Coseismic slip model of the 2007 August Pisco earthquake (Peru) as constrained by Wide Swath radar observations

The Pisco earthquake ( M _w 8.0; 2007 August 15) occurred offshore of Peru's southern coast at the subduction interface between the Nazca and South American plates. It ruptured a previously identified seismic gap along the Peruvian margin. We use Wide Swath InSAR observations acquired by the Envisat satellite in descending and ascending orbits to constrain coseismic slip distribution of this subduction earthquake. The data show movement of the coastal regions by as much as 85 cm in the line-of-sight of the satellite. Distributed-slip model indicates that the coseismic slip reaches values of about 5.5 m at a depth of ∼18–20 km. The slip is confined to less than 40 km depth, with most of the moment release located on the shallow parts of the interface above 30 km depth. The region with maximum coseismic slip in the InSAR model is located offshore, close to the seismic moment centroid location. The geodetic estimate of seismic moment is 1.23 × 10²¹ Nm ( M _w 8.06), consistent with seismic estimates. The slip model inferred from the InSAR observations suggests that the Pisco earthquake ruptured only a portion of the seismic gap zone in Peru between 13.5° S and 14.5° S, hence there is still a significant seismic gap to the south of the 2007 event that has not experienced a large earthquake since at least 1687.     

Stochastic rainfall-runoff forecasting: parameter estimation,multi-step prediction,and evaluation of overflow risk

Probabilistic runoff forecasts generated by stochastic greybox models can be notably useful for the improvement of the decision-making process in real-time control setups for urban drainage systems because the prediction risk relationships in these systems are often highly nonlinear. To date, research has primarily focused on one-step-ahead flow predictions for identifying, estimating, and evaluating greybox models. For control purposes, however, stochastic predictions are required for longer forecast horizons and for the prediction of runoff volumes, rather than flows. This article therefore analyzes the quality of multistep ahead forecasts of runoff volume and considers new estimation methods based on scoring rules for k-step-ahead predictions. The study shows that the score-based methods are, in principle, suitable for the estimation of model parameters and can therefore help the identification of models for cases with noisy in-sewer observations. For the prediction of the overflow risk, no improvement was demonstrated through the application of stochastic forecasts instead of point predictions, although this result is thought to be caused by the notably simplified setup used in this analysis. In conclusion, further research must focus on the development of model structures that allow the proper separation of dry and wet weather uncertainties and simulate runoff uncertainties depending on the rainfall input.     

Specific angular momentum of disc merger remnants and the λR-parameter

We use two-dimensional kinematic maps of simulated binary disc mergers to investigate the  λ_R  -parameter, which is a luminosity-weighted measure of projected angular momentum per unit mass. This parameter was introduced to subdivide the SAURON sample of early-type galaxies in so-called fast  λ_R > 0.1  and slow rotators  λ_R < 0.1  . Tests on merger remnants reveal that  λ_R  is a robust indicator of the true angular momentum content in elliptical galaxies. We find the same range of  λ_R  values in our merger remnants as in the SAURON galaxies. The merger mass ratio is decisive in transforming fast rotators into slow rotators in a single binary merger, the latter being created mostly in an equal-mass merger. Slow rotators have a  λ_R  which does not vary with projection. The confusion rate with face-on fast rotators is very small. Mergers with a gas component form slow rotators with smaller ellipticities than collisionless merger remnants have, and are in much better agreement with the SAURON slow rotators. Remergers of merger remnants are slow rotators, but tend to have too high ellipticities. Fast rotators maintain the angular momentum content from the progenitor disc galaxy if merger mass ratio is high. Some SAURON galaxies have values of  λ _R   as high as our progenitor disc galaxies.     

Tracking the fate of dung-derived carbohydrates in a temperate grassland soil using compound-specific stable isotope analysis

Carbohydrates are major organic components of dung and are likely to contribute substantially to increased carbon stocks in manured soils. To investigate this hypothesis, a field-scale experiment was conducted on a temperate grassland site in Devon, UK. C₄ dung (bulk δ¹³C value ?12.6‰) was applied to a temperate grassland C₃ soil (bulk δ¹³C value ?30.3‰) in April and the surface soil beneath cow pats sampled at seven dates over a year. Total carbohydrates were extracted as their monosaccharide components and analysed as the alditol acetates using gas chromatography. The δ¹³C values of the major monosaccharides glucose (?11.5 ±0.6‰), xylose (?10.4 ±0.4‰), arabinose (?10.4 ±0.5‰) and galactose (?8.3 ±1.6‰) extracted from the C₄ dung via acid hydrolysis were indicative of their source. Their weighted mean δ¹³C value was ?10.8‰, 1.8‰ more ¹³C-enriched than the bulk dung value. The δ¹³C values of individual monosaccharides recovered by acid hydrolysis in the 0–1 cm and 1–5 cm soil horizons beneath C₄ cow pats, compared with control soils determined over 372 days, allowed assessment of the extent of incorporation and fluxes of dung-derived monosaccharides. A maximum of 60% of the dung C in soil was derived from carbohydrates after 56 days, declining to around 20% after 372 days. Incorporation dynamics varied between monosaccharide species. Glucose, xylose and arabinose behaved in a similar manner because of their predominantly plant cell wall derived provenance in the dung, whilst dung-derived galactose and mannose appeared to have a microbial source in the soil. The dynamics of total dung-derived monosaccharides in the top 5 cm was comparable to incorporation and flux of bulk dung C, previously estimated using bulk δ¹³C values. The movement of dung-derived carbohydrates into the soil was inequivalent between the 0–1 cm and 1–5 cm horizons. The lack of a significant difference in concentration, but the evidence for the persistence of dung-derived monosaccharides in soil based on δ¹³C values, indicated replacement of existing pools in the soil, suggesting that the ability of this particular soil to sequester further C derived from carbohydrates was limited.     

Hydrous aluminosilicate metasomatism in an intra-oceanic subduction zone: Implications from the Kurancali (Turkey) ultramafic-mafic cumulates within the Alpine Neotethys Ocean

The Kurancali ultramafic-mafic cumulate body, an allochthonous ophiolitic sliver in central Anatolia, is characterized by the presence of abundant hydrous phases (phlogopite, pargasite) besides augitic diopside, plagioclase, and accessory amounts of rutile, sphene, apatite, zircon, and calcite. Based on modes of the essential minerals, the olivine-orthopyroxene-free cumulates are grouped as clinopyroxenite, hydrous clinopyroxenite, phlogopitite, hornblendite, layered gabbro, and diorite. Petrographical, mineralogical and geochemical features of the rocks infer crystallization from a hydrous magma having high-K calc-alkaline affinity with slightly alkaline character, and point to metasomatised mantle as the magma source. Our evidence implies that the metasomatising component, which modified the composition of the mantle wedge source rock in an intra-oceanic subduction zone, was a H₂O, alkali and carbonate-rich aluminosilicate fluid and/or melt, probably derived from a subducted slab. We suggest that the metasomatic agents in the subarc mantle led to the generation of a hydrous magma, which produced the Kurancali cumulates in an island-arc basement in a supra-subduction-zone setting during the closure of the Izmir-Ankara-Erzincan branch of the Alpine Neotethys Ocean.     

Can plankton communities be considered as bio-indicators of water quality in the Lagoon of Venice?

This study examines whether plankton of the Lagoon of Venice could be considered as a bio-indicator of areas subjected to various anthropogenic influences. This study was a two year hydrochemical and biological survey in five areas of the Lagoon of Venice, each with different environmental conditions due to pollution from urban, industrial, thermal and agricultural wastes. Phytoplankton associations did not show any promising species. In the different lagoonal areas, this community was differentiated into its major groups. In contrast, the copepod Acartia tonsa Dana could be considered as a target species in highly eutrophic areas.     

Fully coupled modeling of seabed subsidence and reservoir compaction of North Sea oil fields

This paper focuses on the aspects of fully coupled continuum modeling of multiphase poroelasticity applied to the three-dimensional numerical simulations of the Ekofisk oil reservoir in the North Sea (56°29′–34′N, 03°10′–14′E). A systematic presentation is chosen to present the methodology behind fully coupled, continuum modeling. First, a historical review of the subsidence phenomena above an oil and gas reservoir is given. This will serve as a background against which the relevance of the present approach to compaction and subsidence modeling will be demonstrated. Following this, the governing equations for a multiphase poroelasticity model are briefly presented. Particular attention is paid to the analysis of the pore-compressibility term usually used in an uncoupled approach for characterising the host-rock deformation. A comparative numerical analysis is carried out to contrast and highlight the difference between coupled and uncoupled reservoir simulators. Finally, a finite-element numerical model of the Ekofisk field is presented and a significant result is a contour map of seabed subsidence which is in general agreement with the shape of the subsidence contours based on past bathymetric surveys. Analysis of the simulation reveals that, due to the downward movement of the overburden, oil migration occurs from the crest of the anticline in which the field is situated, towards the flank. The pore-pressure depletion in the reservoir is significantly delayed due to the replenishment of the reservoir energy via the formational compaction. Horizontal movement in the reservoir, which is neglected in traditional modeling, can be significant and comparable in magnitude to the vertical subsidence. Electronic Publication     

Holocene environmental change at Lake Njulla (999 m a.s.l.), northern Sweden: a comparison with four small nearby lakes alongan altitudinal gradient

We assess Holocene environmental change at alpine Lake Njulla(68°22N, 18°42E, 999 m a.s.l.) innorthernmost Sweden using sedimentary remains of chironomid head capsules anddiatoms. We apply regional calibration sets to quantitatively reconstruct meanJuly air temperature (using chironomids and diatoms) and lake-water pH(using diatoms). Both chironomids and diatoms infer highest temperatures(1.7–2.3°C above present-day estimates, includinga correction for glacio-isostatic land up-lift by0.6°C) during the early Holocene (c.9,500–8,500 cal. yrs BP). Diatoms suggest a decreasing lake-waterpH trend (c. 0.6 pH units) since the early Holocene. Usingdetrended canonical correspondence analysis (DCCA), we compare the Holocenedevelopment of diatom communities in Lake Njulla with four other nearby lakes(Lake 850, Lake Tibetanus, Vuoskkujávri, Vuolep Njakajaure) locatedalong an altitudinal gradient. All five lakes show similar initial DCCA scoresafter deglaciation, suggesting that similar environmental processes such ashigh erosion rates and low light availability associated with high summertemperature appear to have regulated the diatom community, favouring highabundances of Fragilaria species. Subsequently, the diatomassemblages develop in a directional manner, but timing and scale ofdevelopment differ substantially between lakes. This is attributed primarily todifferences in the local geology, which is controlling the lake-waterpH. Imposed on the basic geological setting, site-specific processessuch as vegetation development, climate, hydrological setting andin-lake processes appear to control lake development in northernSweden.     

Numerical calculation of weakly singular surface integrals

We consider semi-analytical and purely numerical integration methods for weakly singular integrals with point singularities on curved smooth surfaces. The methods can be applied to many practical computations in Geodesy, e.g. terrain corrections, Stokes' and Hotines' integral, surface potentials, and the solution of geodetic boundary value problems using integral equations. Current numerical integration techniques are reviewed. The most important semi-analytical and purely numerical techniques are described. Test calcualtions are done and the techniques are compared as regards accuracy and computational efficiency. Semi-analytical methods, which are based on some regularizing parameter transformations, are superior to purely numerical techniques. The best choice are modified polar coordinates defined in the parameter domain with the singularity as pole. Triangular coordinates show similar performance if carefully tuned. Extrapolation techniques and adaptive subdivision techniques behave poorly as regards accuracy and numerical efficiency. Standard integration techniques, which ignore the singularity, completely fail.     

Influence of artificial groundwater lakes on the abundance and activity of bacteria in adjacent subsurface systems

Bacterial abundances and activity, estimated by 4′,6-diamidino-2-phenylindole staining (DAPI) and the reduction of 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride (INT), were investigated in two oligotrophic artificial groundwater lakes and the surrounding aquifers. To evaluate the effect of lake water on groundwater downstream, samples were taken from wells at different distances from the lakes, and the total number of bacteria and the number of active bacteria in these samples were compared with samples collected upstream. In addition, sterilized sandy sediments were exposed in groundwater wells to measure the number and activity of bacteria attached to particles. At one of the study sites, where the lake sediments were disturbed by dredging, total bacterial abundance and the number of respiring bacteria in the groundwater aquifer was clearly influenced by the lake water. The average bacterial abundances decreased from 2.6 ± 1.9 × 10⁵ cells ml⁻¹ in the well closest to the lake (S2) to 2.9 ± 3.8 × 10⁴ cells ml⁻¹ in the most distant one (S4), which was equivalent to cell numbers in the upstream well. The number of respiring bacteria showed a similar tendency with 1.3 ± 2.7 × 10⁴ active cells ml⁻¹ in S2 and 1.9 ± 1.5 × 10³ active cells ml⁻¹ in S4. At the second study site, which was not influenced by dredging, bacteria in the downstream wells seemed not to be affected by the lake water. The number and activity of bacteria, which colonized exposed sediments, were not significantly different in the upstream and downstream wells, indicating a minor influence of lake water on this habitat. Our results suggest that gravel-pit lakes may influence the free living bacterial assemblages in nearshore groundwater systems, but do not visibly affect numbers and activity of bacteria attached to the surface of aquifer sediments.