Fault Pattern and Seismotectonic Style of the Campania - Lucania 1980 Earthquake (Mw 6.9, Southern Italy): New Multidisciplinary Constraints
Fault Pattern and Seismotectonic Style of the Campania - Lucania 1980 Earthquake (Mw 6.9, Southern Italy): New Multidisciplinary Constraints
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DOI：
10.3389/feart.2020.608063
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发表时间：
2021-01-20
影响因子：
2.9
通讯作者：
Lavecchia, G.
中科院分区：
文献类型：
--
作者：
Bello, S.;de Nardis, R.;Lavecchia, G.
对坎帕尼亚-卢卡尼亚1980年正断层地震(M-W 6.9)震中出露的活动断层进行了新的断层追踪填图和构造调查，并结合已有地震资料的修订和CROP-04近垂直地震剖面的最新解释，重建了发震断层模式的地表和深度几何、运动学和应力张量。识别和表征了三条主要的断层排列，这些断层排列成几公里长的高角度梯形段。内部和中间断裂，即内伊尔皮尼亚断裂(INIF)和伊尔皮尼亚断裂(IF)向东倾斜，外对向断裂(AFA)向西倾斜。INIF和IF沿北段和中段向西北-东南方向移动，并沿南段向W-E方向旋转至少16公里。我们提供了沿东西方向的地表同震断层(高达1米)以前未被识别的证据，并记录了最大垂直位移高达1米的同震破裂，这是40年前其他研究人员已经调查过的。来自地表数据的断层/滑动数据和新汇编的震源机制(1980-2018年)用于应变和应力分析，以显示在不同地壳深度随时间一致的NNE向最小主应力，地壳尺度偏离意大利亚平宁山脉典型的西南-东北向张拉方向。分析了露头断层沿CROP-04剖面的深部延展性，并给出了地震震源分布。综合所有信息，建立了三维地震构造模型，并外推到孕震层的底部。它勾勒出在伸展的NE向至E向倾斜的伸展基底拆离的上盘，发育南东向东西弯曲的地块状构造，其深度小于10-12公里。在我们的解释中，这种构造意味着1980年地震破裂时应力传递的控制，并对发生在S 20时的第二次次事件提供了新的解释。我们的重建表明，后者在两个顺序幕中破裂了东西走向主断裂段的上盘NNE倾角展布，也可能是相反的SSW倾角展布。
New fault trace mapping and structural survey of the active faults outcropping within the epicentral area of the Campania-Lucania 1980 normal fault earthquake (M-w 6.9) are integrated with a revision of pre-existing earthquake data and with an updated interpretation of the CROP-04 near-vertical seismic profile to reconstruct the surface and depth geometry, the kinematics and stress tensor of the seismogenic fault pattern. Three main fault alignments, organized in high-angle en-echelon segments of several kilometers in length, are identified and characterized. The inner and intermediate ones, i.e. Inner Irpinia (InIF) and Irpinia Faults (IF), dip eastward; the outer Antithetic Fault (AFA) dips westward. Both the InIF and the IF strike NW-SE along the northern and central segments and rotate to W-E along the southern segments for at least 16 km. We provide evidence of surface coseismic faulting (up to 1 m) not recognized before along the E-W segments and document coseismic ruptures with maximum vertical displacement up to similar to 1 m where already surveyed from other investigators 40 years ago. Fault/slip data from surface data and a new compilation of focal mechanisms (1980 - 2018) were used for strain and stress analyses to show a coherent NNE-directed least principal stress over time and at different crustal depths, with a crustal-scale deviation from the classic SW-NE tensional direction across the Apennines of Italy. The continuation at depth of the outcropping faults is analyzed along the trace of the CROP-04 profile and with available hypocentral distributions. Integrating all information, a 3D seismotectonic model, extrapolated to the base of the seismogenic layer, is built. It outlines a graben-like structure with a southern E-W bend developed at depth shallower than 10-12 km, at the hanging wall of an extensional NE- to E-dipping extensional basal detachment. In our interpretation, such a configuration implies a control in the stress transfer during the 1980 earthquake ruptures and provides a new interpretation of the second sub-event, occurred at 20 s. Our reconstruction suggests that the latter ruptured a hanging wall NNE-dipping splay of the E-W striking main fault segment and possibly also an antithetic SSW-dipping splay, in two in-sequence episodes.