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Mapping the fracture network in the Lilstock pavement, Bristol Channel, UK: manual versus automatic
Solid Earth ( IF 3.2 ) Pub Date : 2020-09-18 , DOI: 10.5194/se-11-1773-2020
Christopher Weismüller , Rahul Prabhakaran , Martijn Passchier , Janos L. Urai , Giovanni Bertotti , Klaus Reicherter

The 100 000 m2 wave-cut pavement in the Bristol Channel near Lilstock, UK, is a world-class outcrop, perfectly exposing a very large fracture network in several thin limestone layers. We present an analysis based on manual interpretation of fracture generations in selected domains and compare it with automated fracture tracing. Our dataset of high-resolution aerial photographs of the complete outcrop was acquired by an unmanned aerial vehicle, using a survey altitude optimized to resolve all fractures. We map fractures and identify fracture generations based on abutting and overprinting criteria, and we present the fracture networks of five selected representative domains. Each domain is also mapped automatically using ridge detection based on the complex shearlet transform method. The automatic fracture detection technique provides results close to the manually traced fracture networks in shorter time but with a bias towards closely spaced Y over X nodes. The assignment of fractures into generations cannot yet be done automatically, because the fracture traces extracted by the automatic method are segmented at the nodes, unlike the manual interpretation in which fractures are traced as a path from fracture tip to fracture tip and consist of several connected segments. This segmentation makes an interpretation of relative age impossible, because the identification of correct abutting relationships requires the investigation of the complete fracture trace by following a clearly defined set of rules. Generations 1 and 2 are long fractures that traverse all domains. Generation 3 is only present in the southwestern domains. Generation 4 follows an ENE–WSW striking trend, is suborthogonal to generations 1 and 2, and abuts on them and generation 3, if present. Generations 5 is the youngest fracture set with a range of orientations, creating polygonal patterns by abutting at all other fracture generations. Our mapping results show that the northeastern domains only contain four fracture generations; thus, the five generations of the outcrop identified in the southwestern domains are either not all present in each of the five domains or vary locally in their geometry, preventing the interpreter from linking the fractures to their respective generation over several spatially separate mapping domains. Fracture intensities differ between domains where the lowest is in the NE with 7.3 m−1 and the highest is in the SW with 10 m−1, coinciding with different fracture orientations and distributions of abutting relationships. Each domain has slightly different fracture network characteristics, and greater connectivity occurs where the development of later shorter fractures is not affected by the stress shadowing of pre-existing longer fractures.

中文翻译:

在英国布里斯托尔海峡的Lilstock路面中绘制裂缝网络图:手动与自动

100000 m 2英国利斯托克(Lilstock)附近的布里斯托尔海峡(Bristol Channel)的波切路面是世界级的露头,完全暴露了由几个薄石灰岩层组成的非常大的裂缝网络。我们提出基于对选定域中裂缝生成的人工解释的分析,并将其与自动裂缝追踪进行比较。我们的完整露头高分辨率航拍照片数据集是由无人驾驶飞机使用的,其测量高度经优化可解决所有裂缝。我们绘制了裂缝图,并根据邻接和套印标准确定了裂缝的产生,并提出了五个选定代表性区域的裂缝网络。每个域也将根据复杂的Sletlet变换方法使用岭检测自动映射。自动裂缝检测技术可在更短的时间内提供接近于手动跟踪的裂缝网络的结果,但偏向于X节点上的Y间距很小。裂缝的划分还不能自动完成,因为通过自动方法提取的裂缝痕迹在节点处被分割,这与手动解释不同,在人工解释中,裂缝被追踪为从裂缝尖端到裂缝尖端的路径,并且由多个相连的裂缝组成段。这种分割使得无法解释相对年龄,因为要确定正确的邻接关系,需要遵循一组明确定义的规则来研究完整的骨折痕迹。第1代和第2代是遍及所有区域的长裂缝。第三代仅存在于西南地区。第4代遵循ENE–WSW的惊人趋势,与第1代和第2代正交,并紧靠它们和第3代(如果存在)。第5代裂缝是一系列方向最年轻的裂缝,通过与所有其他裂缝世代邻接形成多角形图案。我们的测绘结果表明,东北地区仅包含四个裂缝世代;而第二个裂缝世代中只有四个。因此,在西南地区识别出的露头的第5代不是全部存在于这5个领域中,还是在几何形状上局部变化,从而阻止了解释者将裂缝与其在多个空间上分开的制图领域中的相应年代联系起来。最低强度在7.3 m的NE中的区域之间的断裂强度不同 并紧靠它们,如果有的话,紧靠第三代。第5代裂缝是一系列方向最年轻的裂缝,通过与所有其他裂缝世代邻接形成多角形图案。我们的测绘结果表明,东北地区仅包含四个裂缝世代;而第二个裂缝世代中只有四个。因此,在西南地区识别出的露头的第5代不是全部存在于这5个领域中,还是在几何形状上局部变化,从而阻止了解释者将裂缝与其在多个空间上分开的制图领域中的相应年代联系起来。最低强度在7.3 m的NE中的区域之间的断裂强度不同 并紧靠它们,如果有的话,紧靠第3代。第5代裂缝是一系列方向最年轻的裂缝,通过与所有其他裂缝世代邻接形成多角形图案。我们的测绘结果表明,东北地区仅包含四个裂缝世代;而第二个裂缝世代中只有四个。因此,在西南地区识别出的露头的第5代不是全部存在于这5个领域中,还是在几何形状上局部变化,从而阻止了解释者将裂缝与其在多个空间上分开的制图领域中的相应年代联系起来。最低强度在7.3 m的NE中的区域之间的断裂强度不同 通过邻接所有其他裂缝世代来创建多边形图案。我们的测绘结果表明,东北地区仅包含四个裂缝世代;而第二个裂缝世代中只有四个。因此,在西南地区识别出的露头的第5代不是全部存在于这5个领域中,还是在几何形状上局部变化,从而阻止了解释者将裂缝与其在多个空间上分开的制图领域中的相应年代联系起来。最低强度在7.3 m的NE中的区域之间的断裂强度不同 通过邻接所有其他裂缝世代来创建多边形图案。我们的测绘结果表明,东北地区仅包含四个裂缝世代;而第二个裂缝世代仅占四个。因此,在西南地区识别出的露头的第5代不是全部存在于这5个领域中,还是在几何形状上局部变化,从而阻止了解释者将裂缝与其在多个空间上分开的制图领域中的相应年代联系起来。最低强度在7.3 m的NE中的区域之间的断裂强度不同 防止解释器在多个空间上分开的映射域上将骨折与它们各自的世代联系起来。最低强度在7.3 m的NE中的区域之间的断裂强度不同 防止解释器将骨折与其在多个空间上分开的映射域中的相应裂缝链接起来。最低强度在7.3 m的NE中的区域之间的断裂强度不同-1且最高的是西南部的10 m -1,这与不同的裂缝方向和邻接关系的分布相吻合。每个区域的裂缝网络特征稍有不同,并且在以后较短的裂缝的发展不受先前存在的较长裂缝的应力遮蔽影响的地方,会出现更大的连通性。
更新日期:2020-09-20
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