裂期间海沟附近的大滑移,以及其震后变形的重要特征。通过在解释性物理框架内同化地震周期不同时期的地质和地球物理观测,可以更好地了解日本海沟的复杂地震活动模式。
更新日期:2020-05-11
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