On December 7, 2012, an earthquake occurred within the Pacific Plate near the Japan Trench, which was composed of deep reverse- and shallow normal-faulting subevents (Mw 7.2 and 7.1, respectively) with a time interval of ~10 s. It had been known that the stress state within the plate was characterized by shallow tensile and deep horizontal compressional stresses due to the bending of the plate (bending stress). This study estimates the fault model of the doublet earthquake utilizing tsunami, teleseismic, and aftershock data and discusses the stress state within the incoming plate and spatiotemporal changes seen in it after the 2011 Tohoku-Oki earthquake. We obtained the vertical extents of the fault planes of deep and shallow subevents as ~45–70 km and ~5 (the seafloor)–35 km, respectively. The down-dip edge of the shallow normal-faulting seismic zone (~30–35 km) deepened significantly compared to what it was in 2007 (~25 km). However, a quantitative comparison of the brittle strength and bending stress suggested that the change in stress after the Tohoku-Oki earthquake was too small to deepen the down-dip end of the seismicity by ~10 km. To explain the seismicity that occurred at a depth of ~30–35 km, the frictional coefficient in the normal-faulting depth range required would have had to be ~0.07 ≤ μ ≤ ~0.2, which is significantly smaller than the typical friction coefficient. This suggests the infiltration of pore fluid along the bending faults, down to ~30–35 km. It is considered that the plate had already yielded to a depth of ~35 km before 2011 and that the seismicity of the area was reactivated by the increase in stress from the Tohoku-Oki earthquake.

中文翻译：

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基于近场海啸的2011年东北大地震上倾角附近的2012年双重地震的断层模型：对板内应力状态的影响

2012年12月7日，在日本海沟附近的太平洋板块内发生了一次地震，该地震由深反向和浅正断层次事件（分别为Mw 7.2和7.1）组成，时间间隔约为10 s。已知由于板的弯曲（弯曲应力），板内的应力状态的特征在于浅的拉伸应力和深的水平压缩应力。这项研究利用海啸，远程地震和余震数据估算了双重地震的断层模型，并讨论了2011年东北冲积地震后传入板块内的应力状态和时空变化。我们获得了深和浅子事件断层平面的垂直范围，分别为〜45-70 km和〜5（海底）-35 km。与2007年（〜25 km）相比，浅层正常断裂地震带（〜30–35 km）的下倾角明显加深。然而，对脆性强度和弯曲应力的定量比较表明，东北大地震后的应力变化太小，不足以使地震活动的下倾端加深约10 km。为了解释在〜30–35 km深度处发生的地震活动，在正常断层深度范围内所需的摩擦系数必须为〜0.07≤μ≤〜0.2，大大小于典型的摩擦系数。这表明沿弯曲断层的孔隙流体渗透率低至约30-35 km。据认为，该板块在2011年之前已经屈服了约35 km的深度，并且该地区的地震活动由于东北冲积地震的应力增加而重新激活。