Delineation of groundwater protection zones by the backward particle tracking method: theoretical background and GIS-based stochastic analysis

The backward particle tracking method, an effective and powerful tool that can be used to delineate groundwater protection zones, is presented. The theoretical background and insights on the applicability of this method are provided. Moreover, the present work enriches the backward particle tracking method with an uncertainty analysis concerning the porosity values, applying a Monte Carlo (MC) approach, coupled with the use of geographical information systems (GIS). As an application example, a wellfield in the Komotini area, Greece, is investigated. The present study may serve as a potential guideline for wellfield delineation, particularly in areas like Greece where lack of data related to the hydrogeological system is often a problem.     

The Lemnos 8 January 2013 (M w = 5.7) earthquake: fault slip,aftershock properties and static stress transfer modeling in the north Aegean Sea

We investigate mainshock slip distribution and aftershock activity of the 8 January 2013 M _w?=?5.7 Lemnos earthquake, north Aegean Sea. We analyse the seismic waveforms to better understand the spatio-temporal characteristics of earthquake rupture within the seismogenic layer of the crust. Peak slip values range from 50 to 64 cm and mean slip values range from 10 to 12 cm. The slip patches of the event extend over an area of dimensions 16?×?16 km². We also relocate aftershock catalog locations to image seismic fault dimensions and test earthquake transfer models. The relocated events allowed us to identify the active faults in this area of the north Aegean Sea by locating two, NE–SW linear patterns of aftershocks. The aftershock distribution of the mainshock event clearly reveals a NE–SW striking fault about 40 km offshore Lemnos Island that extends from 2 km up to a depth of 14 km. After the mainshock most of the seismic activity migrated to the east and to the north of the hypocenter due to (a) rupture directivity towards the NE and (b) Coulomb stress transfer. A stress inversion analysis based on 14 focal mechanisms of aftershocks showed that the maximum horizontal stress is compressional at N84°E. The static stress transfer analysis for all post-1943 major events in the North Aegean shows no evidence for triggering of the 2013 event. We suggest that the 2013 event occurred due to tectonic loading of the North Aegean crust.     

Hypercube-Based Visualization Architecture for Web-Based Environmental Geospatial Information Systems

The geospatial field significantly influences the development of the environmental domain, including a wide range of geospatial and cartographic information systems, such as Geographic Information Systems (GIS), Multimedia Atlas Information Systems (MAIS) and more recently web-based GIS (Web-GIS). In this context, we introduce web-based environmental geospatial information systems (Web-EGIS) as a special case of Web-GIS, aiming to integrate the functionalities of geospatial information systems with the enormous quantity of specialized, distributed and highly heterogeneous environmental geo-referenced data and services. We define three main characteristics of the Web-EGIS. The first is a generic hypercube-based data organization and visualization. The next characteristic is a standard-based, three-tier service-oriented architecture. The third and last characteristic is the traceability of the architectural and design decisions, for which we introduce the new concept of an ‘Environmental Application Context’, arguing that not only the functional but also the non-functional requirements (NFRs) have an important role in defining the architecture, software components and data services of such systems. In a nutshell, a Web-EGIS is characterized by a coherent user experience through the hypercube-based visualization concept, technically supported by a service-oriented architecture that is structured according to an extensive analysis of NFRs. On this basis, we introduce the Geodata visualization and interactive training environment (GeoVITe) Platform for Interdisciplinary Environmental Research as a reference implementation of a Web-EGIS with its basic design requirements, integrative hypercube-based visualization for heterogeneous data sources, extended web cartography functionalities, and its de facto system architecture. The concept of the hypercube-based visualization is better transferred to the system architecture by understanding the ‘Environmental Application Context’ of this particular Web-EGIS, which also makes it easier to maintain and enhance. The resulting system is a support platform for research activities in the environmental domain.     

Earthquake generation in Cyprus revealed by the evolving stress field

Strong earthquake occurrence (M ≥ 6.0) onshore and offshore the Cyprus Island constitutes significant seismic hazard because they occur close to populated areas. Seismicity is weak south of the Island along the Cyprean Arc and strong events are aligned along the Paphos transform fault and Larnaka thrust fault zone that were already known and the Lemessos thrust fault zone that defined in the present study. By combining the past history of strong (M ≥ 6.0) events and the long-term tectonic loading on these major fault zones, the evolution of the stress field from 1896 until the present is derived. Although uncertainties exist in the location, magnitude and fault geometries of the early earthquakes included in our stress evolutionary model, the resulting stress field provides an explanation of later earthquake triggering. It was evidenced that the locations of all the strong events were preceded by a static stress change that encouraged failure. The current state of the evolved stress field may provide evidence for the future seismic hazard. Areas of positive static stress changes were identified in the southwestern offshore area that can be considered as possible sites of future seismic activity.     

Ein stratiformes Fluoritvorkommen im Zechsteindolomit bei Eschwege und Sontra in Hessen

Zusammenfassung Im Hauptdolomit (Ca₂) und im Plattendolomit (Ca₃) des mittleren Zechsteins bei Eschwege und Sontra in Hessen wurde 1974 erstmals Fluorit entdeckt. Durch Bohrungen, chemische und geochemische Untersuchungen konnte nachgewiesen werden, daß im Hauptdolomit der Fluorit schichtgebunden, gelegentlich in dunklen Lagen und Linsen bis 0,5 m mächtig, makroskopisch sichtbar auftritt. Häufiger kommt er in 18–20 m mächtigen Zonen vor, die aber wegen des geringen Fluoritgehaltes von unter 10 % CaF₂ sich von dem grauweißen Dolomit ohne Fluorit nicht unterscheiden.In den dunklen bis schwarz gefärbten Lagen schwanken die Fluoritgehalte zwischen 10 und 50 % CaF₂. Einzelproben enthalten bis 80 % CaF₂. Die Dunkelfärbung ist teils durch den Gehalt von violettem Fluorit, mehr noch durch Bitumen bedingt.Fluorit wurde ferner im stratigraphisch höher gelegenen Plattendolomit (Ca₃) der Leine-Serie Z3 gefunden. In Aufschlüssen und Steinbrüchen in der Nähe von Sontra enthält der Plattendolomit lokal 1–4 % CaF₂.Die makro- und mikroskopisch sichtbare Wechsellagerung von Fluorit und Dolomit mit einem deutlichen Lagengefüge und das Fehlen von hydrothermalem Fluorit und anderen Mineralien auf Gängen und Klüften sind Beweise für eine synsedimentäre Bildung des Fluorites im Hauptdolomit (Ca₂) und Plattendolomit (Ca₃) in Hessen. Für den Hauptdolomit wird angenommen, daß er spätdiagenetisch entstanden ist. Dies dürfte auch für den Fluorit zutreffen. Als Bildungsbereich werden flache Lagunen mit salinärer Fazies angenommen. Das Fluor stammt aus dem normalen Gehalt des Meerwassers. Es muß aber angenommen werden, daß der Fluorgehalt des Meerwassers durch Zufuhr von Fluor aus dem Festlande, z. B. aus den fluorreichen Graniten des Harzes merklich erhöht wurde. Nur so sind die großen Fluoritmengen im Zechsteindolomit in Hessen zu erklären. Sie werden auf 5–7·10⁶ + CaF₂ geschätzt.

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In 1974, fluorite was detected for the first time in the Hauptdolomit (Ca₂) and in the Plattendolomit (Ca₃) of the Middle Zechsteinformation near Eschwege and Sontra, Hessia. It was confirmed by means of drilling, chemical and geochemical investigations that the fluorite in the Hauptdolomit is stratabound. It occurs both locally in the form of macroscopic dark layers and lenses of up to 0,5 m thickness and moreoften, as zones up to 18–20 m thick which cannot macroscopically be distinguished from the greyish white dolomite without fluorite because of the low CaF₂ content (less than 10 %).The fluorite contents vary between 10 an 50 % CaF₂ in the dark black layers. Special samples may contain up to 80 % CaF₂. The dark colour derives partly from the lilac fluorite but to a greater degree from bitumous material.Fluorite has also been detected in the stratigraphically higher Plattendolomit (Ca₃) of the Leine-Series Z 3. Outcrops and quarries near Sontra have local contents of 1–4 % CaF₂.The macroscopic and microscopic interstratification of fluorite and dolomite with clear layer textures and the absence of hydrothermal fluorite and other minerals in veins of fissures are evidence for a synsedimentary formation of the fluorite in the Hauptdolomit (Ca₂) and the Plattendolomit (Ca₃). The Hauptdolomit is thought to have developed during late diagenesis. This should be valid for the fluorite, too. Shallow lagoons of a salinar facies are thought to have been the depositional environment. The fluorite precipitated from the sea waters, which were apparently enriched in fluorine by erosion at the fluorine rich granites of the Harz mountains. This is the only obvious explanation of the large amounts of fluorine in the Zechstein dolomite, estimated at 5–7×10⁶ tonnes CaF₂.

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Résumé En 1974, de la fluorine fut découverte dans la dolomie dite »Hauptdolomit« (Ca₂) et dans la dolomie dite »Plattendolomit» (Ca₃) du Zechstein moyen, près d'Eschwege et de Sontra, en Hesse. Les sondages effectués ainsi que les analyses chimiques et géochimiques ont montré que la fluorine se rencontre de façon stratiforme dans la »Hauptdolomit«, quelquefois en couches et lentilles foncées d'une épaisseur maximale de 0,5 m, ou elle est visible macroscopiquement. La fluorine est souvent présente en faibles teneurs (moins de 10% de CaF₂) dans des couches de 18 à 20 m d'épaisseur; de ce fait, ces dernières ne se distinguent pas de la dolomie gris-blanche exempte de fluorine.La teneur en fluorine varie de 10 % à 50% de CaF₂ dans les couches foncées à noires. Certains échantillons renferment jusqu'à 80% de CaF₂. La coloration foncée est due en partie à la fluorine violette, mais plus encore à la présence de bitume.De la fluorine fut également localisée dans la »Plattendolomit« (Ca₃) de la »LeineSerie Z 3«, qui est située à un niveau stratigraphique supérieur. Cette »Plattendolomit« telle qu'on la rencontre dans les affleurements et carrières des environs de Sontra, contient de 1–4% de CaF₂.L'alternance de fluorine et de dolomie qui, avec sa structure en couches nettement développées, est visible tant macroscopiquement que microscopiquement, ainsi que l'absence de fluorine hydrothermale et d'autres minéraux dans les filons et cassures, sont considérées comme preuves de la formation syn-sédimentaire de la fluorine dans la »Hauptdolomit« (Ca₂) et dans la »Plattendolomit« (Ca₃) de la Hesse. On suppose que la formation de la »Hauptdolomit« est diagénétique tardive. Cette hypothèse devrait également s'appliquer à la fluorine. Il est probable que ce processus a eu lieu dans les lagunes peu profondes à faciès salin. Le fluor provient de l'eau de mer à teneur normale. On peut cependant supposer que la teneur en fluor de l'eau de mer s'est accrue suite à l'apport de fluor provenant du continent, p.ex. à partir de granites riches en fluor du Harz. C'est seulement ainsi que peuvent s'expliquer les grandes quantités de fluorine de la dolomie du Zechstein, en Hesse. Elles sont évaluées entre 5 et 7 · 10⁶ de CaF₂.

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(Ca₂) (Ca₃) . , , , 0,5 . 18–20 , - — CaF₂ 10% — , . 10 50% CaF₂. 80% CaF₂. , . (Ca₃). 1–4% CaF₂. , , ; , . , Ca₂ . . , . . , ., , . . 5–7 × 10⁶ CaF₂.

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Unserem Lehrer, Herrn Professor Dr. Georg Fischer, München, zum 80. Geburtstag gewidmet.     

Variability of water exchanges through the Strait of Hormuz

Ocean Dynamics - The variability of the water mass exchange between the Arabian Gulf and the Indian Ocean is investigated using a high-resolution (1/36°) ocean model. We focus on the period...     

The MAR-Vema Fracture Zone intersection surveyed by deep submersible Nautile

One of the two objectives of the Vemanaute cruise of the French deep submersible Nautile, was the geological study of the eastern intersection area between the Mid-Atlantic Ridge (MAR) and the Vema Fracture Zone in the equatorial Atlantic. Fourteen dives were conducted that allowed detailed geological survey and sampling of the main morphostructural units of this area: the northern and southern walls of the fracture zone, the median ridge, the northern and southern troughs and the nodal basin. In situ observations of recent tectonic features such as furrows, ridges and circular depressions, concentrated within the southern trough, allowed us to establish the location and the size of the present-day displacement zone. Geological investigations have shown that the nodal basin is entirely floored by basalts thus contrasting with other equivalent areas such as the Kane and Oceanographer fracture zone-MAR eastern intersections. Finally, this study stresses the great opposition between the relatively old and tectonically inactive northern part of the fracture, and the southern part which shows active tectonics and recent volcanic activity.     

Earthquake Triggering along the Xianshuihe Fault Zone of Western Sichuan,China

Western Sichuan is among the most seismically active regions in southwestern China and is characterized by frequent strong (M 6.5) earthquakes, mainly along the Xianshuihe fault zone. Historical and instrumental seismicity show a temporal pattern of active periods separated by inactive ones, while in space a remarkable epicenter migration has been observed. During the last active period starting in 1893, the sinistral strike–slip Xianshuihe fault of 350 km total length, was entirely broken with the epicenters of successive strong earthquakes migrating along its strike. This pattern is investigated by resolving changes of Coulomb failure function (CFF) since 1893 and hence the evolution of the stress field in the area during the last 110 years. Coulomb stress changes were calculated assuming that earthquakes can be modeled as static dislocations in an elastic halfspace, and taking into account both the coseismic slip in strong (M 6.5) earthquakes and the slow tectonic stress buildup associated with major fault segments. The stress change calculations were performed for faults of strike, dip, and rake appropriate to the strong events. We evaluate whether these stress changes brought a given strong earthquake closer to, or sent it farther from, failure. It was found that all strong earthquakes, and moreover, the majority of smaller events for which reliable fault plane solutions are available, have occurred on stress–enhanced fault segments providing a convincing case in which Coulomb stress modeling gives insight into the temporal and spatial manifestation of seismic activity. We extend the stress calculations to the year 2025 and provide an assessment for future seismic hazard by identifying the fault segments that are possible sites of future strong earthquakes.     

Seismicity Variations in the Southern Aegean,Greece, Before and After the Large (M7.7) 1956 Amorgos Earthquake Due to Evolving Stress

The largest earthquake (M₀=4.9·10²⁷ dyn·cm) of the 20^th century in the territory of Greece occurred south of Amorgos Island, causing extensive destruction in the southern Aegean area. It occurred on an ENE–trending normal fault that is seated parallel to the Islands southern coastline. Changes in the rates of moderate–size earthquakes (M 5.0) that occurred before and after the Amorgos earthquake, within circular regions centered on its epicenter with radii of 100, 150 and 200 km, are investigated. The rate for moderate–size events just before the main shock appears to be considerably increased when compared to those of either preceding or subsequent periods. Further inspection reveals that more evident seismicity fluctuations are attributed to distances exceeding 100 km. These changes may be indicative of a broad region that is approaching a high stress state prior to an eventual large earthquake. Close to the main event, that is, within the 100–km radius, a remarkable quiescence period lasting about two decades before its occurrence was observed. Changes in seismicity are discussed in combination with static stress changes calculated by the application of the stress evolutionary model that takes into account the coseismic slip associated with the larger events (M 6.5) since the beginning of the 20^th century and the tectonic loading on the major faults in the study area. These larger events, as with the intermediate magnitude seismicity taking place at distances exceeding 100 km and which encircled the quiescent area observed during the last 22 years before the Amorgos earthquake, are well correlated with stress-enhanced areas in each stage of the evolutionary model.