Saxothuringian-Moldanubian Suture and Predisposition of Seismicity In The Western Bohemian Massif

We modelled the thickness and seismic anisotropy of the subcrustal lithosphere from the variations of P-wave delay times and the shear-wave splitting observed at seismological observatories and portable stations in the western part of the Bohemian Massif. The Saxothuringian lithosphere is characterized by a total thickness between 90 and 120 km, the Moldanubian lithosphere is generally thicker –120-140 km, on the average. The subcrustal lithosphere of both units is characterised by divergently dipping anisotropic structures and the suture between them is marked by a lithosphere thinning to about 80km. Within the subcrustal lithosphere a complex structure of the transition of both units extends to about 150 km toward the south. We suggest that the Saxothuringian-Moldanubian suture has created a zone of mechanical predisposition for the Tertiary Ohe (Eger) Graben, as well as for the occurrence of earthquake swarms in the region. Most earthquakes occur within the brittle part of the upper crust above the crossing of the suture between the Saxothuringian in the north and the Moldanubian and the Tepl´-Barrandian in the south, with the tectonically active Mariánské Lázn fault.     

Microbiologically influenced corrosion in dairy effluent

In the dairy industry mild steel is used as the construction material for the effluent treatment plants, pipelines, reinforcement in concrete structures etc. The steel exposed to the dairy effluent faces corrosion due to the microbes. In the present study the role of microbes in dairy effluent on the corrosion of mild steel has been investigated. Pseudomonas sp., Streptococcus sp., Micrococcus sp., Bacillus sp., Neisseria sp. and Lactobacillus sp. were identified in dairy effluent. Corrosion rate has been estimated by weight loss measurements and polarization technique. The Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometer (XRD) studies were found helpful in investigating the chemical pathway leading to the formation of corrosion products on the mild steel during fermentation. Initiation of pitting corrosion was noticed on steel specimens by scanning electron microscope (SEM). A mechanism has been proposed for microbiologically influenced corrosion in dairy effluent.     

Differential Alteration of Ilmenite in a Tropical Beach Placer, Southern India: Microscopic and Electron Probe Evidences

Abstract. The study based on microscopic and microprobe techniques reveals that ilmenite of Manavalakurichi deposit has generally reached the alteration phase of 'leached ilmenite'. The XRD and bulk chemical analysis confirm the limited alteration undergone by ilmenite grains. Ilmenite alteration has been found to be a process of continuous leaching of iron from the mineral lattice and hydroxylisation. The enrichment of trace elements with progressive alteration is discussed. Si and Al are enriched by more than 100 fold. The prevalence of reducing environment at present in the deposit indicates that the oxidation of ferrous iron leading to pseudorutile formation would have occurred during transportation of sediments.     

Web-based resources on software GPS receivers

This column provides the Web-based GPS resources and their technical background information. Its purpose is to inform the reader about the data, software, electronic documents that are available online. This column is coordinated by Dr. Jinling Wang, The University of New South Wales, Sydney. Comments and suggestions are appreciated (jinling.wang@unsw.edu.au). In this issue’s column, Mr. Ravindra Babu introduces the online resources on software GPS receivers.     

Characteristic Study of the Boundary Layer Parameters over the Arabian Sea and the Bay of Bengal Using the QuikSCAT Dataset

The marine atmospheric boundary layer （MABL） plays a vital role in the transport of momentum and heat from the surface of the ocean into the atmosphere. A detailed study on the MABL characteristics was carried out using high-resolution surface-wind data as measured by the QuikSCAT （Quick scatterometer） satellite. Spatial variations in the surface wind, frictional velocity, roughness parameter and drag coefficient for the different seasons were studied. The surface wind was strong during the southwest monsoon season due to the modulation induced by the Low Level Jetstream. The drag coefficient was larger during this season, due to the strong winds and was lower during the winter months. The spatial variations in the frictional velocity over the seas was small during the post-monsoon season （-0.2 m s^-1）. The maximum spatial variation in the frictional velocity was found over the south Arabian Sea （0.3 to 0.5 m s^-1） during the southwest monsoon period, followed by the pre-monsoon over the Bay of Bengal （0.1 to 0.25 m s^-1）. The mean wind-stress curl during the winter was positive over the equatorial region, with a maximum value of 1.5×10^-7 N m^-3, but on either side of the equatorial belt, a negative wind-stress curl dominated. The area average of the frictional velocity and drag coefficient over the Arabian Sea and Bay of Bengal were also studied. The values of frictional velocity shows a variability that is similar to the intraseasonal oscillation （ISO） and this was confirmed via wavelet analysis. In the case of the drag coefficient, the prominent oscillations were ISO and quasi-biweekly mode （QBM）. The interrelationship between the drag coefficient and the frictional velocity with wind speed in both the Arabian Sea and the Bay of Bengal was also studied.     

Three-dimensional analysis of gravity anomalies of sedimentary basins by polygonal prismatic model with a quadratic density function

The decrease of density contrast in sedimentary strata may be approximated by a quadratic function. A sedimentary basin may be considered as a number of horizontal polygonal prisms of finite thickness placed one over the other. Equations for the gravity anomaly of ann-sided polygon prism have been derived using a quadratic density function. A method has been developed for inversion of the gravity anomalies using a polygonal prismatic model. An analytical method has been employed for evaluating the necessary derivatives as the computing time by this method is much slower than by a numerical method. Approximate equations have been derived for rapid calculation of the anomalies and derivatives. Efficient computer programs have been developed for calculation of the anomalies and derivatives by an appropriate use of the exact and approximate equations. The depths to the polygon prisms constituting the basin are iteratively adjusted by minimizing the sum of the squares of the differences between the observed and calculated anomalies. These methods have been applied to analyze the Bouguer anomaly map of the Los Angeles basin, California.     

Application of the Hilbert transform for gravity and magnetic interpretation

Either the magnetic anomaly or the horizontal gradient of gravity, if plotted against its Hilbert transform and then joined by a smooth curve, the relation figure is obtained. Properties of relation figures for some two-dimensional sources of simple geometry are shown to be useful in distinguishing the source geometry and also in estimating the source parameters, even in the presence of remanence.     

A new technique of interpreting gravity and vertical magnetic anomalies due to infinite horizontal cylindrical ore bodies

Summary A novel method of interpreting gravity and magnetic anomalies is presented here. Two diagrams of master curves, one for gravity and the other for vertical magnetic interpretation are presented. They are useful in calculating the depth of burial and the radius of infinite horizontal cylindrical bodies irrespective of density contrast or strength and direction of magnetisation. This method also enables us to infer the direction of magnetisation, resultant intensity of magnetisation and from them the susceptibility contrast; and density contrast. ThoughHenderson [8]²) reported the applicability of continuations and derivatives in the interpretation of magnetic anomalies for the first time, the authors have treated them in a more exhaustive manner in the present paper to obtain valuable relationships.     

Regional anomalies of P-wave amplitudes and tectonics of focal regions

A distinct regional dependence of amplitude observations at closely-situated pairs of Central European seismic stations (about 1° apart) was observed for the short-period P waves at teleseismic distances. For the investigated regions, namely Japan, the Kuriles, Kamchatka, the Aleutians, and Alaska, the magnitude corrections change by 0.3 magnitude units. These changes are related to the change of the strike and dip of the sinking lithospheric plates. A relative decrease of the amplitudes, generally observed for different pairs of stations, corresponds to a decrease of the angle between a seismic ray and a slab.