The coast effect in terms of deviated electric currents: a numerical study

A numerical thin-sheet model is used to study the coast effect and to determine the magnitude of the near-surface part of the anomalous field. Theoretical induction arrows are computed for Australia, California, Japan and the British Isles and compared with the observed arrows. This comparison shows that the main part of the coast effect, and in some cases the whole coast effect, is due to the deviation of currents flowing in the ocean by the upper part of the resistive continents. It is suggested that the term ‘coast effect’ should refer to the anomalous field whose source is near-surface. The coast effect so defined behaves like a regional anomaly superimposed on other anomalous features of the transient geomagnetic field. A numerical determination of the geometrical features of the coast effect allows consideration of its elimination. This elimination is performed for California and Japan. A correlation between the resulting residual and heat-flow data is apparent in both cases.     

Simulation of the hydrocarbon structures using the P-SV wave solution

Numerical solution of the scalar and elastic wave equations has greatly aided geophysicists in modeling seismic wave fields in the complicated geologic structures containing hydrocarbons and hence increases the geologic interpretation. Finite-difference method offers a versatile approach to compute synthetic seismograms numerically for given subsurface complex geological structures. To avoid the spatial derivative of the elastic parameters and density, elastodynamic equation (first-order hyperbolic equation) has been solved using the Lax-Wendroff scheme. A numerical finite-difference modeling program has been developed for the P-SV wave using the above solution. A line source with a time delay of 0.015s and dominant frequency of 120 Hz has been utilized in the simulation. In order to avoid the large values of the displacement vector in the source region,Alterman andKaral's method (1968) has been utilized. Horizontal and vertical component synthetic seismograms have been computed for two different geological models with and without oil and gas bearing zones. It has been concluded from the response that a finite-difference technique not only yields the relative arrival times but also accounts for the variation in amplitude and phase according to the elastic impedance contrast across the interfaces. It should come as no surprise to learn that in spite of the limitation of this numerical method, the scheme has provided a valid response for the thin layer, high acoustic impedance contrast and the pinch out.     

Pan-European ground-motion prediction equations for the average horizontal component of PGA,PGV, and 5 %-damped PSA at spectral periods up to 3.0 s using the RESORCE dataset

This article presents a set of Ground-Motion Prediction Equations (GMPEs) for Europe and the Middle East, derived from the RESORCE strong motion data bank, following a standard regression approach. The parametric GMPEs are derived for the peak ground acceleration, peak ground velocity, and 5 %-damped pseudo-absolute acceleration response spectra computed over 23 periods between 0.02 and 3 s, considering the average horizontal-component ground-motions. The GMPEs are valid for distances less than 300 km, hypocentral depth up to 35 km and over the magnitude range 4–7.6. Two metrics for the source-to-station distance (i.e. Joyner-Boore and hypocentral) are considered. The selected dataset is composed by 2,126 recordings (at a period of 0.1 s) related to 365 earthquakes, that includes strong-motion data from 697 stations.The EC8 soil classification (four classes from A to D) discriminates recording sites and four classes (normal, reverse, strike-slip, and unspecified) describe the style of faulting. A subset which contains only stations with measured Vs30 and earthquakes with specified focal mechanism (1,224 records from 345 stations and 255 earthquakes) is used to test of the accuracy of the median prediction and the variability associated to the broader data set. A random effect regression scheme is applied and bootstrap analyses are performed to estimate the 95 % confidence levels for the parameters. The total standard deviation sigma is decomposed into between-events and within-event components, and the site-to-site component is evaluated as well. The results show that the largest contribution to the total sigma is coming from the within-event component. When analyzing the residual distributions, no significant trends are observed that can be ascribed to the earthquake type (mainshock-aftershock classification) or to the non-linear site effects. The proposed GMPEs have lower median values than global models at short periods and large distances, while are consistent with global models at long periods $(\hbox {T} > 1)$  s. Consistency is found with two regional models developed for Turkey and Italy, as the considered dataset is dominated by waveforms recorded in these regions.     

Formation conditions and the environmental state of fresh groundwater in dimitrovgrad area by isotopic-hydrochemical data

Integrated uranium-isotopic and microhydrochemical studies were used to develop an indicator model of formation and circulation of drinking groundwater of Neogene-Quaternary deposit and to assess their current ecological state. The paths of subsurface flows of infiltration recharge are identified and traced, and the zones of deep-water inflow are identified and delimited. The total pollution index of groundwater from Neogene-Quaternary aquifer system was found to far in excess of the acceptable level because of an elevated concentrations of iron, manganese, and phosphorus of anthropogenic and deep-seated origin.     

Potential Impact of Production Chemicals on the Toxicity of Produced Water Discharges from North Sea Oil Platforms

Production chemicals are used on offshore oil production platforms to prevent corrosion and scale formation, and to assist oil–water separation. A proportion of these chemicals may enter the marine environment via the produced water discharge. This study investigated the potential impact of 11 oilfield production chemicals on the toxicity of the produced water discharge. The Microtox® system was used for toxicity assessment of the chemicals, both directly in aqueous preparations and following their partitioning between oil (crude and low toxicity mineral base oil) and North Sea brine. For the majority of the chemicals tested, the toxicity of the aqueous phase to the test organism following partitioning against crude oil, was not significantly altered by the presence of process chemicals when used in their normal field dosage concentrations. However, there was evidence that certain chemicals could increase the partitioning of oil components into the aqueous phase by an order of magnitude, when applied at high dosage concentrations.     

Dynamics of Microbiological Contamination at a Marine Recreational Site

Levels of bacterial indicators of pollution are related with marine salinity and turbidity at both high tide (HT) and low tide (LT). The salinity varied from values around 26.9 ppm at the LT and 28.6 ppm at the high tide but affected total and faecal coliform (FC) estimates. Salinity readings of 25–30 ppm produced microbial counts below 10⁻² MPN/100 ml total coliforms (TCs) whereas salinity of 15–22 ppm produced a TC level of 4.6×10⁻⁴ MPN/100 ml. Turbidity peaks in the samples are accompanied by peaks of microbial contamination of the seawater indicating that the contamination is normally deposited at the marine sediment rather than in the water column. In fact, samples collected under heavy stormy weather, in which the water agitation resulted in turbidity values up to 68.3 NTU, produced maximum microbial counts.     

Seasonal variation of microzooplankton (20–200 μm) and its possible implications on the vertical carbon flux in the western Bay of Bengal

Stratification (throughout the year) and low solar radiation (during monsoon periods) have caused low chlorophyll a and primary production (seasonal average 13–18 mg m⁻² and 242–265 mg C m⁻² d⁻¹, respectively) in the western Bay of Bengal (BoB). The microzooplankton (MZP) community of BoB was numerically dominated by heterotrophic dinoflagellates (HDS) followed by ciliates (CTS). The highest MZP abundance (average 665±226×10⁴ m⁻²), biomass (average 260±145 mg C m⁻²) and species diversity (Shannon weaver index 2.8±0.42 for CTS and 2.6±0.35 for HDS) have occurred during the spring intermonsoon (SIM). This might be due to high abundance of smaller phytoplankton in the western BoB during SIM as a consequence of intense stratification and nitrate limitation (nitracline at 60 m depth). The strong stratification during SIM was biologically evidenced by intense blooms of Trichodesmium erythraeum and frequent Synechococcus–HDS associations. The high abundance of smaller phytoplankton favors microbial food webs where photosynthetic carbon is channeled to higher trophic levels through MZP. This causes less efficient transfer of primary organic carbon to higher trophic levels than through the traditional food web. The microbial food web dominant in the western BoB during SIM might be responsible for the lowest mesozooplankton biomass observed (average 223 mg C m⁻²). The long residence time of the organic carbon in the surface waters due to the active herbivorous pathways of the microbial food web could be a causative factor for the low vertical flux of biogenic carbon during SIM.     

Analysis of Chironomid Remains from Lake Sediments in Paleoecological Reconstruction

The results of methodological studies of paleoecological reconstruction of environmental characteristics are considered. The studies are based on the analysis of chironomid remains from the sediments of lake ecosystems. The investigation is focused on the methodical basis of analysis and the perspectives and range of its application to long-term environmental changes of natural and anthropogenic origin. It is shown that the development of this method in future studies will require a balanced combination of neo- and paleoecological approaches.     

Parametric uncertainty assessment of hydrological models: coupling UNEEC-P and a fuzzy general regression neural network

Due to the complicated nature of environmental processes, consideration of uncertainty is an important part of environmental modelling. In this paper, a new variant of the machine learning-based method for residual estimation and parametric model uncertainty is presented. This method is based on the UNEEC-P (UNcertainty Estimation based on local Errors and Clustering – Parameter) method, but instead of multilayer perceptron uses a “fuzzified” version of the general regression neural network (GRNN). Two hydrological models are chosen and the proposed method is used to evaluate their parametric uncertainty. The approach can be classified as a hybrid uncertainty estimation method, and is compared to the group method of data handling (GMDH) and ordinary kriging with linear external drift (OKLED) methods. It is shown that, in terms of inherent complexity, measured by Akaike information criterion (AIC), the proposed fuzzy GRNN method has advantages over other techniques, while its accuracy is comparable. Statistical metrics on verification datasets demonstrate the capability and appropriate efficiency of the proposed method to estimate the uncertainty of environmental models.