Active normal faulting during the 1997 seismic sequence in Colfiorito, Umbria: Did slip propagate to the surface?
Active normal faulting during the 1997 seismic sequence in Colfiorito, Umbria: Did slip propagate to the surface?
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DOI：
10.1016/j.jsg.2016.08.011
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发表时间：
2016-10-01
影响因子：
3.1
通讯作者：
McCaffrey, Ken J. W.
中科院分区：
文献类型：
--
作者：
Mildon, Zoe K.;Roberts, Gerald P.;McCaffrey, Ken J. W.
为了确定1997年9月26日地震期间的滑动是否传播到地表，收集了意大利翁布里亚基岩断层陡坡沿线的构造数据。这些收集的数据被用来研究与有争议的地表破裂(在基岩断层陡坡底部观察到的苍白的未风化条带)相关的抛撒与走向、倾角和滑动矢量之间的关系。前人的研究表明，地表破裂要么是由原生地表滑动产生的，要么是由于上盘沉积物的二次压实作用而产生的。一些作者倾向于后者，因为稀疏的地表断层倾角测量与深度的节面倾角不匹配。文中论证了地表破裂的走向、倾角和高度与基岩断层的几何学和运动学之间存在着系统的关系。走向和倾角是不同的，当走向与记录最高倾斜值的滑动向量方位角倾斜时，投掷最大。这意味着，投掷值的变化是为了适应断层在断层面波纹上走向和倾角的空间变化，这一特征是通过描述断层应变守恒的理论预测的，而不是通过压实作用预测的。此外，当考虑到地表倾角的自然变化和深部节面倾角的不确定性时，公布的地震位置和报告的断层倾角与分析的地表陡峭一致。这意味着新的条带确实是原生的同震地表破裂，其滑动与深部的发震断层有关。我们讨论了如何将这种活动断层的位置和几何形状的知识用作地震危险性评估的输入。(C)2016年提交人。爱思唯尔有限公司出版。
In order to determine whether slip during an earthquake on the 26th September 1997 propagated to the surface, structural data have been collected along a bedrock fault scarp in Umbria, Italy. These collected data are used to investigate the relationship between the throw associated with a debated surface rupture (observed as a pale unweathered stripe at the base of the bedrock fault scarp) and the strike, dip and slip-vector. Previous studies have suggested that the surface rupture was produced either by primary surface slip or secondary compaction of hangingwall sediments. Some authors favour the latter because sparse surface fault dip measurements do not match nodal plane dips at depth. It is demonstrated herein that the strike, dip and height of the surface rupture, represented by a pale unweathered stripe at the base of the bedrock scarp, shows a systematic relationship with respect to the geometry and kinematics of faulting in the bedrock. The strike and dip co-vary and the throw is greatest where the strike is oblique to the slip-vector azimuth where the highest dip values are recorded. This implies that the throw values vary to accommodate spatial variation in the strike and dip of the fault across fault plane corrugations, a feature that is predicted by theory describing conservation of strain along faults, but not by compaction. Furthermore, published earthquake locations and reported fault dips are consistent with the analysed surface scarps when natural variation for surface dips and uncertainty for nodal plane dips at depth are taken into account. This implies that the fresh stripe is indeed a primary coseismic surface rupture whose slip is connected to the seismogenic fault at depth. We discuss how this knowledge of the locations and geometry of the active faults can be used as an input for seismic hazard assessment. (C) 2016 The Authors. Published by Elsevier Ltd.