United States Geological Survey, Geologic Hazards Science Center, P.O. Box 25046, DFC MS966, Denver, Colorado 80225, USA.
Fugro Consultants Inc. 1726 Cole Boulevard, Suite 230, Lakewood, Colorado 80401, USA.
Nat Commun. 2017 Feb 17;8:14314. doi: 10.1038/ncomms14314.
Earthquakes far from tectonic plate boundaries generally exploit ancient faults, but not all intraplate faults are equally active. The North American Great Plains exemplify such intraplate earthquake localization, with both natural and induced seismicity generally clustered in discrete zones. Here we use seismic velocity, gravity and topography to generate a 3D lithospheric density model of the region; subsequent finite-element modelling shows that seismicity focuses in regions of high-gravity-derived deviatoric stress. Furthermore, predicted principal stress directions generally align with those observed independently in earthquake moment tensors and borehole breakouts. Body forces therefore appear to control the state of stress and thus the location and style of intraplate earthquakes in the central United States with no influence from mantle convection or crustal weakness necessary. These results show that mapping where gravitational body forces encourage seismicity is crucial to understanding and appraising intraplate seismic hazard.
远离构造板块边界的地震通常利用古老的断层，但并非所有板块内断层的活动性都相同。北美大平原就是这种板块内地震定位的一个例子，无论是天然地震还是诱发地震通常都集中在离散的区域。在这里，我们利用地震波速度、重力和地形来生成该地区的三维岩石圈密度模型；随后的有限元模拟表明，地震活动集中在高重力衍生的偏应力区域。此外，预测的主应力方向通常与在地震矩张量和井眼破裂中独立观测到的方向一致。因此，重力体的作用力似乎控制着应力状态，从而控制了美国中部的板块内地震的位置和类型，而不需要地幔对流或地壳软弱的影响。这些结果表明，绘制出重力体的作用力鼓励地震发生的区域对于理解和评估板块内地震的危险性至关重要。
