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首页> 外文期刊>Geological Society of America Bulletin >Size-dependent comminution, tectonic mixing, and sealing behavior of a 'structurally oversimplified' fault zone in poorly lithified sands: Evidence for a coseismic rupture?
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Size-dependent comminution, tectonic mixing, and sealing behavior of a 'structurally oversimplified' fault zone in poorly lithified sands: Evidence for a coseismic rupture?

机译：弱化砂岩中“结构上过于简单化”的断层带的尺寸依赖性粉碎，构造混合和封闭性：同震破裂的证据吗？

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摘要

We studied a structurally oversimplified, extensional fault zone developed in poorly lithified, quartz-rich, high-porosity sandy sediments of the seismically active Crotone Basin (southern Italy). The fault zone consists of a cm-thick, discrete fault core embedded in virtually undeformed wall sediments. By combining grain size, shape, and microstructural analyses with mineralogical analyses and permeability measurements, we investigated the influence of initial sedi-mentological characteristics of sands on the final faulted granular products and related hydrologic properties. Faulting produces a general grain-size and porosity reduction by changing both the grain-size and shape distributions. We document a combination of intragranular fracturing, spalling, and flaking of grain edges in the fault core, which do not depend on grain mineralogy. The dominance of cataclasis, also confirmed by fractal dimensions >2.6, is generally not expected at a deformation depth <1 km. Initial grain size exerts a fundamental control on the comminution process and on the resulting permeability variations up to four orders of magnitude. Coarse-grained sand shows a much higher comminution intensity, grain-shape variations, and permeability drop than finegrained sands. This is because coarser aggregates have (1) fewer grain-to-grain contacts for a given area, which results in higher stress concentration at contact points, and (2) a higher probability of preexisting, intragranular microstructural defects that result in a lower grain strength. The peculiar structural architecture, the dominance of cataclasis over nondestructive particulate flow, and the compositional variations of clay minerals in the fault core strongly suggest that the studied fault zone developed by a coseismic rupture.
机译：我们研究了地震活跃的克罗托尼盆地（意大利南部）的石化较差，富含石英的高孔隙度砂质沉积物中发育的结构过于简单的伸展断裂带。断层带由几厘米厚的离散断层岩心组成，嵌在几乎未变形的壁沉积物中。通过将粒度，形状和微观结构分析与矿物学分析和渗透率测量相结合，我们研究了砂的初始沉积学特征对最终断层颗粒产品和相关水文性质的影响。通过改变晶粒尺寸和形状分布，断层可产生一般的晶粒尺寸和孔隙率降低。我们记录了断层核心中颗粒边缘的颗粒内破裂，剥落和剥落的组合，这与颗粒矿物学无关。分形维数大于2.6的结果也证实了催化作用的优势，通常在变形深度小于1 km的情况下。初始晶粒大小对粉碎过程和最终的磁导率变化（最多四个数量级）施加基本控制。与细粒砂相比，粗粒砂显示出更高的粉碎强度，颗粒形状变化和渗透率下降。这是因为较粗的聚集体在给定的区域中具有（1）较少的晶粒间接触，这导致接触点处的应力集中较高;（2）预先存在的晶粒内微结构缺陷的可能性较高，从而导致较低的晶粒强度。奇特的构造构造，非破坏性颗粒流的催化作用优势以及断层岩心中粘土矿物的成分变化，强烈表明，该地震断层是由同震破裂形成的。

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