Present activity and seismogenic potential of a low-angle normal fault system (Citta di Castello, Italy): Constraints from surface geology, seismic reflection data and seismicity
Present activity and seismogenic potential of a low-angle normal fault system (Citta di Castello, Italy): Constraints from surface geology, seismic reflection data and seismicity
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DOI：
10.1016/j.tecto.2008.09.023
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发表时间：
2009-01-01
期刊：
影响因子：
2.9
通讯作者：
Pace, Bruno
中科院分区：
文献类型：
--
作者：
Brozzetti, Francesco;Boncio, Paolo;Pace, Bruno
我们对意大利亚平宁北部卡斯特罗-桑塞波尔克罗盆地(CSB)的活动低角度正断层系统提出了新的约束条件。来自Carta Geologica d‘talia(CARG项目)地质调查的新野外数据确定了正常断层系统的表面几何形状，并导致对CROC03深地壳地震反射剖面(Castiglion Fiorentino-Urbania段)的解释，其中特别关注了Plio-第四纪伸展结构的几何形状。地表和地下地质资料与仪器和历史地震活动相结合，以确定该地区的地震构造。低角度东倾反射体是著名的Altotiberina断层(AF)的地震表达，AF是一种区域伸展滑脱，其上同时存在东西倾斜的高角度断层，边界为CSB。AF分离区位于CSB以西约10公里处。在伸展的异长花岗岩中，合成的东倾面占优势。沿AF的位移约为4.5公里，这与其合成展布造成的累积偏移量一致。至少自早更新世以来，CSB的演化主要受东倾断裂系统的控制，该系统至今仍是活跃的，并对该区的地震活动负责。CSB内部记录的地震活动水平很低，但历史上曾发生过几次破坏性地震。根据历史上最大地震(5次最大MCS烈度为IX到IX-X的地震)的仪器地震活动性和烈度数据点，我们可以提出两个主要的发震构造：蒙特圣玛丽亚台地(Mmax=5.9)和卡斯特罗(Citta di Castello，Mmax高达6.5)正断层。两者都是房颤剥离的合成展布，以中等(45-50度)到低(25-30度)的角度向东北倾斜，并将上地壳切割到地表。这项研究表明，低角度正断层(至少倾角为25-30度)可能是地震的发源地。(C)2008爱思唯尔B.V.保留所有权利。
We present new constraints on an active low-angle normal fault system in the Citta di Castello-Sansepolcro basin (CSB) of the northern Apennines of Italy. New field data from the geological survey of the Carta Geologica d'talia (CARG project) define the surface geometry of the normal fault system and lead to an interpretation of the CROP 03 deep-crust seismic reflection profile (Castiglion Fiorentino-Urbania segment), with particular attention paid to the geometry of the Plio-Quaternary extensional structures. Surface and sub-surface geological data are integrated with instrumental and historical seismicity in order to define the seismotectonics of the area.Low-angle east-dipping reflectors are the seismic expression of the well-known Altotiberina Fault (AF), a regional extensional detachment on which both east- and west-dipping high-angle faults, bounding the CSB, sole out. The AF breakaway zone is located similar to 10 km west of the CSB. Within the extensional allochthon, synthetic east-dipping planes prevail. Displacement along the AF is similar to 4.5 km, which agrees with the cumulative offset due to its synthetic splays. The evolution of the CSB has mainly been controlled by the east-dipping fault system, at least since Early Pleistocene time; this system is still active and responsible for the seismicity of the area. A low level of seismic activity was recorded instrumentally within the CSB, but several damaging earthquakes have occurred in historical times. The instrumental seismicity and the intensity data points of the largest historical earthquakes (5 events with maximum MCS intensity of IX to IX-X) allow us to propose two main seismogenic structures: the Monte Santa Maria Tiberina (Mmax=5.9) and Citta di Castello (Mmax up to 6.5) normal faults. Both are synthetic splays of the AF detachment, dipping to the NE at moderate (45-50 degrees) to low (25-30 degrees) angles and cutting the upper crust up to the surface. This study suggests that low-angle normal faults (at least with dips of 25-30 degrees) may be seismogenic. (c) 2008 Elsevier B.V. All rights reserved.