Department of Earth Sciences, University of Southern California, Los Angeles, California 90089-0740, USA.
Department of Geology, Utah State University, Logan, Utah 84322-4505, USA.
Nature. 2015 Aug 27;524(7566):458-61. doi: 10.1038/nature14867.
Understanding the causes of intraplate earthquakes is challenging, as it requires extending plate tectonic theory to the dynamics of continental deformation. Seismicity in the western United States away from the plate boundary is clustered along a meandering, north-south trending 'intermountain' belt. This zone coincides with a transition from thin, actively deforming to thicker, less tectonically active crust and lithosphere. Although such structural gradients have been invoked to explain seismicity localization, the underlying cause of seismicity remains unclear. Here we show results from improved mantle flow models that reveal a relationship between seismicity and the rate change of 'dynamic topography' (that is, vertical normal stress from mantle flow). The associated predictive skill is greater than that of any of the other forcings we examined. We suggest that active mantle flow is a major contributor to seismogenic intraplate deformation, while gravitational potential energy variations have a minor role. Seismicity localization should occur where convective changes in vertical normal stress are modulated by lithospheric strength heterogeneities. Our results on deformation processes appear consistent with findings from other mobile belts, and imply that mantle flow plays a significant and quantifiable part in shaping topography, tectonics, and seismic hazard within intraplate settings.
理解板内地震的成因具有挑战性，因为这需要将板块构造理论扩展到大陆变形的动力学研究中。远离板块边界的美国西部的地震活动集中在一条蜿蜒的、南北走向的“山间”地带。该带与从薄的、活跃变形到更厚的、构造活动较弱的地壳和岩石圈的转变相吻合。尽管这种结构梯度被用来解释地震活动的定位，但地震活动的根本原因仍不清楚。在这里，我们展示了改进的地幔流模型的结果，该模型揭示了地震活动与“动态地形”（即地幔流产生的垂直法向应力）速率变化之间的关系。相关的预测能力优于我们研究的任何其他力。我们认为，活跃的地幔流是引发板内地震变形的主要因素，而重力位能变化的作用较小。地震活动的定位应发生在垂直法向应力的对流变化被岩石圈强度非均质性调制的地方。我们关于变形过程的结果似乎与其他活动带的研究结果一致，并表明地幔流在塑造板内环境中的地形、构造和地震危险方面起着重要和可量化的作用。
