In-situ rock shattering and strain localization along a seismogenic fault in dolostones (Monte Marine fault, Italian Central Apennines)

IF 2.6 2区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY
S. Cortinovis , M. Fondriest , F. Balsamo , A. Lucca , F. La Valle , M. Pizzati , F. Storti , G. Di Toro
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引用次数: 0

Abstract

In-situ shattered rocks are often associated with seismogenic fault zones, but their mechanism of formation is still matter of debate, partly because of the limited number of field studies. Here we describe the characteristics of in-situ shattered rocks distribution along the NW-SE-striking seismogenic Monte Marine Fault (MMF) in the Italian Central Apennines. In the studied area, the MMF cuts through Mesozoic carbonates, is exhumed from <3 km depth and consists of two >5 km-long major hard-linked segments with normal kinematics. The linkage between the two fault segments occurs along a ∼2 km-long step-over zone with E-W trending faults and oblique-slip kinematics. To the northwest, fault-related shear deformation is localized in a ∼5 m-thick cataclastic fault core and off-fault deformation is dominated by in-situ shattered rocks up to ∼40 m-thick. Instead, in the step-over zone to the southeast, the in-situ shattered rocks are up to ∼500 m thick, particularly where MMF crosscuts older low-angle thrust faults.

We integrated detailed field structural surveys with microstructural and grain size distribution analyses of the fault rocks to assess the mechanism of (1) formation of in-situ shattered rocks and, (2) progressive localization of shear deformation along the MMF. The obtained results, after the viability of several formation mechanisms (mechanical models) have been reviewed, support the hypothesis that the formation of in-situ shattered rocks was associated with the propagation of (multiple) seismic ruptures (mainshocks and aftershock sequences) within a mechanically heterogeneous fault zone. Heterogeneity is due to the occurrence of preexisting damage related to previous earthquakes, but also inherited from the older low-angle thrust faults. Therefore, we suggest that the origin of these shattered rocks is more compatible with seismic related processes than only with quasi-static fault growth models. On the other hand, the cataclastic fault core derived from the progressive accommodation of shear deformation within the in-situ shattered rock volumes during several seismic cycles. We conclude that the large volumes of in-situ shattered rocks are the result of seismic-related dissipative processes in a geometrically and mechanically heterogeneous fault zone. In this scenario, large volumes of in-situ shattered rocks are compliant low velocity zones which can influence the propagation of earthquake ruptures.

沿白云岩地震断层的原位岩石破碎和应变定位(意大利亚平宁半岛中部的马林山断层)
原位破碎岩通常与地震断层带有关,但其形成机制仍存在争议,部分原因是实地研究数量有限。在此,我们描述了意大利中部亚平宁山脉西北-东南走向的地震成因蒙特海洋断层(MMF)沿线原位破碎岩分布的特征。在所研究的地区,MMF 穿过中生代碳酸盐岩,从 3 千米深的地方挖掘出来,由两条长达 5 千米、具有正常运动学特征的主要硬连接断层段组成。这两段断层之间的联系发生在一条长达 2 公里的阶梯带,该阶梯带断层呈东西走向,运动方式为斜滑动。在西北方向,与断层有关的剪切变形集中在厚度为 5 米的碎屑岩断层核心,而断层外的变形则以厚度达 40 米的原位破碎岩为主。我们将详细的野外结构勘测与断层岩石的微结构和粒度分布分析相结合,以评估(1)原位破碎岩的形成机制和(2)沿MMF的剪切变形逐渐局部化的机制。在对几种形成机制(力学模型)的可行性进行审查后,所得结果支持以下假设:原位破碎岩的形成与(多次)地震断裂(主震和余震序列)在力学异质断层带内的传播有关。异质性是由于以前的地震造成的破坏,同时也是从较古老的低角度推力断层继承下来的。因此,我们认为这些破碎岩石的起源更符合地震相关过程,而不仅仅是准静态断层生长模型。另一方面,在几个地震周期中,原位破碎岩石体积内的剪切变形逐渐适应,从而产生了巨塑断层核心。我们的结论是,大量原位破碎岩石是几何和力学异质断层带中与地震相关的耗散过程的结果。在这种情况下,大量的原位破碎岩石是符合要求的低速区,会影响地震破裂的传播。
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来源期刊
Journal of Structural Geology
Journal of Structural Geology 地学-地球科学综合
CiteScore
6.00
自引率
19.40%
发文量
192
审稿时长
15.7 weeks
期刊介绍: The Journal of Structural Geology publishes process-oriented investigations about structural geology using appropriate combinations of analog and digital field data, seismic reflection data, satellite-derived data, geometric analysis, kinematic analysis, laboratory experiments, computer visualizations, and analogue or numerical modelling on all scales. Contributions are encouraged to draw perspectives from rheology, rock mechanics, geophysics,metamorphism, sedimentology, petroleum geology, economic geology, geodynamics, planetary geology, tectonics and neotectonics to provide a more powerful understanding of deformation processes and systems. Given the visual nature of the discipline, supplementary materials that portray the data and analysis in 3-D or quasi 3-D manners, including the use of videos, and/or graphical abstracts can significantly strengthen the impact of contributions.
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