Establishment of a Non-Permanent GPS Network to Monitor the Recent NE-SW Deformation in the Granada Basin (Betic Cordillera,Southern Spain)

The Granada Basin (Central Betic Cordillera), one of the most seismically active areas of the Iberian Peninsula, is currently subjected to NW-SE compression and NE-SW extension. The present day extension is accommodated by normal faults with various orientations but particularly with a NW-SE strike. At the surface, these active NW-SE normal faults are mainly concentrated on the NE part of the Basin. In this part we have selected a 15-km long segment where several active normal faults crop out. Using the marine Tortonian rocks as a reference, we have calculated a minimum extensional rate of 0.15-0.30 mm/year. The observed block rotation, the listric geometry of faults at depth and the distribution of seismicity over the whole Basin, indicate that this rate is a minimum value. In the framework of an interdisciplinary research project a non-permanent GPS-network has been established in the central sector of Betic Cordillera to monitor the crustal deformations. The first two observation campaigns were done in 1999 and 2000.     

Tectonic setting of the recent damaging seismic series in the Southeastern Betic Cordillera,Spain

In this work we analyze the tectonic setting of the recent damaging seismic series occurred in the Internal Zones of the eastern Betic Cordillera (SE Spain) and surrounding areas, the tectonic region where took place the 11th May 2011 Mw 5.2 Lorca earthquake. We revisit and make a synthesis of the seven largest and damaging seismic series occurred from 1984 to 2011. We analyze their seismotectonic setting, and their geological sources under the light of recent advances in the knowledge on active faults, neotectonics, seismotectonics and stress regime, with special attention focused on the Lorca Earthquake. These seismic series are characterized by two types of focal mechanisms, produced mainly by two sets of active faults, NNW–SSE to NNE–SSW small (no larger than 20–30 km) extensional faults with some strike slip component, and E–W to NE–SW large strike slip faults (more than 50 km long) with some compressional component (oblique slip faults). The normal fault earthquakes related to the smaller faults are dominant in the interior of large crustal tectonic blocks that are bounded by the large E–W to NE–SW strike-slip faults. The strike slip earthquakes are associated to the reactivation of segments or intersegment regions of the large E–W to NE–SW faults bounding those crustal tectonic blocks. Most of the seismic series studied in this work can be interpreted as part of the background seismicity that occurs within the crustal blocks that are strained under a transpressional regime driven by the major strike slip shear corridors bounding the blocks. The seismotectonic analysis and the phenomenology of the studied series indicate that it is usual the occurrence of damaging compound earthquakes of M  \(\sim \)  5.0 associated with triggering processes driven by coseismic stress transfer. These processes mainly occur in the seismic series generated by NNW–SSE to NNE–SSW faults. These mechanical interaction processes may induce a higher frequency of occurrence of this kind of earthquakes than considered in traditional probabilistic seismic hazard assessments and it should be taken into account in future seismic hazard assessments.     

Intramontane basin development related to contractional and extensional structure interaction at the termination of a major sinistral fault: The Huércal-Overa Basin (Eastern Betic Cordillera)

Among the classical minor structural associations on the termination of transcurrent faults are horsetail splays formed by reverse, normal or strike-slip faults developing duplexes. However, temporal and spatial coexistence of contractional and extensional structures is very rarely documented. We discuss the relationships of contractional and extensional structures and associated sedimentary depocenters at the termination of a major strike-slip fault in the Eastern Betic Cordillera. Field mapping, kinematic fault analysis, paleostress determination and gravity prospecting in the Huércal-Overa Basin, at the southern termination of the NE–SW Alhama de Murcia transcurrent fault (AMF), are used to establish the relationships of tectonic structures and associated sedimentary depocenters. Here, ENE–WSW and WNW–ESE folds interact with two sets of normal faults having the same orientation as well as ENE–WSW reverse faults. Progressive unconformities associated with folds reveal that the beginning of the AMF activity occurred in the Tortonian. The folds progressively grew and rotated from ENE–WSW up to WNW–ESE close to the transcurrent fault. We propose that the development of the normal faults developed during short-term episodes characterized by vertical major stress axis and are, in turn, related to gravitational instability linked to the thickening of a crust relatively hot at depth. This setting may have become predominant in between the main activity, compressive pulses along transcurrent faults.     

黏滑断层隧道减错措施参数对减错效果的影响分析

为提高黏滑断层隧道的结构安全性和稳定性,对黏滑断层隧道设置不同缝宽减错缝、不同刚度减错层的减错效果进行研究。研究结果表明:断层黏滑错动对上盘隧道的影响远大于下盘;减错缝对上盘部分隧道结构的减错效果优于下盘,其中上盘减错效果最大为24.50%,下盘减错效果最大为9.26%;减错层对下盘部分隧道结构的减错效果略优于上盘,其中下盘减错效果最大为105.32%,上盘减错效果最大为78.07%;随着减错缝宽度的增加,隧道上盘减错效果变好,下盘缝宽10—15cm减错效果最好;随着减错层弹性模量的增加,隧道上下盘减错效果降低,当减错层弹性模量增加到一定程度（约100MPa）,减错效果趋于稳定。研究成果可为黏滑断层隧道的减错结构设计及施工提供参考。     

PS-InSAR processing methodologies in the detection of field surface deformation—Study of the Granada basin (Central Betic Cordilleras,southern Spain)

Differential SAR interferometry (DInSAR) is a very effective technique for measuring crustal deformation. However, almost all interferograms include large areas where the signals decorrelate and no measurements are possible. Persistent scatterer interferometry (PS-InSAR) overcomes the decorrelation problem by identifying resolution elements whose echo is dominated by a single scatterer in a series of interferograms.Two time series of 29 ERS-1/2 and 22 ENVISAT ASAR acquisitions of the Granada basin, located in the central sector of the Betic Cordillera (southern Spain), covering the period from 1992 to 2005, were analyzed. Rough topography of the study area associated to its moderate activity geodynamic setting, including faults and folds in an uplifting relief by the oblique Eurasian–African plate convergence, poses a challenge for the application of interferometric techniques. The expected tectonic deformation rates are in the order of ～1 mm/yr, which are at the feasibility limit of current InSAR techniques.In order to evaluate whether, under these conditions, InSAR techniques can still be used to monitor deformations we have applied and compared two PS-InSAR approaches: DePSI, the PS-InSAR package developed at Delft University of Technology (TU Delft) and StaMPS (Stanford Method for Persistent Scatterers) developed at Stanford University. Ground motion processes have been identified for the first time in the study area, the most significant process being a subsidence bowl located at the village of Otura.The idea behind this comparative study is to analyze which of the two PS-InSAR approaches considered might be more appropriate for the study of specific areas/environments and to attempt to evaluate the potentialities and benefits that could be derived for the integration of those methodologies.     

Local earthquakes seismic tomography in the Betic Cordillera (southern Spain)

A crustal tomographic image, from the surface down to 35 km depth beneath the Betic Cordillera (southern Spain), is obtained using data on local earthquakes recorded at stations from the National and Andalusian Seismic Networks. The velocity structure and the hypocentre locations are derived from the inversion of P first arrival times, using an iterative simultaneous inversion method. The reliability of the results is assessed using different control parameters. The inverted velocity field in the uppermost layers shows a significant lateral variability which reflects most of the large-scale geological features of the Betic Cordillera. Well determined local surface anomalies allow to constrain the location and geometry of the most prominent Neogene sedimentary basins. The upper crust is well resolved throughout the whole region, and is characterized by relatively high velocities in the Internal Betics and in the South Iberian Massif and lower velocities within the External Betics. A relatively well constrained event cluster displays a NNE–SSW trend, and outlines the contact zone between the Internal and the External domains. The middle and lower crustal levels show reliable results beneath the central part of the Betic Cordillera. High averaged velocities are obtained within the South Iberian and the Alboran domains, in contrast to a relatively low velocity anomaly which characterizes the boundary between them. These findings support the hypothesis of the lack of well differentiated crustal levels below the contact zone, while crustal layering is better defined beneath the Alboran and the Iberian domains.     

The North Cycladic Detachment System

Low-angle normal faults accommodate a large part of continental post-orogenic extension. Besides the intrinsic rheological characteristics of the continental crust that may lead to the formation of shallow-dipping shear zones at the brittle–ductile transition, the role of pre-existing low-angle structures such as large thrusts has been proposed by several authors. We explore this question with the example of the North Cycladic Detachment System (NCDS) that is composed of a series of distinct detachments cropping out on the islands of Andros, Tinos and Mykonos, separating the Cycladic Blueschists in the footwall from the Upper Cycladic Nappe in the hanging wall. We show that these extensional structures are part of a single large-scale structure (more than 200 km along strike) that reactivates the Vardar suture zone. It extends eastward on Ikaria and westward offshore Evia and Thessalia where it probably connects to recent shallow-dipping normal faults evidenced on published seismic reflection profiles. The NCDS started its activity in the Oligocene concommitantly with the Aegean extension, and was still active in the Late Miocene. It has exhumed a series of metamorphic domes from southern Evia to Mykonos below low-angle detachment systems, made of low-angle normal faults and low-angle ductile shear zones. The ductile shear zones and the faults were created with a low dip and they kept the same attitude throughout their exhumation. We identify three main detachments that are part of a continuum of extension on the NCDS : Tinos detachment, Livada detachment and Mykonos detachment. A fourth detachment (Vari detachment) is the reactivation of an Eocene exhumation-related structure. Deformation in the footwall is characterized by intense stretching and flattening. Using the spatial evolution observed along strike from Andros to Mykonos we construct a history of formation of the NCDS starting with the reactivation of former thrusts leading to the exhumation of high-temperature metamorphic domes. The Aegean example shows that reactivation of earlier shallow-dipping discontinuities can play a fundamental role in continental post-orogenic extension.     

Main features of the deep structure by local earthquake tomography and active tectonics: case of Rif Mountain (morocco) and Betic Cordillera (Spain)

Within the Spain and Moroccan networks, a large volume of seismic data has been collected and used for investigating the lithosphere in the Betic–Rif Cordillera. The present study has two main goals: (1) Use the most actual seismological data from recent earthquakes in the Betic–Rif arc for investigating the lithosphere through the application of seismic local tomography techniques. (2) Define the possible structural blocks and explain the GPS velocities perturbation in this region. The resolution tests results indicate that the calculated images gave a close true structure for the studied regions from 5- to 60-km depth. The resulting tomographic image shows that the presence of two upper crust body (velocity 6.5 km/s) at 3- to 13-km depth between Iberian Betic and Moroccan Rif in the western and in the middle of Alboran Sea also shows the low velocity favoring the presence of melt in the base of these two bodies. The crustal bodies forms tectonic blocks in the Central Rif and in the Central Betic Cordillera.     

THE RESEARCH OF THE SEISMOGENIC STRUCTURE OF THE LUSHAN EARTHQUAKE BASED ON THE SYNTHESIS OF THE DEEP SEISMIC DATA AND THE SURFACE TECTONIC DEFORMATION

The seismogenic structure of the Lushan earthquake has remained in suspensed until now. Several faults or tectonics, including basal slipping zone, unknown blind thrust fault and piedmont buried fault, etc, are all considered as the possible seismogenic structure. This paper tries to make some new insights into this unsolved problem. Firstly, based on the data collected from the dynamic seismic stations located on the southern segment of the Longmenshan fault deployed by the Institute of Earthquake Science from 2008 to 2009 and the result of the aftershock relocation and the location of the known faults on the surface, we analyze and interpret the deep structures. Secondly, based on the terrace deformation across the main earthquake zone obtained from the dirrerential GPS meaturement of topography along the Qingyijiang River, combining with the geological interpretation of the high resolution remote sensing image and the regional geological data, we analyze the surface tectonic deformation. Furthermore, we combined the data of the deep structure and the surface deformation above to construct tectonic deformation model and research the seismogenic structure of the Lushan earthquake. Preliminarily, we think that the deformation model of the Lushan earthquake is different from that of the northern thrust segment ruptured in the Wenchuan earthquake due to the dip angle of the fault plane. On the southern segment, the main deformation is the compression of the footwall due to the nearly vertical fault plane of the frontal fault, and the new active thrust faults formed in the footwall. While on the northern segment, the main deformation is the thrusting of the hanging wall due to the less steep fault plane of the central fault. An active anticline formed on the hanging wall of the new active thrust fault, and the terrace surface on this anticline have deformed evidently since the Quaterary, and the latest activity of this anticline caused the Lushan earthquake, so the newly formed active thrust fault is probably the seismogenic structure of the Lushan earthquake. Huge displacement or tectonic deformation has been accumulated on the fault segment curved towards southeast from the Daxi country to the Taiping town during a long time, and the release of the strain and the tectonic movement all concentrate on this fault segment. The Lushan earthquake is just one event during the whole process of tectonic evolution, and the newly formed active thrust faults in the footwall may still cause similar earthquake in the future.     

褶皱陡坎中相关断层在缩短量计算中的作用——以东秋里塔格背斜为例

通过对东秋里塔格背斜地区内与褶皱陡坎伴生的次级断层进行的地质调查,确定了该次级断层属于伸出向斜的逆冲断层,也给出了次级断层的发生时间晚于褶皱作用起始时间的1个变形实例。褶皱陡坎中发育的次级断层使得陡坎上盘地层沿断层面整体向上迁移,不仅次级断层使得阶地面发生掀斜并增大褶皱陡坎的坡度,而且直接影响了区域缩短增量计算的真实性。计算结果显示,当不考虑次级断层对褶皱陡坎高度的影响时,计算所得缩短增量为51.42m,考虑次级断层对褶皱陡坎高度的影响时,计算得到的地壳缩短量为45.23m。二者相差6.19m,偏差占总缩短增量的13.7%,是一个不可忽视的量值。东秋里塔格背斜北翼和南翼的褶皱陡坎发育于相同岩性的基岩中而且具有相同的形成机制。但是背斜北翼在水平距离不足300m的范围内发育了3级褶皱陡坎,这表明北翼相对于南翼,其活动枢纽带更为紧闭。这是由于北翼存在更加强烈的挤压应力及更加快速的隆升作用。因此,次级断层的研究对于正确认识区域构造演化、了解褶皱与断层相互作用关系具有重要意义。但是仍存在很多问题:1)受观察剖面范围有限、次级断层分布不连续和断距沿延伸方向不断增大等因素的制约,次级断层对缩短增量造成的影响可能被低估,计算结果应为缩短量的最小值。2)次级断层增加的陡坎高度与断层的断距、倾角具有怎样的定量关系?3)若次级断层只发育于活动枢纽带内,又会产生怎样的影响?这些问题还需更多的研究实例来进行更加深入的研究。     

跨黏滑断层隧道纤维混凝土衬砌抗错断技术研究

为提高跨黏滑断层隧道的结构安全性和稳定性,以都汶高速友谊隧道F 1黏滑断层段为研究背景,通过采用纤维混凝土衬砌对跨黏滑断层隧道抗错断技术进行研究。结果表明:同体积纤维掺量条件下,混杂纤维混凝土(SBFRC)立方体抗压强度比纤维混凝土(SFRC)略低,SBFRC抗折强度比SFRC略高;断层黏滑错动对隧道上盘的影响大于下盘;纤维混凝土衬砌对下盘隧道结构的抗错效果优于上盘隧道,SFRC二衬平均抗错效果为12.22%,SBFRC二衬平均抗错效果为15.81%。研究成果可为黏滑断层隧道的结构设计及施工提供参考。     

宁夏吴忠地区北部的浅部结构和隐伏断裂——地震反射剖面结果

应用浅层地震勘探法对宁夏吴忠地区北部的浅部地壳结构和隐伏活动断裂进行研究。结果表明,该区存在2条隐伏断裂,分别为银川主断层南段和新华桥断层。推测银川主断层南段为近SN走向的W倾正断层,断层下盘地层界面一般呈近水平状展布,而在断层上盘,T_Q及其以下的地层界面向断面方向倾伏并显示出逆牵引现象,断层向上错断了第四系内部。钻孔联合地质剖面及浅层地震探测结果共同揭示新华桥断层为一条走向NE,倾向SW的正断层,深、浅地震测线控制的新华桥断层延伸长度9 km左右,向上错断了第四系内部的T_(02)界面。     

中国及邻区现代构造形变特征

本文根据大量浅源地震机制解, 地面地震地质调查、资源卫星影像判读和其它地球物理资料、讨论了我国及其邻区现代构造形变的区域特征.它具体反映在我国东部地区, 现代构造形变是以剪切破裂为主, 断层活动多为北北东—北东向的右旋走滑性质, 也有与之共轭的北西西—北西向的左旋走滑性质的断层活动.西部地区则以压缩形变为特征, 主要表现在以青藏高原为主体的凸向东北的四重弧形构造带上, 在第一和第四弧形带的东北部以挤压引起的逆断层活动为主, 第二和第三弧形带是在挤压作用下, 由于物质的横向推移而引起的走滑断层活动.此外现代构造形变的区域特征还反映在地壳厚度的分布轮廓上.造成我国及邻区这样一种现代构造形变特征的原因是与周围几个板块运动有密切关系的.      

Mountain Front Development by Folding and Crustal Thickening in the Internal Zone of the Betic Cordillera-Alboran Sea Boundary

The boundary between the Alboran Sea and Betic Cordillera is a good example of a fold related mountain front in the Internal Zone of an alpine mountain range. Since the late Miocene, NNW-SSE convergence between the Eurasian and African plates has produced shortening and related orthogonal extension. To improve the characterisation of the geometry of the deep structure in the region and to establish the recent tectonic evolution of the mountain front, well logs and newly acquired geophysical data (multichannel reflection seismic and gravimetric surveys) have been interpreted and integrated with available surface data. The most marked tectonic structure corresponds to large antiforms and synforms of ENE-WSW trend which are related to mountain ranges and basins, respectively. The fold belt continues toward the northern continental shelf of the Alboran Sea. The fold vergence is generally northwards and its amplitude decreases progressively towards SSE, until disappearring in a sharp boundary where the reflectors are undeformed. The deep geometry suggests that fold growth started during upper Tortonian times and continued its activity up to Pliocene or even Quaternary times. The NNW-SSE compression produces crustal thickening and a regional and progressive southwards emersion. The location of main present-day deformation fronts in the Internal Zones contrasts with classical models where the deformation progresses towards the frontal part of External Zones of cordilleras. In addition, this fold-related deformation mountain front has features different from fault related fronts, as it does not show a sharp boundary, and folds that determine rectilinear mountain boundaries decrease progressively in amplitude or in wavelength up to undeformed areas.     

倾斜断层不对称分布引起的几何效应-上下盘效应.

首先介绍了具有加权平均意义的均方根距离Drms. 与断层距Drup和发震断层距Dseis相比, 均方根距离可以真实地反映观测点与倾斜断层的整体靠近程度. 然后利用断层距、 发震断层距和均方根距离, 通过回归分析分别对1999年集集地震加速度峰值的上下盘效应进行研究. 残差分析表明上盘的加速度峰值明显大于相同断层距或发震断层距处下盘的加速度峰值, 而相同均方根距离处的上下盘观测点的加速度峰值没有明显差异. 这说明上下盘效应是一种由于倾斜断层的不对称分布引起的几何效应, 因此进行地震动衰减分析时, 如果采用均方根距离作为观测点与断层之间的距离标准, 上下盘效应对近断层地震动的影响可以忽略.      

利用强震数据获取汶川地震近断层地面永久位移

利用汶川地震中得到的靠近映秀—北川主断裂的64个强震台站的三分量记录数据, 对加速度记录进行基线校正的基础上获取近断层地面运动的永久形变位移, 并将由强震记录获取到的地面位移结果与GPS观测到的同震位移进行对比分析, 研究汶川M_S8.0地震的近断层地面运动的位移特征. 结果表明: ① 在靠近映秀—北川主断层的上盘和下盘, 东西相向的地面运动非常剧烈. 下盘的51SFB, 51MZQ和51JYH台东西向位移均为负(即地面运动向西), 其中51SFB台位移量最大, 达到1.49 m; 上盘的51WCW台位移向东, 位移量为1.26 m. ② 地面运动的位移分布主要表现为以龙门山断裂带的映秀—北川断裂为核心的相向运动, 东西方向上的永久位移要大于南北方向. 从断层机制上来讲, 断层的错动以逆冲运动为主(即逆冲位移要大于走滑分量的位移), 这与震源机制反演及地质考察的结果一致. ③ 大的地面永久位移集中分布在以龙门山断裂带为中心的狭长范围内, 离开发震断裂地面位移的衰减很快. 相比而言, 在发震断层的下盘一侧(即四川盆地)的地面位移的衰减比上盘一侧明显要快.      

Effects of hanging wall and forward directivity in the 1999 Chi-Chi earthquake on inelastic displacement response of structures

The characteristics of the inelastic response of structures affected by hanging wall and forward directivity in the 1999 Chi-Chi earthquake are investigated. Inelastic displacement ratios (IDRs) for ground motions impacted by these near- field effects are evaluated and comprehensively compared to far-field ground motions. In addition, the inelastic displacement responses to hanging wall and footwall ground motions are compared. It is concluded that the inelastic displacement response is significantly affected in the short period range by hanging wall and in the long period range by footwall. Although high peak ground acceleration was observed at hanging wall stations, the IDRs for structures on hanging wall sites are only larger than footwall sites in the very long period range. Forward directivity effects result in larger IDRs for periods longer than about 0.5s. Adopting statistical relationships for IDRs established using far-field ground motions may lead to either overestimation or underestimation in the seismic evaluation of existing structures located in near-field regions, depending on their fundamental vibration periods.     

汶川地震中强震动相对持时的空间变化特性研究

使用70％和90％能量持时定义,计算了汶川Ms8.0大地震中获取的来自109个台站强震动加速度记录的相对持时,并以此在竖向及两个水平向上分别进行了回归统计分析,得到了地震动持时的空间变化关系,给出了适合汶川地震地震动的持时定义.对比分析了上盘和下盘2个区域持时空间变化特征,进一步计算了地震动竖向持时与两个水平向持时的比...     

Internal structure of the Nojima Fault zone from the Hirabayashi GSJ drill core

Abstract The internal structures of the Nojima Fault, south-west Japan, are examined from mesoscopic observations of continuous core samples from the Hirabayashi Geological Survey of Japan (GSJ) drilling. The drilling penetrated the central part of the Nojima Fault, which ruptured during the 1995 Kobe earthquake (Hyogo-ken Nanbu earthquake) ( M 7.2). It intersected a 0.3 m-thick layer of fault gouge, which is presumed to constitute the fault core (defined as a narrow zone of extremely concentrated deformation) of the Nojima Fault Zone. The rocks obtained from the Hirabayashi GSJ drilling were divided into five types based on the intensities of deformation and alteration: host rock, weakly deformed and altered granodiorite, fault breccia, cataclasite, and fault gouge. Weakly deformed and altered granodiorite is distributed widely in the fault zone. Fault breccia appears mostly just above the fault core. Cataclasite is distributed mainly in a narrow (≈1 m wide) zone in between the fault core and a smaller gouge zone encountered lower down from the drilling. Fault gouge in the fault core is divided into three types based on their color and textures. From their cross-cutting relationships and vein development, the lowest fault gouge in the fault core is judged to be newer than the other two. The fault zone characterized by the deformation and alteration is assumed to be deeper than 426.2 m and its net thickness is > 46.5 m. The fault rocks in the hanging wall (above the fault core) are deformed and altered more intensely than those in the footwall (below the fault core). Furthermore, the intensities of deformation and alteration increase progressively towards the fault core in the hanging wall, but not in the footwall. The difference in the fault rock distribution between the hanging wall and the footwall might be related to the offset of the Nojima Fault and/or the asymmetrical ground motion during earthquakes.     

夏垫活动断层土壤氡地球化学特征

夏垫活动断层为首都圈重要的断层之一。本文用土壤中气氡测量法在齐心庄和东柳河屯区段进行了野外现场勘测,揭示了研究区土壤氡的地球化学异常,绘制出研究区的氡浓度等值线图,分析了该区段活动断层的上下盘、空间位置及断层走向,并探讨了研究区断裂带的规模及活动性。综合分析认为,断裂带规模较大和断层活动性较强的齐心庄处的夏垫活动断层应为今后地震监测的重点。