Ground deformation of Nisyros Volcano (Greece) for the period 1995–2002: Results from DInSAR and DGPS observations

Differential GPS (DGPS) and Differential Interferometric Synthetic Aperture Radar (DInSAR) analyses were applied to the Kos-Yali-Nisyros Volcanic Field (SE Hellenic Volcanic Arc) to quantify the ground deformation of Nisyros Volcano. After intense seismic activity in 1996, a GPS network was installed in June 1997 and re-occupied annually up to 2002. A general uplift ranging from 14 to 140 mm was determined at all stations of the network. The corresponding horizontal displacements ranged from 13 to 53 mm. The displacement vectors indicate that the island is undergoing extension towards the East, West and South. A two-source “Mogi” model combined with assumed motion along the Mandraki Fault was constructed to fit the observed deformation. The best-fit model assumes sources at a depth of 5500 m NW of the centre of the island and at 6500 m offshore ESE of Yali Island. DInSAR analysis using four pairs of images taken between May 1995 and September 2000 suggests that deformation was occurring during 1995 before the start of the seismic crisis. An amplitude of at least 56 mm along the slant range appeared for the period 1996 through 1999. This deformation is consistent with the two-source model invoked in DGPS modelling. Surface evidence of ground deformation is expressed in the contemporaneous reactivation of the Mandraki Fault. In addition, a 600 m long N-S trending irregular rupture in the caldera floor was formed between 2001 and 2002. This rupture is interpreted as the release of surface stress in the consolidated epiclastic and hydrothermal sediments of the caldera floor.     

Sedimentologische Untersuchungen an Grimmelfinger Graupensanden

Zusammenfassung Die Untersuchung von Korngrößenverteilung und Rundungsgrad der Grimmelfinger Graupensande an zwei durch 150 km Transportweg unterschiedenen Aufschlüssen gibt Hinweise auf die Einwirkungen auf das verfrachtete Sedimentmaterial unter gleichförmigen, fluviatilen Bedingungen.Am Anfang des untersuchten Rinnenabschnittes besteht das Sediment überwiegend aus je einer Modalfraktion im Mittelsandbereich, Grobsandbereich und Feinkiesbereich¹.Auf dem Transport wird die Mittelsandfraktion — vermutlich infolge der Schlagwirkung des Feinkieses — aufgerieben und fortgeführt. In den beiden gröberen Fraktionen wird am Ende des untersuchten Abschnittes keine Korngrößenabnahme und damit verbunden auch keine Rundungsgraderhöhung beobachtet. Dieses Ergebnis wird verglichen mit den in der Literatur mitgeteilten Untersuchungen in Abriebmühlen und Feldbeobachtungen. Danach dürfte der Rundungsgrad in der Feinkiesfraktion seinem unter den gegebenen Umständen erreichbaren Grenzwert sehr nahe sein und sich auch bei weiter fortgesetztem Transport kaum noch ändern. In der Grobsandfraktion wird der Anteil, dessen Rundung verbessert wird, infolge der damit verbundenen höheren Kugeligkeit bevorzugt fortgeführt.Die Untersuchungen bestätigen, daß die Abrundungseffekte an Sedimentmaterial in strömendem Wasser in Abhängigkeit von der Korngröße betrachtet werden müssen.

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The mechanical effects of fluvial transport over a distance of 150 km were studied by means of size frequency distributions and analysis of roundness in a Tertiary flow channel in Southern Germany filled by sand mixed with fine gravel.When entering the-channel the deposited material shows characteristic trimodal size frequency distributions. During transport the finer modal fraction (0.2...0.63 mm) is destroyed — probably through breakage by the gravel — and removed, while the sizes of the two coarser fractions remain unaffected. The roundness of the coarser fractions also remains unchanged by transport. This suggests that the roundness of the gravel material has approached its limiting roundness which is the optimum that can be achieved under the prevailing conditions. That part of the coarse sand fraction which becomes better rounded by transport may be removed preferably, because the grains getting higher sphericity by being rounded are transported more easily.Grain sizes have to be considered when abrasion effects are studied.

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Herrn Professor Dr. H. Aldinger danke ich für die Möglichkeit, die vorliegende Arbeit im Geologisch-Paläontologischen Institut der Technischen Hochschule Stuttgart anzufertigen, Herrn Dr. D. Elwert, Kiel, für die Überlassung von Probenmaterial.     

From outwash to coastal systems in the Portneuf–Forestville deltaic complex (Québec North Shore): Anatomy of a forced regressive deglacial sequence

Deglacial sequences typically include backstepping grounding zone wedges and prevailing glaciomarine depositional facies. However, in coastal domains, deglacial sequences are dominated by depositional systems ranging from turbiditic to fluvial facies. Such deglacial sequences are strongly impacted by glacio‐isostatic rebound, the rate and amplitude of which commonly outpaces those of post‐glacial eustatic sea‐level rise. This results in a sustained relative sea‐level fall covering the entire depositional time interval. This paper examines a Late Quaternary, forced regressive, deglacial sequence located on the North Shore of the St. Lawrence Estuary (Portneuf Peninsula, Québec, Canada) and aims to decipher the main controls that governed its stratigraphic architecture. The forced regressive deglacial sequence forms a thick (>100 m) and extensive (>100 km²) multiphased deltaic complex emplaced after the retreat of the Laurentide Ice Sheet margin from the study area ca 12 500 years ago. The sedimentary succession is composed of ice‐contact, glaciomarine, turbiditic, deltaic, fluvial and coastal depositional units. A four‐stage development is recognized: (i) an early ice‐contact stage (esker, glaciomarine mud and outwash fan); (ii) an in‐valley progradational stage (fjord head or moraine‐dammed lacustrine deltas) fed by glacigenics; (iii) an open‐coast deltaic progradation, when proglacial depositional systems expanded beyond the valley outlets and merged together; and (iv) a final stage of river entrenchment and shallow marine reworking that affected the previously emplaced deltaic complex. Most of the sedimentary volume (10 to 15 km³) was emplaced during the three‐first stages over a ca 2 kyr interval. In spite of sustained high rates of relative sea‐level fall (50 to 30 mm·year^?1), delta plain accretion occurred up to the end of the proglacial open‐coast progradational stage. River entrenchment only occurred later, after a significant decrease in the relative sea‐level fall rates (<30 mm·year^?1), and was concurrent with the formation and preservation of extensive coastal deposits (raised beaches, spit platform and barrier sands). The turnaround from delta plain accretion to river entrenchment and coastal erosion is interpreted to be a consequence of the retreat of the ice margin from the river drainage basins that led to the drastic drop of sediment supply and the abrupt decrease in progradation rates. The main internal stratigraphic discontinuity within the forced regressive deglacial sequence does not reflect changes in relative sea‐level variations.     

Assessment of small-diameter shallow wells for managed aquifer recharge at a site in southern Styria,Austria

An approach to establish the recharge component of managed aquifer recharge (MAR) has recently been proposed that uses small-diameter shallow wells installed using relatively inexpensive drilling methods such as direct push. As part of further development of that approach, a generalized procedure is presented for a technical and economic assessment of the approach’s potential in comparison to other systems. Following this procedure, the use of small-diameter wells was evaluated both experimentally and numerically for a site located in southern Styria, Austria. MAR is currently done at the site using a horizontal pipe infiltration system, and system expansion has been proposed with a target rate of 12 l/s using small-diameter wells as one possible option. A short-duration single-well field recharge experiment (recharge rate 1.3–3.5 l/s) was performed (recharge by gravity only). Numerical modeling of the injection test was used to estimate hydraulic conductivity (K). Quasi-steady-state, single-well recharge simulations for different locations, as well as a long-term transient simulation, were performed using the K value calibrated from the field injection test. Results indicate that a recharge capacity of 4.1 l/s was achievable with a maximum head rise of 0.2 m at the injection well. Finally, simulations were performed for three different well fields (4, 6 and 8 wells, respectively) designed to infiltrate a target rate of 12 l/s. The experimental and numerical assessments, supported by a cost analysis of the small-diameter wells, indicate that the small-diameter wells are a viable, cost-effective recharge approach at this and other similar sites.     

Einfluß der Gezeitenstromturbulenz auf die hydrographische Schichtung der Nordsee

Zusammenfassung Es wird das kritische vertikale Dichtegefälle ermittelt, das die Gezeitenstromturbulenz, die vom Meeresboden ausgeht, zum Erliegen bringt (Abb. 2). Ihm wird jenes vertikale Dichtegefälle gegenübergestellt, das der tägliche Wärmestrom durch die Turbulenz der winderzeugten Oberflächenströmungen bewirkt (Abb. 3). In derjeningen Tiefe, in der beide Gefällswerte gleich werden, liegt die Obergrenze der bodennahen Mischungsschicht, deren Verteilung in der Nordsee auf zwei ozeanographischen Schnitten verfolgt wird, die mit dem Vermessungs- und Forschungsschiff Gauss im August 1953 ausgeführt wurden (Abb. 1). Der eine Schnitt verläuft vom Nordausgang der Nordsee zu den westfriesischen Inseln, der andere von der schottischen zur norwegischen Küste (Abb. 4). Durch diese Anordnung konnten alle charakteristischen sommerlichen Lagen in der Nordsee erfaßt werden: der Übergang von der unbedeutenden bodennahen Mischungsschicht in der nördlichen Nordsee zur mächtigen Mischungsschicht der mittleren Nordsee, die dort in den Gebieten mit höheren Gezeitenströmen die normale sommerliche Sprungschicht zu einer wenige Dezimeter dicken Schicht zusammendrängt und die in den Gebieten mit starken Gezeitenströmen in die oberflächennahe Mischungsschicht übergreift. Als Folge davon wird in ausgedehnten Gebieten Schichtungslosigkeit während des ganzen Jahres aufrechterhalten. Die weitreichenden, verschiedenartigen Einflüsse dieser Mischungsvorgänge machen sich unter anderem auf den Jahresgang der Oberflächentemperatur der Nordsee deutlich bemerkbar (Abb. 5 und 6).

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Summary The critical vertical density gradient for suppressing the tidal current turbulence which originates from the bottom of the sea is determined (fig. 2). It is compared with the vertical density gradient caused by the daily heat transport in consequence of the turbulence of the wind-produced surface currents (fig. 3). At the depth where the two gradients become equal there lies the upper limit of the mixed ground layer. Its distribution in the North Sea is shown by two oceanographic profiles on the basis of measurements carried out by the survey and research ship Gauss in April 1953 (fig. 1). One profile extends from the northern exit of the North Sea to the West-Frisian islands, the other one from the Scotch to the Norwegian coast (fig. 4). By this arrangement all characteristic summer situations in the North Sea could be included: the change from the small mixed ground layer in the northern North Sea to the mighty mixed ground layer of the central North Sea compressing there, in regions with higher tidal currents, the normal summer discontinuity layer to a few decimeters and, in regions with strong tidal currents, reaching into the mixed surface layer. As a consequence in vast regions a state without stratification is maintained during the whole year. The far-reaching and various influences of these mixing processes, e. g. on the annual variation of the surface temperature of the North Sea, are evident (fig. 5 and 6).

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Résumé On recherche le gradient vertical critique de densité capable d'annuller le remous dû à la marée au fond de la mer (fig. 2) et on le compare au même gradient produit par le réchauffement diurne combiné avec la turbulence des courants de surface dûs au vent (fig. 3). La profondeur à laquelle ces deux gradients sont identiques fixe la limite supérieure de la couche de mélange voisine du fond. La distribution de cette couche dans la Mer du Nord ressort de deux profils relevés par le navire océanographique Gauss en août 1953 (fig. 1). L'un des profils va de l'extrémité septentrionale de cette mer jusqu'aux îles occidentales de la Frise; l'autre s'étend de la côte écossaise à celle de la Norvège (fig. 4). De cette façon une étude de tous les caractères estivaux de la Mer du Nord met en évidence le passage de la faible couche de mélange dans le Nord à la couche très importante dans la région moyenne; cette dernière couche a pour effet de réduire à quelques décimètres la couche de transition estivale normale dans les régions à courants de marée profonds tandis qu'elle pénètre dans la couche de mélange de surface dans les régions à forts courants de marée. En vertu de ces processus, l'absence de stratification se maintient pendant toute l'année dans de vastes régions. Les effets variés et lointains de ces phénomènes de mélange se font nettement sentir, entre autres, sur la variation annuelle de la température de surface dans la Mer du Nord (fig. 5 et 6).

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Mit 6 Textabbildungen.     

The operational weather radar of Fossalon di Grado (Gorizia, Italy): accuracy of reflectivity and differential reflectivity measurements

Summary The error structure of radar measurements should be accurately known in order to provide reliable estimates for a number of quantitative meteorological applications, from rainfall rate estimation to cloud microphysics. The aim of this paper is to give a detailed characterization of Z _H and Z _DR measurements obtained by the weather radar of Fossalon di Grado (Gorizia, Italy). Vertical-looking observations are used to determine the system bias on differential reflectivity and to estimate the measurement error on both Z _H and Z _DR in the rain medium. It is estimated that no bias is affecting Z _DR and the accuracy of Z _H and Z _DR is 0.8 and 0.1 dB, respectively. A similar evaluation is done in the rain medium at larger ranges with the antenna pointing at low elevation angles. The long time stability of the absolute reflectivity calibration is also established by radar-rain gage inter-comparison over almost 200 hours of precipitation data collected during nearly two years. Received June 21, 2001 Revised November 13, 2001     

Observations of vertical ground accelerations exceeding gravity during the 1997 Umbria-Marche (central Italy) earthquakes

We found extensive evidence that the vertical ground accelerations produced during the largest shock (M = 6.0) of the 1997 Umbria-Marche earthquake sequence exceeded 1g in two areas close to the heavily-damaged villages of Annifo and Colle Croce. This evidence comes from the striking observation of thousands of freshly fractured and broken rocks and stones in these areas. Some of the broken stones lie isolated on soft detritic soil while others had been previously piled up, probably a long time agoto clear the fields for farming. The freshness of the cuts and fractures and the consistency of the observations for thousands of rocks and stones in these areas indicate that these rocks were thrown upwards during the earthquake, with breakage occurring at the time of impact. Ground motion calculations consistent with the static deformation inferred from GPS and interferometry data, show that the broken stones and rocks are found in the zone where the strongest shaking took place during the earthquake and that most of the shaking there was vertical.