Analysis of microtremors within the Provadia region near a salt leaching mine

By analysis of microtremors recorded with digital seismological monitoring equipment near the Provadia salt diapir (Bulgaria), two groups of events showing different characteristics have been detected in the vicinity of the salt production area. The first group of events has low magnitudes and is located at a distance of about 1 km from the top of the salt diapir. These events show low stress drops. The second group of tremors is located outside the salt diapir. The corresponding magnitudes and stress drops are larger. The first class of events seems to be related to processes at the contour of the salt leaching caverns, whereas the origin of the second group seems to be connected with stress redistribution processes around the salt body. Based on this analysis, the tectonic model of the Provadia salt diapir has been modified.     

A New Method for C k -Surface Approximation from a Set of Curves,with Application to Ship Track Data in the Marianas Trench

We introduce a surface approximation technique to address the problem of fitting a surface to a given set of curves. The originality of the method lies in its ability to take into account the continuous aspect of the data, and also in the possibility to arbitrarily select the regularity (C⁰, C¹, or higher) of the approximant obtained. We demonstrate the efficiency of the approach by constructing a bathymetry map of the Marianas trench based upon a set of SONAR (SOnic Navigation And Ranging) bathymetry ship track data.     

Elastic wave propagation in an irregularly layered medium

The indirect boundary element method (IBEM) is used to simulate wave propagation in two-dimensional irregularly layered elastic media for internal line sources. The method is based on the integral representation for scattered elastic waves using single layer boundary sources. Fulfillment of the boundary conditions leads to a system of integral equations. Results are obtained in the frequency domain and seismograins are computed through Fourier synthesis. In order to test and validate the method we present various comparisons between our results and the time series obtained analytically for a buried line source in a half-space and by using the recently developed spectral element method (SEM).     

Extreme flood‐driven fluvial bank erosion and sediment loads: direct process measurements using integrated Mobile Laser Scanning (MLS) and hydro‐acoustic techniques

This methods paper details the first attempt at monitoring bank erosion, flow and suspended sediment at a site during flooding on the Mekong River induced by the passage of tropical cyclones. We deployed integrated mobile laser scanning (MLS) and multibeam echo sounding (MBES), alongside acoustic Doppler current profiling (aDcp), to directly measure changes in river bank and bed at high (~0.05 m) spatial resolution, in conjunction with measurements of flow and suspended sediment dynamics. We outline the methodological steps used to collect and process this complex point cloud data, and detail the procedures used to process and calibrate the aDcp flow and sediment flux data. A comparison with conventional remote sensing methods of estimating bank erosion, using aerial images and Landsat imagery, reveals that traditional techniques are error prone at the high temporal resolutions required to quantify the patterns and volumes of bank erosion induced by the passage of individual flood events. Our analysis reveals the importance of cyclone‐driven flood events in causing high rates of erosion and suspended sediment transport, with a c. twofold increase in bank erosion volumes and a fourfold increase in suspended sediment volumes in the cyclone‐affected wet season. Copyright © 2016 John Wiley & Sons, Ltd.     

A comment on ‘Far ultraviolet photometry of orion stars’ by G.R. Carruthers

It is shown that the ultraviolet flux-deficiency, recently discovered by Carruthers, in early-type supergiants compared to dwarfs of the same spectral type can be explained in terms of the effects of differences in surface-gravity and effective temperature between stars of these two luminosity classes. It thus appears that this deficiency does not represent a serious discrepancy between theory and observation.     

Stratigraphic and geochemical controls on naturally occurring arsenic in groundwater,eastern Wisconsin,USA

High arsenic concentrations (up to 12,000 7g/L) have been measured in groundwater from a confined sandstone aquifer in eastern Wisconsin. The main arsenic source is a sulfide-bearing secondary cement horizon (SCH) that has variable thickness, morphology, and arsenic concentrations. Arsenic occurs in pyrite and marcasite as well as in iron oxyhydroxides but not as a separate arsenopyrite phase. Nearly identical sulfur isotopic signatures in pyrite and dissolved sulfate and the correlation between dissolved sulfate, iron, and arsenic concentrations suggest that sulfide oxidation is the dominant process controlling arsenic release to groundwater. However, arsenic-bearing oxyhydroxides can potentially provide another arsenic source if reducing conditions develop or if they are transported as colloids in the aquifer. Analysis of well data indicates that the intersection of the SCH with static water levels measured in residential wells is strongly correlated with high concentrations of arsenic in groundwater. Field and laboratory data suggest that the most severe arsenic contamination is caused by localized borehole interactions of air, water, and sulfides. Although arsenic contamination is caused by oxidation of naturally occurring sulfides, it is influenced by water-level fluctuations caused by municipal well pumping or climate changes, which can shift geographic areas in which contamination occurs. Résumé De fortes concentrations en arsenic, jusqu'à 12000 7g/L, ont été mesurées dans l'eau souterraine d'un aquifère gréseux captif, dans l'est du Wisconsin. La principale source d'arsenic est un horizon à cimentation secondaire (SCH) comportant des sulfures, dont l'épaisseur, la morphologie et les concentrations en arsenic sont variables. L'arsenic est présent dans la pyrite et dans la marcassite, de même que dans des oxy-hydroxydes de fer, mais non pas dans une phase séparée d'arsénopyrite. Les signatures isotopiques du soufre presque identiques dans la pyrite et dans les sulfates dissous et la corrélation entre les concentrations en sulfates, en fer et en arsenic dissous laissent penser que l'oxydation des sulfures est le processus dominant contrôlant la libération de l'arsenic dans les eaux souterraines. Cependant, les oxy-hydroxydes contenant de l'arsenic sont susceptibles d'être une autre source d'arsenic si des conditions réductrices apparaissent ou s'ils sont transportés dans l'aquifère sous forme de colloïdes. L'analyse des données provenant de puits montre que l'intersection entre le SCH et les niveaux statiques des puits domestiques est fortement corrélée à de fortes concentrations en arsenic dans les eaux souterraines. Des données de terrain et de laboratoire conduisent à penser que la contamination en arsenic la plus forte est causée par l'interaction localisée aux forages entre l'air, l'eau et les sulfures. Bien que la contamination en arsenic soit causée par l'oxydation de sulfures présents naturellement, elle est influencée par les fluctuations du niveau piézométrique causées par les pompages du captage municipal ou par les variations climatiques, ce qui peut conduire au déplacement des zones géographiques où se produisent les contaminations. Resumen Se han medido concentraciones de arsénico muy altas (de hasta 12000 7g/L) en las aguas subterráneas de un acuífero confinado, en areniscas, localizado en la parte oriental de Wisconsin (EEUU). La fuente principal de arsénico es un horizonte de cementación secundaria (SCH) con un alto contenido en sulfuros, y con una gran variabilidad en espesor, morfología y concentraciones de As. El arsénico aparece en piritas y marcasitas, además de en oxihidróxidos de hierro, pero no como una fase independiente de arsenopiritas. El hecho que la marca isotópica de piritas y sulfatos disueltos sea muy similar, y que exista una gran correlación entre las concentraciones de sulfato disuelto, hierro y arsénico sugiere que la oxidación de sulfuros es el proceso que controla la aportación de arsénico al agua subterránea. Sin embargo, los oxihidróxidos con alto contenido en arsénico podrían suponer otra fuente de arsénico si se llegaran a desarrollar condiciones reductoras o si se transportaran como coloides por el acuífero. De los datos procedentes de pozos, se ve una fuerte correlación entre la presencia de altas concentraciones de As en el agua y que el nivel freático intersecte el SCH. Los datos de campo y de laboratorio indican que los puntos con mayor contaminación de arsénico son debidos a interacciones de carácter local y en los propios pozos entre aire, agua y sulfuros. Aunque la contaminación por As está causada por la oxidación de sulfuros presentes de manera natural, también está muy influenciada por las fluctuaciones en los niveles freáticos causadas por bombeos o cambios climáticos.     

Effects of reservoir stratification and watershed hydrology on manganese and iron in a dam‐regulated river

The presence of metals, including manganese (Mn) and iron (Fe), adversely impacts water quality. In seasonally stratified reservoirs, Mn and Fe can accumulate in the water column due to reducing conditions in sediments and be released to downstream rivers through dam discharge. In addition to reservoir stratification influences, the release of metals downstream is influenced by hydrologic conditions in the river. We examined the seasonal and spatial variability of Mn and Fe concentrations in a eutrophic, hydropower reservoir and the downstream river over a two‐year period. Overall, we found that reservoir stratification was a strong predictor of tailrace Mn and Fe concentrations but that tailrace Fe concentrations were also influenced by dam discharge. Downgradient of the tailrace, river discharge and suspended sediment were the dominant predictors of both Mn and Fe concentrations. Using our data, we develop a conceptual model of seasonal and hydrologic drivers of metal concentrations. The model can be modified for other systems aiding drinking water utilities and other water users in forecasting under what seasonal and hydrologic conditions that Mn and Fe concentrations in river systems are likely to be elevated.     

A review of low‐cost space‐borne data for flood modelling: topography,flood extent and water level

During the last two decades, remote sensing data have led to tremendous progress in advancing flood inundation modelling. In particular, low‐cost space‐borne data can be invaluable for large‐scale flood studies in data‐scarce areas. Various satellite products yield valuable information such as land surface elevation, flood extent and water level, which could potentially contribute to various flood studies. An increasing number of research studies have been dedicated to exploring those low‐cost data towards building, calibration and evaluation, and remote‐sensed information assimilation into hydraulic models. This paper aims at reviewing these recent scientific efforts on the integration of low‐cost space‐borne remote sensing data with flood modelling. Potentials and limitations of those data in flood modelling are discussed. This paper also introduces the future satellite missions and anticipates their likely impacts in flood modelling. Copyright © 2015 John Wiley & Sons, Ltd.     

Quantitative archaeoseismological investigation of the Great Theatre of Larissa, Greece

Larissa, the capital of Thessaly, is located in the eastern part of Central Greece, at the southern border of a Late Quarternary graben, the Tyrnavos Basin. Palaeoseismological, morphotectonic, and geophysical investigations as well as historical and instrumental records show evidences for seismic activity in this area. Previous investigations documented the occurrence of several moderate to strong earthquakes during Holocene time on active faults with recurrence intervals of a few thousand years. The historical and instrumental records suggest a period of seismic quiescence during the last 400–500 years. The present archaeoseismological research, based on a multidisciplinary approach is devoted to improve the knowledge on past earthquakes, which occurred in the area. This study focuses on damages observed on the walls of the scene building of the Great Theatre of Larissa. The Theatre was built at the beginning of the third century BC and consists of a semicircular auditorium, an almost circular arena and a main scene building. Archaeological and historical investigations document a partial destruction of the theatre during the second to first century BC. Recent excavations show that the building complex after it was repaired suffered additional structural damages, probably from seismic loading. The damages investigated in detail are displacements, rotations and ruptures of numerous blocks at the walls of the scene building. In order to test the earthquake hypothesis as cause of the damages a simplified seismotectonic model of the Tyrnavos Basin and its surroundings was used with a composite earthquake source model to calculate synthetic seismograms at the Larissa site for various earthquake scenarios. Horizontal to vertical seismic ratio (HVSR) measurements in the theatre and its vicinity were used to estimate local site effects. The synthetic seismograms are then used as input accelerations for a finite element model of the walls, which simulates seismically induced in-plane sliding within the walls. Results show that some of the surrounding faults have the potential to produce seismic ground motion that can induce in-plane sliding of blocks. Model calculations were used to constrain the characteristics of the ground acceleration and infer the causative fault and earthquake by comparing the calculated and observed distribution of the displacements of the blocks. Ground motions with a PGA at the site of 0.62–0.82 g, which could be induced by an M 5.8–6.0 earthquake on the nearby Larissa Fault, would be sufficient to explain the damage.