HIGH-RESOLUTION PREDICTION OF ACOUSTIC IMPEDANCES BELOW BOTTOM-OF-HOLE*

Prediction of acoustic impedances below bottom-of-hole developed in the paper is based on VSP data processing. The pulse form and reflections are deduced from records on the vertical array by the method of subtraction. A deterministic prediction error and a wave-shaping Wiener filter are used to transform the pulse train and reflections into a short symmetrical pulse. Additional broadening of the pulse spectrum is achieved by stacking of seismograms from shots with various dominant frequencies after zero-phase transformation of downgoing waves. The inversion of seismograms is made after ideal spiking by means of a subtraction procedure. Acoustic impedances deduced are closely related to lithology of rocks below bottom-of-hole.     

The use of the fractal dimension to quantify the morphology of irregular-shaped particles

For several decades, sedimentologists have had difficulty in obtaining an efficient index of particle form that can be used to specify adequately irregular morphology of sedimentary particles. Mandelbrot has suggested the use of the fractal dimension as a single value estimate of form, in order to characterize morphologically closed loops of an irregular nature. The concept of fractal dimension derives from Richardson's unpublished suggestion that a stable linear relationship appears when the logarithm of the perimeter estimate of an irregular outline is plotted against the logarithm of the unit of measurement (step length). Decreases in step length result in an increase in perimeter by a constant weight (b) for particles whose morphological variations are the same at all measurement scales (self-similarity). The fractal dimension (D) equals 1.0-(b), where b is the slope coefficient of the best-fitting linear regression of the plot. The value of D lies between 1.0 and 2.0, with increasing values of D correlating with increasing irregularity of the outline. In practice, particle outline morphology is not always self-similar, such that two or possibly more fractal elements can occur for many outlines. Two fractal elements reflect the morphological difference between micro-scale edge textural effects (D₁) and macro-scale particle structural effects (D₂) generated by the presence of crenellate-edge morphology (re-entrants). Fractal calibration on a range of regular/irregular particle outline morphologies, plus examination of carbonate beach, pyroclastic and weathered quartz particles indicates that this type of analysis is best suited for morphological characterization of irregular and crenellate particles. In this respect, fractal analysis appears as the complementary analytical technique to harmonic form analysis in order to achieve an adequate specification of all types of particles on a continuum of irregular to regular morphology.     

High resolution electron microscopic studies on ferrosilite III

High resolution transmission electron microscopic (HRTEM) studies on ferrosilite (Fs) III confirmed the periodicity nine (p=9) of the tetrahedral chains in this silicate. Various chain periodicity faults (CPFs) have been observed and faults with “elfer” units (p′=11) dominate. CPFs with p′?9 were observed and are interpreted as pyroxene like slabs. Synthesis of Fs III under extended run duration demonstrated that Fs III actually is the stable phase in the system FeSiO₃ at high pressures and high temperatures. However, the stability fields of Fs III and orthoferrosilite might be separated by a narrow field of a FeSiO₃ polymorph with “elfer” single chain. This field has not been bracketed so far. New structure variants of Fs are discussed. Reconnaissance experiments on the kinetics of CPFs are reported.     

Quantitative estimation of groundwater potentiality and rainfall infiltration in a typical crystalline environment

A sophisticated method of measuring water levels is adopted to determine the groundwater potentialities in a typical weathered and fractured environment by storage method. The frequency of the rainfall has shown a direct bearing on recharging the groundwater system compared to the intensity of the rainfall. The Thiessen polygon method is used to determine the weighted average of the rainfall over the basin area to estimate the ground water infiltration rates. The long term average infiltration to the medium is established as 15% of the total rainfall.     

Earthquake data analysis: An example from Sweden

Methods and results of earthquake data analysis are illustrated by the seismicity of Sweden in the period 1951–1976, summarizing a comprehensive research project for the past five years. Starting from the regional structural properties, methods are given for the evaluation of instrumental and macroseismic observations, including error analysis and source identification. The resulting earthquake distribution is investigated in relation to space (various types of seismicity mapping), time (periodicities) and magnitude (frequency-magnitude and energy-magnitude relations). The tectonophysical explanations of the earthquake origin are still subject to considerable uncertainty and can be treated only by way of discussions. The engineering applications, stimulated recently by the nuclear power industry, can be placed on much more reliable ground. They include calculations of seismic risk and fracture risk as well as investigations of certain phenomena of practical consequences, especially rockbursts.This review is primarily addressed to those who have use for seismological data in their work, especially geologists, tectonophysicists and engineers. It is important for them to realize how the seismological data are obtained, their reliability and their range of application. Sweden is here mainly used as an example, but the developed methods have a general applicability to any earthquake region, with proper modifications.In short, our purpose is two-fold: (1) to summarize recent research on the seismicity of Sweden: (2) to introduce all users of seismological data into methods and results.     

Embedding reach-scale fluvial dynamics within the CAESAR cellular automaton landscape evolution model

We introduce a new computational model designed to simulate and investigate reach-scale alluvial dynamics within a landscape evolution model. The model is based on the cellular automaton concept, whereby the continued iteration of a series of local process ‘rules’ governs the behaviour of the entire system. The model is a modified version of the CAESAR landscape evolution model, which applies a suite of physically based rules to simulate the entrainment, transport and deposition of sediments. The CAESAR model has been altered to improve the representation of hydraulic and geomorphic processes in an alluvial environment. In-channel and overbank flow, sediment entrainment and deposition, suspended load and bed load transport, lateral erosion and bank failure have all been represented as local cellular automaton rules. Although these rules are relatively simple and straightforward, their combined and repeatedly iterated effect is such that complex, non-linear geomorphological response can be simulated within the model. Examples of such larger-scale, emergent responses include channel incision and aggradation, terrace formation, channel migration and river meandering, formation of meander cutoffs, and transitions between braided and single-thread channel patterns. In the current study, the model is illustrated on a reach of the River Teifi, near Lampeter, Wales, UK.