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首页> 外文期刊>Tectonophysics: International Journal of Geotectonics and the Geology and Physics of the Interior of the Earth >Seismotectonics of strike-slip earthquakes within the deep crust of southern Italy: Geometry, kinematics, stress field and crustal rheology of the Potenza 1990-1991 seismic sequences (M-max 5.7)
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Seismotectonics of strike-slip earthquakes within the deep crust of southern Italy: Geometry, kinematics, stress field and crustal rheology of the Potenza 1990-1991 seismic sequences (M-max 5.7)

机译：意大利南部深地壳内走滑地震的地震构造学：波坦察1990-1991年地震序列的几何学，运动学，应力场和地壳流变学（M-max 5.7）

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摘要

We present a revision and a seismotectonic interpretation of deep crust strike-slip earthquake sequences that occurred in 19901991 in the Southern Apennines (Potenza area). The revision is motivated by: i) the striking similarity to a seismic sequence that occurred in 2002 similar to 140 km NNW, in an analogous tectonic context (Molise area), suggesting a common seismotectonic environment of regional importance; ii) the close proximity of such deep strike-slip seismicity with shallow extensional seismicity (Apennine area); and iii) the lack of knowledge about the mechanical properties of the crust that might justify the observed crustal seismicity. A comparison between the revised 1990-1991 earthquakes and the 2002 earthquakes, as well as the integration of seismological data with a rbeological analysis offer new constraints on the regional seismotectonic context of crustal seismicity in the Southern Apennines. The seismological revision consists of a relocation of the aftershock sequences based on newly constrained velocity models. New focal mechanisms of the aftershocks are computed and the active state of stress is constrained via the use of a stress inversion technique. The relationships among the observed seismicity, the crustal structure of the Southern Apennines, and the theological layering are analysed along a crustal section crossing southern Italy, by computing geotherms and two-mechanism (brittle frictional vs. ductile plastic strength) theological profiles. The 1990-1991 seismicity is concentrated in a well-defined depth range (mostly between 15 and 23 km depths). This depth range corresponds to the upper pat of the middle crust underlying the Apulian sedimentary cover, in the footwall of the easternmost Apennine thrust system. The 3D distribution of the aftershocks, the fault kinematics, and the stress inversion indicate the activation of a right-lateral strike-slip fault striking N100 degrees E under a stress field characterized by a sub-horizontal N142 degrees-trending sigma 1 and a sub-horizontal N232 degrees-trending sigma 3, very similar to the known stress field of the Gargano seismic zone in the Apulian foreland. The apparent anomalous depths of the earthquakes (> 15 km) and the confinement within a relatively narrow depth range are explained by the crustal rheology, which consists of a strong brittle layer at mid crustal depths sandwiched between two plastic horizons. This articulated theological stratification is typical of the central part of the Southern Apennine crust, where the Apulian crust is overthrusted by Apennine units. Both the Potenza 1990-1.991 and the Molise 2002 seismic sequences can be interpreted to be due to crustal E-W fault zones within the Apulian crust inherited from previous tectonic phases and overthrusted by Apennine units during the Late Pliocene-Middle Pleistocene. The present strike-slip tectonic regime reactivated these fault zones and caused them to move with an uneven mechanical behaviour; brittle seismogenic faulting is confined to the strong brittle part of the middle crust. This strong brittle layer might also act as a stress guide able to laterally transmit the deviatoric stresses responsible for the strike-slip regime in the Apulian crust and may explain the close proximity (nearly overlapping) of the strike-slip and normal faulting regimes in the Southern Apennines. From a methodological point of view, it seems that rather simple two-mechanism rheological profiles, though affected by uncertainties, are still a useful tool for estimating the rheological properties and likely seismogenic beaviour of the crust. (c) 2007 Elsevier B.V. All rights reserved.
机译：我们介绍了1990年在亚平宁山脉南部（波坦察地区）发生的深部地壳走滑地震序列的修订和地震构造解释。修订的动机是：i）与2002年发生的地震序列具有惊人的相似性，在类似的构造背景下（莫利塞地区），与140 km NNW相似，表明该地区具有共同的地震构造环境; ii）这种深的走滑地震活动与浅层延伸地震活动（亚平宁地区）非常接近; iii）缺乏有关地壳力学特性的知识，这些知识可能证明所观察到的地壳地震活动是合理的。修订后的1990-1991年地震与2002年地震之间的比较，以及地震数据与流变学分析的整合，为南亚平宁山脉地壳地震活动的区域地震构造背景提供了新的限制。地震修正包括基于新约束的速度模型对余震序列的重新定位。计算了余震的新震源机制，并通过使用应力反演技术来限制应力的活动状态。通过计算地热和两种机制（脆性摩擦力与延性塑性强度之间的关系）计算地热，分析了观测到的地震活动性，南部亚平宁山脉的地壳结构和神学分层之间的关系。 1990-1991年的地震活动集中在明确定义的深度范围内（通常在15至23 km深度之间）。该深度范围对应于最东端的亚平宁逆冲系统下盘中阿普利亚沉积盖层下方中地壳的上部拍。余震的3D分布，断层运动学和应力反演表明，在以亚水平N142度趋势sigma 1和亚水平N142为特征的应力场下，走向N100度E的右侧走滑断层的激活。 N232水平趋势sigma 3，与阿普利亚前陆加尔加诺地震带的已知应力场非常相似。地壳流变学解释了地震的明显异常深度（> 15 km）和局限在相对较窄的深度范围内，地壳流变学由夹在两个塑性层之间的中地壳深处的坚硬脆性层组成。这种清晰的神学分层是典型的南部亚平宁地壳中部，那里的阿普利亚地壳被亚平宁单元推覆了。 Potenza 1990-1.991和Molise 2002地震序列都可以解释为是从上一个构造相继承而来的阿普利亚地壳内地壳E-W断层带，并在上新世-中更新世晚期被亚平宁单元推覆。目前的走滑构造带重新激活了这些断裂带，并使它们以不均匀的机械行为运动。脆性发震断层仅限于中地壳的强脆部分。这种坚固的脆性层还可以作为应力导向，能够横向传输负责普利亚地壳走滑状态的偏应力，并可以解释走滑和正常断层状态的紧密接近（几乎重叠）。南部亚平宁山脉。从方法学的角度看，虽然受不确定性影响，但相当简单的两机理流变剖面仍然是估算地壳的流变性质和可能的地震成因的有用工具。 （c）2007 Elsevier B.V.保留所有权利。

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