datasheet2_Fault Pattern and Seismotectonic Style of the Campania – Lucania 1980 Earthquake (Mw 6.9, Southern Italy): New Multidisciplinary Constraints.zip

New fault trace mapping and structural survey of the active faults outcropping within the epicentral area of the Campania-Lucania 1980 normal fault earthquake (Mw 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 ∼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.

针对1980年坎帕尼亚-卢卡尼亚正断层地震（矩震级Mw 6.9）震中区域内出露的活动断层，本研究开展了全新的断层迹线填图与构造勘测工作，并整合了已有地震数据的修订成果，以及对CROP-04近垂直地震剖面的最新解译结果，以此重建发震断层系统的地表与深部几何形态、运动学特征及应力张量。研究识别并刻画了3条主要断层带，它们由数千米长的高角度雁列（en-echelon）段组成。其中内侧与中间断层带分别为伊尔皮尼亚内侧断层（Inner Irpinia, InIF）与伊尔皮尼亚断层（Irpinia Faults, IF），均向东倾；外侧的反向断层（Antithetic Fault, AFA）则向西倾。伊尔皮尼亚内侧断层与伊尔皮尼亚断层的北段与中段走向为NW-SE向，南段则转向W-E向，延伸长度至少16千米。本研究为E-W向段上此前未被识别的地表同震断层作用（最大位移可达1米）提供了证据，并记录了40年前其他研究者已勘测区域内的同震破裂，其最大垂直位移可达约1米。基于地表获取的断层与滑动数据，以及1980年至2018年震源机制的新汇编数据集，本研究开展了应变与应力分析，结果表明，随时间推移及不同地壳深度下均存在一致的NNE向最小主应力；同时发现意大利亚平宁山脉区域存在偏离经典SW-NE张应力方向的地壳尺度偏差。研究结合CROP-04剖面的追踪数据与现有震源分布，分析了出露断层的深部延伸情况。整合所有信息后，本研究构建了延伸至发震层底部的三维地震构造模型。该模型呈现出地堑状构造：在10~12千米以浅的深度，于一条向NE至E倾的伸展型基底拆离体的上盘位置，发育了向南的E-W向弯折段。本研究认为，该构造格局对1980年地震破裂过程中的应力转移起到了控制作用，同时为发生于20秒处的第二次子事件提供了全新解译。本研究的重建结果表明，第二次子事件以两幕连续破裂的形式，分别错断了E-W向主断层段上盘的NNE向倾伏分支断层，以及可能存在的反向SSW向倾伏分支断层。