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首页> 外文期刊>Journal of Volcanology and Geothermal Research2012V243-244NOCT,15 >Dike-induced stresses and displacements in layered volcanic zones
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Dike-induced stresses and displacements in layered volcanic zones

机译：层状火山区中堤坝引起的应力和位移

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摘要

During a volcanic unrest period with dike injection, one of the main scientific tasks is to assess the geometry and the propagation path of the dike and, in particular, the likelihood of the dike reaching the surface to erupt Currently, the dike path and geometry (including depth and opening/aperture) are both partly determined from geodetic surface data using mostly dislocation models that assume the volcanic zone/volcano to be an elastic half space of uniform mechanical properties. By contrast, field observations of volcanic zones/volcanoes (active and extinct) show that they are composed of numerous layers whose mechanical properties (primarily Young's modulus) vary widely and whose contacts commonly arrest dikes. Here we provide field observations and numerical models on the effects of a typical variation in Young's modulus in an active volcanic zone on the internal and surface stresses and displacements induced by a dike whose tip is arrested at 0.5 km depth below the surface of the volcanic zone. Above the layer or unit hosting the dike are four layers of equal thickness. We vary the Young's modulus or stiffness of the fourth layer (the one adjacent to the layer or unit hosting the dike) from 10 GPa to 0.01 GPa, while all the other layers/units maintain their Young's moduli in the model runs. The results show that as the fourth layer becomes more compliant or soft (0.1-0.01 GPa) dike-induced stresses and displacements (lateral and vertical) above the layer, including those at the surface, become suppressed but the stresses and displacements of the layer/unit hosting the dike increase and their peaks do not coincide in location or magnitude with those of the other layers. Thus, the dike-induced internal deformation of the volcanic zone increases as the fourth layer becomes softer. Also, the tensile-and-shear stress peaks at the surface occur at locations widely different from those of maximum surface uplift. More specifically, for a comparatively stiff fourth layer (1-10 GPa), the surface tensile and shear stresses peak at lateral distances of 0.5-0.7 km from the projection of the dike to the surface. (Essentially no tensile/shear stresses reach the surface when the fourth layer is as soft as 0.1-0.01 GPa, so that there are no stress peaks). By contrast the maximum surface displacements (uplift) peak at lateral distances of 2.8-3.3 km from the dike projection to the surface. If tension fractures or faults - in particular the boundary faults of a graben - are induced by the dike, they should form at the tensile/shear stress peaks and not, as is commonly suggested, at the location of the surface displacement peaks. Our results thus suggest that any dike-induced graben is likely to be of a width about twice the depth to the tip/top of the arrested dike. The results demonstrate that elastic half-space models overestimate the dike-induced surface stresses, and thus the depth to the tip/top of the associated dike. In particular, the models presented here indicate that, for typical dikes little or no dike-induced surface deformation would be expected until the dike tip propagates to depths below the surface of less than a kilometre. (C) 2019 Elsevier B.V. All rights reserved.
机译：在注入堤坝的火山动荡期间，一项主要的科学任务是评估堤坝的几何形状和传播路径，尤其是评估堤坝到达地面喷发的可能性。目前，堤坝的路径和几何形状（包括深度和开度/孔径）都是使用大部分位错模型从大地表面数据中部分确定的，这些模型假定火山区/火山是具有均匀机械特性的弹性半空间。相比之下，现场对火山区/火山（活动的和灭绝的）的观察表明，它们由许多层组成，这些层的机械性能（主要是杨氏模量）变化很大，并且其接触通常会阻止堤坝。在这里，我们提供了现场观测和数值模型，这些数据和模型涉及活动火山区的杨氏模量的典型变化对堤顶引起的内部应力和表面应力以及位移的影响，堤坝的尖端被截留在火山区表面以下0.5 km的深度。在容纳堤防的层或单元上方是四个相等厚度的层。我们将第四层（与堤防所在的层或单元相邻的层）的杨氏模量或刚度从10 GPa更改为0.01 GPa，而所有其他层/单元在模型运行中保持其杨氏模量。结果表明，随着第四层变得更加柔顺或柔软（0.1-0.01 GPa），堤防引起的应力和层上方（包括表面处的应力）和位移（横向和垂直）被抑制，但是层的应力和位移被抑制堤防增加的/单位，其峰值的位置或大小与其他层的峰值或位置不一致。因此，随着第四层的变软，堤坝引起的火山带内部变形增加。同样，表面的拉伸和剪切应力峰值出现在与最大表面隆起大不相同的位置。更具体地说，对于相对较硬的第四层（1-10 GPa），表面拉伸应力和剪切应力在从堤坝的投影到表面的0.5-0.7 km的横向距离处达到峰值。 （当第四层软至0.1-0.01 GPa时，基本上没有拉伸/剪切应力到达表面，因此没有应力峰值）。相反，最大的表面位移（隆起）在从堤坝投影到地面的横向距离为2.8-3.3 km时达到峰值。如果堤坝引起张性裂缝或断层，特别是a爪的边界断层，则应在拉伸/剪切应力峰值处形成，而不是通常建议在表面位移峰值处形成。因此，我们的结果表明，堤防引起的抓地力的宽度大约是被拦住堤防的尖端/顶部深度的两倍。结果表明，弹性半空间模型高估了堤防引起的表面应力，从而高估了相关堤防尖端/顶部的深度。特别是，这里介绍的模型表明，对于典型的堤防，直到堤防尖端传播到小于一公里的水面以下的深度之前，几乎不会或根本没有堤防引起的表面变形。 （C）2019 Elsevier B.V.保留所有权利。

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