An investigation of the active tectonics in central-eastern mainland Greece with imaging and decomposition of topographic and aeromagnetic data

We report the results of a joint analysis of aeromagnetic, topographic and tectonic data in central-eastern mainland Greece. The emphasis of the analysis is placed on the detection of coherent lineations (discontinuities), collocated and correlated with faulting structures detected by geological field observation. To this effect, edge detection and image enhancement were applied to digital aeromagnetic anomaly maps and digital elevation models, comprising bidirectional differentiation, wavelet transformation (imaging) and spatial decomposition/reconstruction in the wavenumber domain. The analysis facilitated the detection of significant topographic lineaments with NNE–SSW, ENE–WSW and ESE–WNW orientations. Respectively, the aeromagnetic data exhibit two families of significant NE–SW, and one family of ESE–WNW lineaments. The major aeromagnetic and topographic lineaments coincide and have comparable width scales of the order of 2–3 km, indicating that they are produced by significant discontinuities in the upper crust. The kinematics of the NE–SW faults varies between oblique-slip and strike-slip. These faults affect Neogene to Late Quaternary deposits and have been responsible for the formation of transverse depressions and horsts. This is also corroborated by focal plane solutions from small earthquakes recorded by local networks. The nature of these structures is not yet clear. However, they have been detected by diverse methodologies, they have considerable extent and are apparently active. These attributes suggest that they may possibly be related to the propagation and diffusion of the North Anatolian and North Aegean fault systems into the Greek mainland.     

Plio-Quaternary paleostresses in the Atlantic passive margin of the Moroccan Meseta: Influence of the Central Rif escape tectonics related to Eurasian-African plate convergence

The Atlantic Moroccan Meseta margin is affected by far field recent tectonic stresses. The basement belongs to the variscan orogen and was deformed by hercynian folding and metamorphism followed by a post-Permian erosional stage, producing the flat paleorelief of the region. Tabular Mesozoic and Mio-Plio-Quaternary deposits locally cover the Meseta, which has undergone recent uplift, while north of Rabat the subsidence continues in the Gharb basin, constituting the foreland basin of the Rif Cordillera.The Plio-Quaternary sedimentary cover of the Moroccan Meseta, mainly formed by aeolian and marine terraces deposits, is affected by brittle deformations (joints and small-scale faults) that evidence that this region – considered up to date as stable – is affected by the far field stresses. Striated faults are recognized in the oldest Plio-Quaternary deposits and show strike-slip and normal kinematics, while joints affect up to the most recent sediments.Paleostress may be sorted into extensional, only affecting Rabat sector, and three main compressive groups deforming whole the region: (1) ENE–WSW to ESE–WNW compression; (2) NNW–SSE to NE–SW compression and (3) NNE–SSW compression. These stresses can be attributed mainly to the NW–SE oriented Eurasian-African plate convergence in the western Mediterranean and the escape toward the SW of the Rif Cordillera. Local paleostress deviations may be related to basement fault reactivation. These new results reveal the tectonic instability during Plio-Quaternary of the Moroccan Meseta margin in contrast to the standard passive margins, generally considered stable.     

近场精确定位在卢龙MemLsub6.2地震发震构造研究中的应用

从1982年10月19日卢龙6.2级地震余震近场数字地震资料的391条记录中， 挑选出可用于精确定位的171条地震事件记录，采用Hypoinverse定位方法对45个事件进行了重定位. 精确定位的震中分布显示出一卧倒的反ldquo;Frdquo;形活动地震构造的形态， 两条NNE向断裂被一条WNW向断裂所截断，两组断裂呈脆性断裂常见的共轭状态产出， NNE向的断层正在相互贯通，卢龙附近的滦河河谷发育成了四面断裂包围的断陷盆地雏形. 卢龙地震的发震构造是一个走滑兼张性的断裂组合， 这样的构造与张家口——渤海地震带的整体活动习性相符， 也反映了张渤带作为一个二级地块的分界截断NNE向的一系列断层所起的作用.      

Study on the earthquake fault of the Lulong <Emphasis Type="Italic">M</Emphasis><Subscript>L</Subscript>=6.2 earthquake by precise relocation of aftershock

We have selected 171 near-field records from 391 aftershock records of the Lulong, Hebei Province, earthquake in October 1982 and relocated the hypocenter of 45 aftershocks using the program Hypoinverse. The distribution of aftershocks reveals a set of earthquake faults: a WNW stretching fault truncates two NNE stretching faults. The two branches of faults show the conjugate structure which is often seen in brittle fracture. The NNE stretching faults are connected together. The Luanhe river valley near Lulong developed to a rudiment rift basin surrounded by a series of faults. The fault of Lulong earthquake is a strike-slip fault with tension component. This fault type matches with the activity of Zhangjiakou-Bohai seismic belt (Zhang-Bo belt) and also shows the action of Zhang-Bo belt as a boundary of two secondary active blocks that truncates the NNE fault.     

Geodynamic framework of large volcanic fields highlighted by SRTM DEMs: Method evaluation and perspectives exampled on three areas from the Cameroon Volcanic Line

This study is a part of a wider investigation to evaluate how much can be learnt by using low-cost methods such as systematic moderate-resolution remote sensing to map and quantify geological structures at the regional scale on very large volcanic provinces only partly studied in the field. Volcanic-centre and cinder-cone distribution, faults and structural lineaments are mapped combining Shuttle Radar Topography Mission (SRTM), Digital Elevation Models (DEMs) and Landsat satellite images. As an example of the method, we present the interpretation of structural data and morphological features of three contrasted areas from the Cameroon Volcanic Line (Tombel graben, Upper Benue valley, and Ngaoundéré area) for which local field studies are available for comparison. At a local scale, this remote-sensing method of mapping displays good to excellent correlations with previously published data and, by itself, it allows one to constrain the structural setting of each area. Numerical treatment of vent and cinder-cone localisation can be related to tension fractures (T direction), whereas numerical treatment of the lineaments constrains the associated fault system to a single transtensional (strike-slip + extension) Riedel type fracture network. The first results on the Cameroon Volcanic Line are promising and could be used at a larger scale on numerous volcanic provinces for which field data are not yet available.     

Study on the earthquake fault of the Lulong M L=6.2 earthquake by precise relocation of aftershock

We have selected 171 near-field records from 391 aftershock records of the Lulong, Hebei Province, earthquake in October 1982 and relocated the hypocenter of 45 aftershocks using the program Hypoinverse. The distribution of aftershocks reveals a set of earthquake faults: a WNW stretching fault truncates two NNE stretching faults. The two branches of faults show the conjugate structure which is often seen in brittle fracture. The NNE stretching faults are connected together. The Luanhe river valley near Lulong developed to a rudiment rift basin surrounded by a series of faults. The fault of Lulong earthquake is a strike-slip fault with tension component. This fault type matches with the activity of Zhangjiakou-Bohai seismic belt (Zhang-Bo belt) and also shows the action of Zhang-Bo belt as a boundary of two secondary active blocks that truncates the NNE fault. Foundation item: National Natural Science Foundation of China (40234038). Contribution No. 05FE3016, Institute of Geophysics, China Earthquake Administration.     

Study on the earthquake fault of the Lulong ML=6.2 earthquake by precise relocation of aftershock

Introduction The Lulong county is about 75 km northeast to Tangshan in Hebei Province. An earthquake of ML=6.2 took place on October 19, 1982 about 4 km northeast to the county town. The epicenter of the mainshock is located at 39°57′N, 119°04′E by the Beijing seismic network. The 1976 Tang- shan 7.8 earthquake and the successive Luanxian 7.1, Ninghe 6.9 and the Lulong earthquake spread in NE-SW direction in space. SONG and WANG et al of Institute of Geophysics, China Seismolog…     

Age of the source of the Jarrafa gravity and magnetic anomalies offshore Libya and its geodynamic implications

The interpretation of the Jarrafa magnetic and gravity highs, NW Libyan offshore, suggests that it may be caused by a body of high-density and high magnetization. Analysis of their power spectra indicates two groups of sources at: (1) 2.7 km depth, probably related to the igneous rocks, some of which were penetrated in the JA-1 borehole, (2) 5 km depth, corresponding to the top of the causative body and (3) 10 km depth, probably referring to the local basement depth. The boundary analysis derived from applied horizontal gradient to both gravity and magnetic data reveals lineaments many of which can be related to geological structures (grabens, horsts and faults).The poor correlation between pseudogravity fields for induced magnetization and observed gravity fields strongly suggests that the causative structure has a remanent magnetization (D = −16°, I = 23°) of Early Cretaceous age, fitting with the opening of the Neo Tethys 3 Ocean.Three-dimensional interpretation techniques indicate that the magnetic source of the Jarrafa magnetic anomaly has a magnetization intensity of 0.46 A/m, which is required to simulate the amplitude of the observed magnetic anomaly. The magnetic model shows that it has a base level at 15 km.The history of the area combined with the analysis and interpretation of the gravity and magnetic data suggests that: (1) the source of the Jarrafa anomaly is a mafic igneous rock and it may have formed during an Early Cretaceous extensional phase and (2) the Jarrafa basin was left-laterally sheared along the WNW Hercynian North Graben Fault Zone, during its reactivation in the Early Cretaceous.     

Using chlorofluorocarbons (CFCs) and tritium (3H) to estimate groundwater age and flow velocity in Hohhot Basin,China

The concentrations of chlorofluorocarbons (CFC‐11, CFC‐12 and CFC‐113) and tritium (³H) content in groundwater were used to date groundwater age, delineate groundwater flow systems and estimate flow velocity in the Hohhot basin. The estimated young groundwater age is fallen in the bracket of 21 ~ 50 a and indicates the presence of two different age profiles and flow systems in the shallow groundwater system. Older age waters occur under the topographically low areas, where the aquifer is double‐layer aquifer system consisting of shallow unconfined‐semi‐confined aquifer and deep confined aquifer. This reflects long flow paths associated with regional flow. Groundwater (range from 21 to 34 years) in the north piedmont and east hilly areas, where the aquifer is a single‐layer aquifer consisting of alluvial fans, are typically younger than those in the low areas. The combination of CFCs dating with hydrogeological information indicates that both local and regional flow systems are present at the basin. The regional groundwater flow mainly flows from the north and east to the southwest, the local groundwater flow system occurs nearby the Hohhot city. The mean regional groundwater flow velocity of the shallow groundwater is estimated about 0.73 km/a. These findings can aid in refining hydrogeological conceptual model of the study area. Copyright © 2012 John Wiley & Sons, Ltd.     

Fault tectonic analysis of Kii peninsula,Southwest Japan: Preliminary approach to Neogene paleostress sequence near the Nankai subduction zone

The southern part of the Outer Zone of Southwest Japan including the Kii peninsula belongs to the tectonic ‘shadow zone’, where fewer conspicuous active faults and less Quaternary sediments develop than in the Nankai subduction zone and Inner Zone of Southwest Japan. In order to study the paleostress sequence of the Kii peninsula, we analyzed fault‐slip data and tension gashes at pilot sites of Early–Middle Miocene forearc sediments and Late Cretaceous accretionary complex. According to the results, six faulting events are reconstructed in sequence: (i) east–west extension (normal faulting); (ii) east–west compression and north–south extension (strike‐slip faulting); (iii) NNW–SSE compression and ENE–WSW extension (strike‐slip faulting); (iv) northeast–southwest compression and northwest–southeast extension (strike‐slip faulting); (v) WNW–ESE compression (strike‐slip or reverse faulting); and (vi) NNE–SSW extension. The north–south to NNW–SSE trending dyke swarm of Middle Miocene age in the Kii peninsula is thought to be related to Event 3, implying that Event 3 was active at least during the Middle Miocene. Because Event 6 is recognized solely at a site, the overall latest faulting event seems to be Event 5. Assuming that the compression results from the motion of the crust or plate, the compression direction of Event 5 is in good accordance with the present‐day WNW crustal velocity vectors of the Kii peninsula. The stress trajectory map of Southeast Korea and Southwest Japan reveals that the current compression directions of the Kii peninsula correspond to the combinatory stress fields of the Himalayan and Philippine Sea tectonic domains.     

A proposed structure–groundwater model: application to chalky media of the Paris Basin

The groundwater flow in a fissured chalky environment at the northern border of the Paris Basin depends on several geological and hydrogeological parameters. Although the studied sector of the basin presents a homogeneous rock type, it is affected by a fracture network. In this type of environment, in which the permeability is low, the groundwater flow displays significant disruption, which is localized in the Fruges region (northern France). The interconnection of the discontinuities (network of fault and/or joints) is reliant on the structural control of groundwater flow through increases in the hydraulic connection between the unsaturated and the saturated zone. The methodology developed herein makes use of microstructural and regional analysis of the fracture patterns, and allowed consideration of the piezometric variations of the chalk aquifer during periods of low and high groundwater levels (April and October 2001) and a diagraphic representation of the estimated physical parameters (electrical resistivity). This enabled us to construct a ‘flow structure’ conceptual model in which we identify two types of faults: tight walls and flow paths that control the piezometric heads and the flow rate. Model validation was carried out on a similar sector. Copyright © 2007 John Wiley & Sons, Ltd.     

Volcanism and mantle–crust evolution: The Etna case

Mount Etna is located in a particular region of convergence of African and Eurasian plates where intense post-collisional tectonics caused considerable uplift. However we present arguments supporting the hypothesis that volcanism and associated seismic activity would result from a local mantle uprise leading to a “horst”, probably linked to a deep-rooted hot spot. It ensued deformation and fracturing of the overlying crust with emission of aphyric tholeiitic basalts directly from their mantle source, and subsequent development of a “deep reservoir” (or complex of intrusions) at the top of a mantle diapir near 30 km depth. This is advocated by the appearance of porphyritic alkaline lavas whose mineral equilibria and differentiation processes are consistent with an 8–10 kbar pressure, and by the development of central volcanoes. The horst itself appears to have begun in the SW sector of the present volcanic area. Its uplift was greater westward, as seen from the trend of the terraces along the Simeto river, and became later obvious toward the SE. These differential movements produced fractures and faults which are to day evident in the southern area of Mt Etna. The growth of the horst then proceeded in a NE direction, following the regional tectonic lines and with a greater intensity along the side facing SE, crossed by the regional NNW–SSE line (Aeolian–Maltese escarpment).The seismicity and ground deformation registered over the last twenty years support the proposed model. Earthquakes are unfrequent in the lower southern and western areas of the volcano, whereas they are numerous and stronger to the north-east, in the summit area above 1600 m a.s.l., and in the eastern sector along the NW–SE faults and fractures. Finally, a digital elevation model recently published reveals the existence of two tectonic domains. The first one is associated with the horst and contains prevalently NE–SW oriented faults, whereas the second is mainly linked to regional tectonics with NNW–SSE and NW–SE faults and fractures.     

New insights in the geodynamics of the Lipari–Vulcano area (Aeolian Archipelago,southern Italy) from geological,geodetic and seismological data

Geological, geodetic and seismological data have been analyzed in order to frame the Lipari–Vulcano complex (Aeolian archipelago, southern Italy) into the geodynamic context of the southeastern Tyrrhenian Sea. It is located at the northern end of a major NNW–SSE trending right-lateral strike-slip fault system named “Aeolian–Tindari–Letojanni” which has been interpreted as a lithospheric discontinuity extending from the Aeolian Islands to the Ionian coast of Sicily and separating two different tectonic domains: a contractional one to the west and an extensional one to the north-east. Structural field data consist of structural measurements performed on well-exposed fault planes and fractures. The mesostructures are mostly represented by NW–SE striking normal faults with a dextral-oblique component of motion. Minor structures are represented by N–S oriented joints and tension gashes widespread over the whole analyzed area and particularly along fumarolized sectors. The analyzed seismological dataset (from 1994 to 2013) is based on earthquakes with magnitude ranging between 1.0 and 4.8. The hypocenter distribution depicts two major alignments corresponding to the NNW–SSE trending Aeolian–Tindari–Letojanni fault system and to the WNW–ESE oriented Sisifo–Alicudi fault system. GPS data analysis displays ∼3.0 mm/yr of active shortening between the two islands, with a maximum shortening rate of about 1.0 × 10⁻¹³ s⁻¹, between La Fossa Caldera and south of Vulcanello. This region is bounded to the north by an area where the maximum values of shear strain rates, of about 0.7 × 10⁻¹³ s⁻¹ are observed. This major change occurs in the area south of Vulcanello that is also characterized by a transition in the way of the vertical axis rotation. Moreover, both the islands show a clear subsidence process, as suggested by negative vertical velocities of all GPS stations which exhibit a decrease from about −15 to −7 mm/yr from north to south. New data suggest that the current kinematics of the Lipari–Vulcano complex can be framed in the tectonic context of the eastward migrating Sisifo–Alicudi fault system. This is dominated by transpressive tectonics in which contractional and minor extensional structures can coexist with strike-slip motion.     

Relationships between tectonic and geomorphological linear features in the Guadix-Baza basin,southern Spain

Linear elements of the landscape of the Guadix-Baza basin, southern Spain, were identified from a Landsat TM image. Three important lineament trends have been identified in the Guadix-Baza basin. The first is NE–SW, which is the dominant trend in the basin; the second is NW–SE, and the third is ENE–WSW. These three trends are correlated to the major faults of the Guadix-Baza basin. The study of linear features by the analysis of satellite data has revealed a strong link between the buried tectonic structures and the morphological features appearing at the surface. The distribution and density of lineaments explains much of the morphology of the land surface. It is possible to reconstruct elements of the tectonic and denudational history of the region and show that during Quaternary times lineaments controlled the sedimentation of the basin and the drainage pattern. Copyright © 1999 John Wiley & Sons, Ltd.     

Delineating coastal groundwater discharge processes in a wetland area by means of electrical resistivity imaging, 224Ra and 222Rn

Coastal groundwater discharge (CGD) plays an important role in coastal hydrogeological systems as they are a water resource that needs to be managed, particularly in wetland areas. Despite its importance, identifying and monitoring CGD often presents physical and logistical constraints, restraining the application of more traditional submarine groundwater discharge surveying techniques. Here we investigate the capability of electrical resistivity imaging (ERI) in the Peníscola wetland (Mediterranean coast, Spain). ERI surveying made it possible to identify and delineate an ascending regional groundwater flow of thermal and Ra‐enriched groundwater converging with local flows and seawater intrusion. The continuous inputs of Ra‐rich groundwater have induced high activities of Ra isotopes and ²²²Rn into the marsh area, becoming among the highest previously reported in wetlands and coastal lagoons. Geoelectrical imaging enabled inferring focused upward discharging areas, leaking from the aquifer roof through a confining unit and culminating as spring pools nourishing the wetland system. Forward modelling over idealized subsurface configurations, borehole datasets, potentiometric records from standpipe piezometers, petrophysical analysis, and four natural and independent tracers (²²⁴Ra, ²²²Rn, temperature and salinity) permitted assessing the geoelectrical model and a derived hydrogeological pattern. The research highlights the potential of ERI to improve hydrogeological characterization of subsurface processes in complex contexts, with different converging flows. Additionally, a hydrogeological conceptual model for a groundwater‐fed coastal wetland was proposed, based on the integration of surveying datasets. Copyright © 2013 John Wiley & Sons, Ltd.     

卫星照片的线性破裂解译

为了研究大地震发生的地质构造背景,卫照分析是很重要的。我们解译了鄂尔多斯周围和华北地区的卫星照片。共解译出巨、大、中、小各类线性破裂4737条,发现它们的最新活动表现在:1.继承性:即新的破裂沿袭中生代以前的老断裂活动;2.新生性:部分破裂在第三纪特别是第四纪形成。两种表现在卫片影象上都相当清楚。我们认为这些由卫照识别出最新活动断裂与地震活动有一定关系。     

3-D HLEM Modeling of Tropical Weathering: A Trial from a Granitic Area of N-W Rajasthan, India

--In a sand-covered granite terrain of northwestern Rajasthan, India, a five-frequency HLEM survey along a 10-km traverse line generated several clear and strong anomalies. Subjected to a joint constrained 1-D layered earth inversion, the IP and OP frequency soundings at each point of observation yields either no solution or one which is inconsistent with the adjacent point. On the other hand, a 3-D model fitting of these anomalies with a tabular body in a layered host leads to a more meaningful interpretation, suggesting the presence of (1) pockets of weathered conductive material and (2) resistive intruding dykes, embedded in a semi-weathered layer, as the cause of the observed anomalies. The locations of weathered pockets are probably determined by pre-existing weak structures such as joints, fractures and faults, which facilitated movement of groundwater and hence weathering. Thus covered features deep in the bedrock such as intrusives, joints, fractures and faults, which are not directly detectable by the HLEM method, being under a more conductive overburden, are indirectly detected through their imprints left in the overlying weathering profile.     

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.     

Recent Crustal Stress Field and Dislocation Along Seismic Faults in the East China Region

INTRODUCTIONThere exist many methods for studying recent crustal stress field.One of the most commonmethodsis to use focal mechanismsolution data of earthquakes to deduce the recent crustal stressfield.The method is simple and feasible and the data obtained is reliable.Yan Jiaquan,et al.(1979)usedthe method to study the recent tectonic stress field in China and its adjacent areas andgave a rough configuration and regional characteristics of the stress field.Li Qinzu(1980),WeiGuangxing,e…