Tectonic Fault System Research Articles

Magnetic field map of the Wilhelm Archipelago shelf zone, West Antarctica

The Antarctic Digital Magnetic Anomaly Project is an international research effort to construct a magnetic map of the continent based on ground, satellite, marine, and aeromagnetic surveys. This paper reports the magnetic mapping of the shelf zone in the SE part of the Wilhelm Archipelago, West Antarctica, based on magnetic surveys conducted with Zodiac boats. A spectacular feature of this area is the strong magnetic anomaly of the Antarctic Peninsula (AP) batholith, which was the product of subduction-related Mesozoic–Cenozoic arc magmatism on the former margin of Western Gondwana. We constructed and analyzed a detailed magnetic map of magnetic field anomalies using field observations of rock exposures on the islands and magnetic properties of rocks from laboratory data. The oldest volcanic rocks of Jurassic to Lower Cretaceous age relate to N-NE trending bands of negative magnetic field. The largest feature in the study area is an Upper Cretaceous/Paleogene granodiorite complex that produces a positive magnetic anomaly. Many smaller anomalies are also present over gabbroid bodies of Cretaceous age. Two-dimensional magnetic modeling shows that heterogeneities in the upper crust may have magnetic susceptibilities in the range of 0.005–0.13 SI. Magnetic field anomalies also delineate an orthogonal system of tectonic faults, including the main NE fault along the Penola Strait (sub-parallel to the AP coastline) and four intersecting faults. These fault systems may be associated with different stages of continental margin evolution along the Antarctic Peninsula.

Influence of facies and tectonic structure on the reservoir properties distribution

The lithofacies features influence of productive strata and a system of tectonic faults on the reservoir properties distribution of Jurassic deposits one of the area of Western Siberia was analysed. Main productive strata in this place is Tyumen suite. The facies model of field was updated according reconstruction of sedimentation environment by electrometric facies models (by Muromcev V. S), interpretation results of seismic and core descrition. Dedicated sedimentation zones show main conception of Western Siberia basin evolution in Jurassic. Lithofacies analysis allow to identify main features of sedimentation zones, find out a reasons of uneven reservoir properties distribution. Also influence of tectonic faults system on reservoir properties of productive layers was found. Data summation help update fault model and highlight new low-amplitude faults. Next comparing maps of initial and remaining recoverable reserves of oil with lithofacies and fault model of reservoir rock help identify reason of zones with high density deposits forming and develop most effictient stimulation of oil recovery.

Constraints on fracture distribution in the Los Humeros geothermal field from beamforming of ambient seismic noise

Abstract. Faults and fractures are crucial parameters for geothermal systems as they provide secondary permeability allowing fluids to circulate and heat up in the subsurface. In this study, we use an ambient seismic noise technique referred to as three-component (3C) beamforming to detect and characterize faults and fractures at a geothermal field in Mexico. We perform 3C beamforming on ambient noise data collected at the Los Humeros Geothermal Field (LHGF) in Mexico. The LHGF is situated in a complicated geological area, part of a volcanic complex with an active tectonic fault system. Although the LHGF has been exploited for geothermal resources for over 3 decades, the field has yet to be explored at depths greater than 3 km. Consequently, it is currently unknown how deep faults and fractures permeate, and the LHGF has yet to be exploited to its full capacity. Three-component beamforming extracts the polarizations, azimuths and phase velocities of coherent waves as a function of frequency, providing a detailed characterization of the seismic wavefield. In this study, 3C beamforming of ambient seismic noise is used to determine surface wave velocities as a function of depth and propagation direction. Anisotropic velocities are assumed to relate to the presence of faults giving an indication of the maximum depth of permeability, a vital parameter for fluid circulation and heat flow throughout a geothermal field. Three-component beamforming was used to determine if the complex surface fracture system permeates deeper than is currently known. Our results show that anisotropy of seismic velocities does not decline significantly with depth, suggesting that faults and fractures, and hence permeability, persist below 3 km. Moreover, estimates of fast and slow directions, with respect to surface wave velocities, are used to determine the orientation of faults with depth. The north-east (NE) and north–north-west (NNW) orientation of the fast direction corresponds to the orientation of the Arroyo Grande and Maxtaloya–Los Humeros Fault swarms, respectively. NE and NNW orientations of anisotropy align with other major faults within the LHGF at depths permeating to 6 km.

Implications of slow fault slip for hydraulic-fracturing-induced seismicity

Since the discovery of slow-slip phenomena, scientific understanding of the behavior of active fault systems has been transformed significantly. It is now recognized that tectonic fault systems are characterized by a spectrum of slip behavior, from “regular” (stick-slip) earthquakes that radiate elastic wave energy and occur on a timescale of seconds, to slow-slip events with durations ranging from minutes to years. More recently, slow-slip phenomena have been observed and modeled in association with injection-induced seismicity. This includes evidence for predominantly slow fault slip during injection that triggered dynamic rupture elsewhere on a fault. In the case of hydraulic fracturing, slow-slip behavior is consistent with the frictional characteristics of faults in clay-rich rocks. A change in pore pressure or slip rate can cause a fault to transition from slow to unstable slip. Through real-time monitoring of slip-slip processes and, potentially, the development of operational adjustments to reduce the hazard of damaging ground motions, a better understanding of slow-slip processes could contribute to improved risk mitigation for induced earthquakes. Effective tools for direct observation of slow-slip processes include tiltmeters, strainmeters, global navigation satellite systems, interferometric synthetic aperture radar, and distributed fiber-optic sensing.

3D Active Source Seismic Imaging of the Alpine Fault Zone and the Whataroa Glacial Valley in New Zealand

AbstractThe Alpine Fault zone in New Zealand marks a major transpressional plate boundary that is late in its typical earthquake cycle. Understanding the subsurface structures is crucial to understand the tectonic processes taking place. A unique seismic survey including 2D lines, a 3D array, and borehole recordings, has been performed in the Whataroa Valley and provides new insights into the Alpine Fault zone down to ∼2 km depth at the location of the Deep Fault Drilling Project (DFDP)‐2 drill site. Seismic images are obtained by focusing prestack depth migration approaches. Despite the challenging conditions for seismic imaging within a sediment filled glacial valley and steeply dipping valley flanks, several structures related to the valley itself as well as the tectonic fault system are imaged. A set of several reflectors dipping 40°–56° to the southeast are identified in a ∼600 m wide zone that is interpreted to be the minimum extent of the damage zone. Different approaches image one distinct reflector dipping at ∼40°, which is interpreted to be the main Alpine Fault reflector located only ∼100 m beneath the maximum drilled depth of the DFDP‐2B borehole. At shallower depths (z < 0.5 km), additional reflectors are identified as fault segments with generally steeper dips up to 56°. Additionally, a glacially over‐deepened trough with nearly horizontally layered sediments and a major fault (z < 0.5 km) are identified 0.5–1 km south of the DFDP‐2B borehole. Thus, a complex structural environment is seismically imaged and shows the complexity of the Alpine Fault at Whataroa.

A study on the relationship between gas-geochemical field and tectonic fault activities in the rivermouth area of northwestern Gulf of Tonkin

The article mentions the results of the new analysis of gas-geochemical and high resolution shallow seismic data acquired by the sea surveys in 2016, which revealed a remarkable coincidence between the seabed gas anomalies at river mouth area of Gulf of Tonkin and the gas distortion/accumulation phenomena in the near-surface sediment layers, especially right above the large tectonic fault systems, such as Red river, Lo river and Chay river. The gas-geochemical analysis reveals the existences of thermogenic and metamorphic methane and carbon dioxide gases within the faults of Red river and on Cat Ba island, anomalies of helium and hydrogen as well as the “heavy” isotopic carbon signals of methane and carbon dioxide in the areas of near-surface active faults. These new results suggest the initial conclusions about the relationship between gas-geochemical field and tectonic fault activities in study area.

Unraveling the geologic and tectonic history of the Memnonia-Sirenum region of Mars: Implications on the early formation of the Tharsis rise

The geologic and tectonic history of the Memnonia-Sirenum region of Mars has been reconstructed on the basis of geologic mapping and relative-age dating of rock units and structures using crater counts and superposition relations. Comparisons between the ages of rock unit formation and the orientations of the earliest structures associated with Tharsis demonstrate a strong interplay among tectonic, magmatic, and aqueous activity in the Memnonia-Sirenum region. Early Noachian geologic activity identified within this region includes the formation of large northeast-trending, extensional basins. Stratigraphic and tectonic evidence suggests that these basins formed concurrently with the early formation of Tharsis when the dynamo and associated magnetosphere were still in operation. In addition to the ancient basins, later Tharsis-influenced activity includes prominent tectonic fault systems associated with the formation of Tharsis and Arsia Mons. Detailed mapping of the faults indicates that structures associated with Memnonia and Sirenum Fossae resulted from the formation of Tharsis during the Middle to Late Noachian. Late-stage (Amazonian) activity also identified within this region includes valley networks and collapse depressions that are linked and/or occur among Tharsis-centered faults that cut features throughout this region, including Mangala Valles.

Numerical Modeling of the Stress–Strain State and Results of GPS Monitoring of the Epicentral Area of the August 24, 2014 Earthquake (Napa, California, USA)

This paper reports the results of numerical modeling of the stress–strain state of the epicentral area before and after the August 24, 2014 earthquake in Napa, California, USA, compared to calculated data obtained in instrumental studies in the dilatation areas based on GPS observation results. Numerical modeling has made it possible to calculate the stress–strain state of the epicentral area affected by the tectonic fault system. GPS observation data on the epicentral area of the earthquake and the results of numerical modeling of the stress–strain state before and after the considered earthquake have been analyzed. A trend toward localization of earthquake epicenters in the region of high stress intensity concentration has been confirmed. It has been proved that aftershock development is due to the drop in stress caused by a new fracture and that the aftershock cluster that occurred was localized in the area of decreased stress intensity.

Mineralogical features of the clastic dykes of the Eastern Carpathians Skybova zone

We determined several areas with outcrops of clastic dikes which occur in the rocks of the Menilite suite of the Upper Paleogene period in the so-called Skybova zone [Ukr. Ски́ бова зо́на – the largest tectonic zone within the Carpathian folded structure. The word “skyba” derived from Polish, and is used in relation to nappe – Translator`s Note ] of the Eastern Carpathians. The objective of this article is to reveal the peculiarities of bedding, mineralogical composition and structural-texture peculiarities of the clastic dikes of the Sukyl, Stryi and Skhidnytsia river basins. During our research, we used the method of field structural-geological surveys, traditional method of laboratory analysis of mineralogical-petrographic composition of rocks in thin sections. As a result, we studied the conditions of bedding of clastic dikes, mineral composition and structural-texture peculiarities. We determined that the dikes are represented by aleuro-sandstone and aleurolite with quartz-carbonate cement. Aleurolite most often represents pre-selvage parts of dikes. Mineral grains are mostly formed by quartz of different degrees of roundness. In the selvages of the studied dikes, we observed a decrease in the sizes of mineral grains, enrichment of these parts of dikes by organic compound, increase in the content of carbonate minerals in the rock cement and numerous microdeformations of mineral grains. Also we determined an insignificant content of ore minerals in some studied plots. Additional analysis conducted for a polished sample which characterizes the vertical section of dike in the area of the river Sukyl allowed us to determine the structural signs in its selvages, indicating injection character of dikes` upward introduction to the bearing rocks. We studied the microdeformation of dikes` mineral grains, which are represented by veinles, microfaults and microshifts withclear mixing of their fragments. The obtained results indicate the formation of clastic dikes of the Skybova zone of the Eastern Carpathians in conditions of compression, when relatively flexible material of selvages of the dikes, represented by carbonates and organic compound, contributed to the introduction of the latter to the layer of flysch through the system of tectonic faults of north-west stretch.

Technogenic tectonic seismicity in Kuzbass

This paper presents an analysis of the development of the current seismic state of the Kuznetsk coal basin, which is characterized by an increase in technogenic seismicity of different types under the influence of prolonged intensive mining operations. The development of technogenesis led to a significant increase in technogenic seismicity in the Kuznetsk Basin in the 1970-1980s, when the number of technogenic earthquakes began to exceed the number of natural earthquakes. Among the various types of induced seismicity, special attention is paid to strong technogenic tectonic earthquakes with a regional magnitude Mb ≥ 3 and, accordingly, a seismic energy release of more than 109 J, i.e., earthquakes of energy class K > 9. These small-focus earthquakes are often accompanied by destruction of underground mines, collapse of quarries and pits, damage to surface facilities and equipment, and other adverse effects. In this paper, such earthquakes are defined as technogenic tectonic to emphasize their dual origin: technogenic impacts and the subsequent relaxation of tectonic stresses. It is also noted that the Earth’s interior in Kuzbass initially had its own natural seismicity and a developed system of tectonic faults. Natural seismotectonic activity combined with constantly increasing scales of mining and explosive consumption has led to an increase in the number of technogenic seismic events and their intensity. A striking example of such an event was the 18 June, 2013 Bachat earthquake with a regional magnitude Mb= 5.8 and a seismic intensity of 7 in the epicentral zone. It was the world’s largest man-made earthquake induced by the mining of solid minerals. We consider the possible causes of this catastrophic earthquake and discuss the conditions favoring the formation of foci of such technogenic tectonic earthquakes resulting from changes in the geodynamic and hydrogeological conditions in the Earth’s crust under man-caused impacts. These induced changes in natural processes are accompanied by a change in the stress-strain state, resulting in the concentration of tectonic stresses at heterogeneities and in fault zones, which become sources of induced technogenic seismicity.The paper discusses the current period of the occurrence and increase in such anthropogenic seismicity in the Kuzbass region with increasing scales of coal mining and blasting. Over the last 20 years, the consumption of explosives at Kuzbass enterprises increased from 100-200 to 500-600 thousand tons per year, and, accordingly, the amounts of broken and transported rock increased from several million tons per year to a billion tons per year, which disturbed the dynamic equilibrium in the Earth’s crust and changed the existing field of tectonic stresses. Moreover, the continuously increasing consumption of explosives has also increased the technogenic impact on the crust structures. The location of the epicenters of large-scale blasts inducing seismic events with regional magnitudes Mb= 3.0-4.5 has made it possible to identify regions with the greatest technogenic impact in Kuzbass. Using the data of the ISC seismological catalog, we separated seismic events with the above magnitudes into day and night ones. Since blasting work is forbidden at night, night seismic events are referred to as technogenic tectonic earthquakes (night event criterion). The maximum magnitude of seismic events induced by blasting operations in the Kuznetsk Basin was estimated at Mb ≤ 4.4. The annual number of technogenic tectonic earthquakes with 3.0 ≤ Mb ≤ 3.4, 3.5 ≤ Mb ≤ 3.9, 4.0 ≤ Mb ≤ 4.4, and Mb ≥ 4.5 was determined based on the night event criterion. The regions of their occurrence were identified from the location of the epicenters of technogenic tectonic earthquakes.

Modeling of the stress-strain state in the earthquake epicenter area (Kumamoto Earthquake, Japan), 16.04.2016 M 7.3

On the 16th of April, 2016, a strong earthquake with M 7,3 occurred in the Kumamoto prefecture (Kyushu, Japan). This earthquake is the strongest in the last 30 years in this area. For a day before the main shock, two foreshocks with M 6,4 were registered. For seven days after the main shock, aftershocks activity spread to the north-east and south-west, most of the hypocentres of the aftershocks with M 6,4 were localized within the seismogenic layer in the depth interval from 5 to 10 km. The authors have modeled a stress-strain state (SSS) of the epicentral area be fore the earthquake and after it (after the formation of the main fault). For this purpose, a software package is used, that allows 2-D formulation (plane strain condition), for modeling SSS block heterogeneous geological environment, disrupted by a system of tectonic faults. The faults are modeled in the form of extended zones of the dispersed geomaterial, which elastic modulus are significantly lower than the elastic modulus of the environmental media. A structural-tectonic scheme of the Kumamoto earthquake area is used. An analysis of the results of SSS modeling has been done for the area 30x40 km before and after the earthquake. It is shown that the area and magnitude of the stress intensity in anomalous zones are the predictive signs of the location and intensity of a possible strong crustal earthquake, and the vector of the rapid decrease in the potential energy of deformation could be a guide for the most probable direction of tectonic rupture during a crustal earthquake. The results received can be useful in a deterministic approach to seismic hazard assessment and carrying out the geophysical observations focused on the forecast of the strong crustal earthquakes in the continental areas.

Measuring earthquake source parameters in the Mendocino triple junction region using a dense OBS array: Implications for fault strength variations

Subduction zones produce earthquakes on a set of faults that operate under a wide variety of conditions resulting from considerable variations in depth, temperature, rock type, and fluid pressure. These variations likely lead to variation in the stress levels that drives particular earthquakes and that in turn effects the magnitude of seismic shaking they produce. In the Mendocino Triple Junction (MTJ) region, intraplate faults within the mantle of the subducting plate fail regularly in energetic earthquakes while the adjacent thrust interface of the Cascadia subduction zone remains seismically quiet despite the likelihood that it operates at much lower levels of stress and strength. In 2012, as part of the Cascadia Initiative community experiment, an ocean bottom seismometer (OBS) array was deployed in the MTJ area, providing unusually dense data covering both the inter- and intra-plate earthquakes. Combining these data with onshore networks, we detect and relocate 1137 earthquakes with a three dimensional velocity model. We perform detailed spectral and time domain analysis to study variations in earthquake source properties between the different types of faults. We observe a wide variability of stress drops and systematic lateral and depth variations in the earthquake source spectra resulting from the different types of tectonic fault systems in this region: intraplate faults within the subducted oceanic mantle, the Mendocino transform plate boundary fault, and the thrust interface of the Cascadia subduction zone. Some of the depth variability of source spectra can be explained by the expected increase in rupture velocity with depth. However, the overall variation in stress drop estimates is consistent with the highest stress drop earthquakes occurring in the depth range predicted by strength envelopes. Moreover, the earthquakes in the vicinity of the thrust interface, likely including some within the subducted oceanic crust, show clearly lower stress drops and depletion of high-frequency radiation for their size compared to events in the oceanic mantle and along the transform fault at a given depth. Our results suggest that the variability in earthquake source spectra that can be expected in the Cascadia subduction zone is systematic and that the thrust interface operates at a lower stress level than the core of the subducted plate a few kilometers away.

Periodic Vesicle Formation in Tectonic Fault Zones--an Ideal Scenario for Molecular Evolution.

Tectonic fault systems in the continental crust offer huge networks of interconnected channels and cavities. Filled mainly with water and carbon dioxide (CO2), containing a wide variety of hydrothermal chemistry and numerous catalytic surfaces, they may offer ideal reaction conditions for prebiotic chemistry. In these systems, an accumulation zone for organic compounds will develop at a depth of approximately 1 km where CO2 turns sub-critical and dissolved components precipitate. At this point, periodic pressure changes caused for example by tidal influences or geyser activity may generate a cyclic process involving repeated phase transitions of carbon dioxide. In the presence of amphiphilic compounds, this will necessarily lead to the transient formation of coated water droplets in the gas phase and corresponding vesicular structures in the aqueous environment. During this process, the concentration of organic components inside the droplets and vesicles would be drastically increased, allowing for favorable reaction conditions and, in case of the vesicles generated, large trans-membrane concentration gradients. Altogether, the process of periodic formation and destruction of vesicles could offer a perfect environment for molecular evolution in small compartments and for the generation of protocells. The basic process of vesicle formation is reproduced experimentally with a lipid in a water/CO2 system.

Age determination of linear surface features using the Buffered Crater Counting approach – Case studies of the Sirenum and Fortuna Fossae graben systems on Mars

Buffered Crater Counting (BCC) offers a possibility to determine ages of linear/curvilinear surface features that provide no or only very limited surface areas for the conventional crater counting approach. In this study we applied the BCC analysis to two tectonic fault systems, Fortuna Fossae and a subsection of Sirenum Fossae. We compared BCC results with age estimates derived from conventional crater counting on the surrounding geologic units and investigated to what extent crater ejecta blankets can be used for determining the stratigraphic placement of craters pre- or post-dating the formation of linear features. Furthermore, we introduce a new functionality of the CraterTools software for ArcGIS which allows for a user-friendly semi-automatic application of the otherwise time-consuming procedure of BCC analysis. The software provides the resulting crater size-frequency data in a standard format, which can be read and analyzed in the CraterStats analysis software.Our case studies showed that the BCC approach provides equivalent or even more precise age results compared to the conventional stratigraphic approach. Here, we found that the investigated section of Sirenum Fossae is younger than previously thought. The derived formation age from the BCC analysis is 3.44-0.25+0.1Ga which corresponds to Late instead of Early Hesperian. Fortuna Fossae formed shortly after the emplacement of its now-fractured geologic host unit (Late Hesperian). Ages derived from BCC analysis vary between 3.53-0.11+0.06Ga and 3.50-0.11+0.07Ga. Furthermore, we recommend the use of crater ejecta blankets to position them in the stratigraphic sequence in order to improve crater statistics. However, the accuracy of the results depends on the extent and preservation state of the continuous ejecta blankets in the region of interest. Thus, the applied buffer width has to be chosen carefully according to investigated crater sizes and local observations.

Experimental study of the interplay between magmatic rift intrusion and flank instability with application to the 2001 Mount Etna eruption

AbstractMount Etna volcano is subject to transient magmatic intrusions and flank movement. The east flank of the edifice, in particular, is moving eastward and is dissected by the Timpe Fault System. The relationship of this eastward motion with intrusions and tectonic fault motion, however, remains poorly constrained. Here we explore this relationship by using analogue experiments that are designed to simulate magmatic rift intrusion, flank movement, and fault activity before, during, and after a magmatic intrusion episode. Using particle image velocimetry allows for a precise temporal and spatial analysis of the development and activity of fault systems. The results show that the occurrence of rift intrusion episodes has a direct effect on fault activity. In such a situation, fault activity may occur or may be hindered, depending on the interplay of fault displacement and flank acceleration in response to dike intrusion. Our results demonstrate that a complex interplay may exist between an active tectonic fault system and magmatically induced flank instability. Episodes of magmatic intrusion change the intensity pattern of horizontal flank displacements and may hinder or activate associated faults. We further compare our results with the GPS data of the Mount Etna 2001 eruption and intrusion. We find that syneruptive displacement rates at the Timpe Fault System have differed from the preeruptive or posteruptive periods, which shows a good agreement of both the experimental and the GPS data. Therefore, understanding the flank instability and flank stability at Mount Etna requires consideration of both tectonic and magmatic forcing.

Active tectonics in Quito, Ecuador, assessed by geomorphological studies, GPS data, and crustal seismicity

AbstractThe Quito Fault System (QFS) extends over 60 km along the Interandean Depression in northern Ecuador. Multidisciplinary studies support an interpretation in which two major contemporaneous fault systems affect Quaternary volcanoclastic deposits. Hanging paleovalleys and disruption of drainage networks attest to ongoing crustal deformation and uplift in this region, further confirmed by 15 years of GPS measurements and seismicity. The resulting new kinematic model emphasizes the role of the N‐S segmented, en echelon eastward migrating Quito Fault System (QFS). Northeast of this major tectonic feature, the strike‐slip Guayllabamba Fault System (GFS) aids the eastward transfer of the regional strain toward Colombia. These two tectonic fault systems are active, and the local focal mechanisms are consistent with the direction of relative GPS velocities and the regional stress tensor. Among active features, inherited N‐S direction sutures appear to play a role in confining the active deformation in the Interandean Depression. The most frontal of the Quito faults formed at the tip of a blind thrust, dipping 40°W, is most probably connected at depth to inactive suture to the west. A new GPS data set indicates active shortening rates for Quito blind thrust of up to 4 mm/yr, which decreases northward along the fold system as it connects to the strike‐slip Guayllabamba Fault System. The proximity of these structures to the densely populated Quito region highlights the need for additional tectonic studies in these regions of Ecuador to generate further hazard assessments.

GeoBioScience: Red Wood Ants as Bioindicators for Active Tectonic Fault Systems in the West Eifel (Germany).

Simple SummaryIn a 1.140 km² study area of the volcanic West Eifel, approx. 3,000 Red Wood Ant (RWA; Formica rufa-group) mounds had been identified and correlated with tectonically active gas-permeable faults, mostly strike-slip faults. Linear alignment of RWA mounds and soil gas anomalies distinctly indicate the course of these faults, while clusters of mounds indicate crosscut zones of fault systems, which can be correlated with voids caused by crustal block rotation. This demonstrates that RWA are bioindicators for identifying active fault systems and useful where information on the active regime is incomplete or the resolution by technical means is insufficient.In a 1.140 km² study area of the volcanic West Eifel, a comprehensive investigation established the correlation between red wood ant mound (RWA; Formica rufa-group) sites and active tectonic faults. The current stress field with a NW-SE-trending main stress direction opens pathways for geogenic gases and potential magmas following the same orientation. At the same time, Variscan and Mesozoic fault zones are reactivated. The results showed linear alignments and clusters of approx. 3,000 RWA mounds. While linear mound distribution correlate with strike-slip fault systems documented by quartz and ore veins and fault planes with slickensides, the clusters represent crosscut zones of dominant fault systems. Latter can be correlated with voids caused by crustal block rotation. Gas analyses from soil air, mineral springs and mofettes (CO2, Helium, Radon and H2S) reveal limiting concentrations for the spatial distribution of mounds and colonization. Striking is further the almost complete absence of RWA mounds in the core area of the Quaternary volcanic field. A possible cause can be found in occasionally occurring H2S in the fault systems, which is toxic at miniscule concentrations to the ants. Viewed overall, there is a strong relationship between RWA mounds and active tectonics in the West Eifel.

The role of geophysical and seismological data in evaluating the subsurface structures and tectonic trends of Nile Delta, Egypt

In the present study, the Bouguer, aeromagnetic, and seismological data analysis for Nile Delta including the Greater Cairo region and its surroundings was used to examine and trace the tectonic framework for some deep-seated faults (mostly normal faults with a small strike–slip component) and their orientation, on which most earthquakes have occurred. The new tilt derivative (TDR) geophysical map and Euler deconvolution presented here can be used to trace the structural relationships and their depth investigations across the entire region. Generally, most of the Euler deconvolution results especially from the gravity map were well coincided with the location of contacts derived by TDR particularly NNW to NS, EW, and NE trended structures. The depths to the gravity or magnetic sources, and the locations of the contacts of density contrast were estimated. Results of the Euler deconvolution method suggested that, in the southeastern part of the area, the basement could be observed to be shallow and has become deeper beneath the northern part. Furthermore, the resulting structural map of this study is well correlated with previous geological and seismological data analyses. At least two sets of predominant faults are suspected, faults with a NNW strike (Clysmic trend) which are particularly felt in the southern portion of the Delta, and some of them give it the shape of a “graben like structure.” Another parallel set of faults, having NE–SW strike (Pelusium trend), was also obvious in the southern part between Cairo and Suez cities (at Abu Zabal area). The evaluated trending faults (NNW–SSE or NE–SW) are intersecting with predominant major WNW–ESE to E–W (Tethys trend) striking faults. These intersections may generate more additional seismic pulses and consequently increase the seismic activity for these structures. However, minor NW (Najd Fault System) is obvious in the TDR magnetic map, whereas less attendance NS (East African trend) structural trends are evident in the TDR gravity map. Moreover, it could be said that the southeastern portion of the Nile Delta (especially the eastern portion of Greater Cairo) is affected by highly tectonic fault systems. Finally, a new tectonic map was also evaluated from the resulting structural map, which helps to quantify different structural patterns (faults and/or contacts), and their relations with the regional tectonic trends are discussed.

Hypothesis: origin of life in deep-reaching tectonic faults.

The worldwide discussion on the origin of life encounters difficulties when it comes to estimate the conditions of the early earth and to define plausible environments for the development of the first complex organic molecules. Until now, the role of the earth's crust has been more or less ignored. In our opinion, deep-reaching open, interconnected tectonic fault systems may provide possible reaction habitats ranging from nano- to centimetre and even larger dimensions for the formation of prebiotic molecules. In addition to the presence of all necessary raw materials including phosphate, as well as variable pressure and temperature conditions, we suggest that supercritical CO2 as a nonpolar solvent could have played an important role. A hypothetical model for the origin of life is proposed which will be used to design crucial experiments for the model's verification. Because all proposed processes could still occur in tectonic faults at the present time, it may be possible to detect and analyse the formation of prebiotic molecules in order to assess the validity of the proposed hypothesis.

The structure of the Vladikavkaz Fault Zone based on the study utilizing a complex of geological-geophysical methods

The Vladikavkaz Fault Zone is a regional boundary between the Alpine folded-block system of the Greater Caucasus and Pre-Caucasus foredeep (Ossetian Depression). A complex of geological and geomorphological techniques was used for its study. The data of recent activity of discontinuous and folded dislocations were obtained as a result. Additional application of the microseismic sounding method allowed us to trace the behavior at depth and along the direction of the Vladikavkaz Fault Zone’s branches known on the Earth’s surface from geological and geophysical surveys. An idea of the three-dimensional structure of this system of tectonic faults was made up. It was shown that the structure of the upper section of the fault zone has a form of listric foldthrust, and in the deep layers of the Earth’s crust it is represented by a well-formed contrast zone with subvertical plunging. Expressive deformations of young sediments and a clear manifestation of the fault zone at a depth make it possible to consider the Vladikavkaz Fault as a major seismogenerating structure.