中科大地球与行星物理学术报告通知-Jens-Erik Lundstern (Lund Snee)

The stress field controls active deformation of the Earth’s crust and reflects the processes that drive plate tectonics. In this talk, I present the recently published next-generation stress map of North America, which includes hundreds of new orientations of the maximum horizontal stress (S_Hmax) as well as the continent’s first quantitative map of relative stress magnitudes (faulting regime). The new dataset shows that the stress field varies over a range of spatial scales. In the compressive eastern parts of the continent, S_Hmax orientations vary gradually over large distances, suggesting that they are mainly influenced by plate-scale forces such as tractions at the base of the lithosphere and compression imposed by the geoid high along the Mid-Atlantic Ridge. However, rotations up to 90° over tens of kilometers are apparent in the extensional, tectonically active western U.S. These short-wavelength S_Hmax rotations suggest shallow sources of stress and may be analogous to rotations observed along the margins of the Sichuan Basin, China. As I show, multiscale stress variability poses challenges for geodynamic models attempting to determine the sources of crustal stress. Finally, in addition to their utility for subsurface energy development, I demonstrate how the maps can be used to identify which mapped faults may be most sensitive to induced seismicity associated with energy development or subsurface fluid storage. I conclude by presenting learnings from recent induced seismicity in the U.S. that has been linked principally with deep wastewater disposal, with a lesser proportion linked to hydraulic fracturing and geothermal operations.

地壳的活动变形受应力场控制，并反映了驱动板块构造的过程。本次报告将介绍最近发表的北美下一代地应力地图，其中包括数百个新的最大水平应力（SHmax）方向数据，并首次展现定量的相对应力大小（断层形成机制）。新的应力数据集显示应力场在不同空间尺度上的变化。在北美大陆东部（以挤压为主），SHmax 的方向在较大距离上逐渐变化，这表明它们主要受到诸如岩石圈底部的牵引力和大西洋中脊沿线的重力高压迫等板块尺度力量的影响。然而，在北美大陆西部（以拉伸为主），SHmax 的方向在数十公里范围内呈现了高达90°的旋转。这些短波长的SHmax 旋转表明应力的浅层来源，并可能类似于在中国四川盆地边缘某些地区观察到的应力旋转现象。正如所展示的，多尺度的应力不均质性对试图确定地壳应力来源的地球动力学模型提出了挑战。地应力地图可以应用于地下资源的开发，还可以确定哪些已探明的断层可能在人工扰动情况下诱发地震。本报告还将总结最近美国发生的与深层废水回灌相关的诱发地震案例，并指出其中较小比例与水力压裂和地热开发存在关联性。