Fault structures and their geoelectric parameters in the epicentral zone of the 27 September 2003 Chuya earthquake (Gorny Altai) from resistivity data

This paper presents an integrated measurement technique based on DC methods (vertical electrical sounding, electrical resistivity tomography) which was used to identify faults and determine their geoelectric parameters in the western part of the Chuya basin. New information on the structure of the Chagan River valley located in the zone of the disastrous 27 September 2003 Chuya earthquake has been obtained from the results of these methods. Geoelectric cross-sections of the sedimentary sequence and the upper part of the basement were obtained from VES data, showing the block structure of the study area. Electrical resistivity tomography sections confirm the presence of a major fault between basement blocks of different heights and indicate the presence of faults bounding the valley on its right side and in the southwestern part.     

Engineering problems associated with expansive clays from Romania

Engineering problems associated with expansive clay formations, which have a large swelling and shrinking potential, exist in different regions of Romania.In the general framework of the study of the behaviour of expansive clays, the present paper describes some particular aspects connected with the swelling and shrinkage processes and their engineering effects in Romania.The differences between swelling potential relationships, obtained by two different methods are presented and discussed. Swelling pressure tests were accomplished using the available standard techniques, as well as a specially developed cell pressure equipment.Attention is drawn to the stages of the shrinkage process as related to soil structure. It was found that, in a general case, there are three distinct?tages: initial, normal and residual shrinkage.Laboratory investigations have shown that in soils with an anisotropic structure, the directional variation of shrinkage strains is elliptical in shape, with the maximum shrinkage normal to particle orientation.The engineering aspects of the results are discussed.     

Dynamical studies of cluster pairs in the Magellanic Clouds

We performed N -body simulations of star cluster encounters with Hernquist's TREECODE in a CRAY YMP-2E computer under different initial conditions (relative positions and velocities, cluster sizes, masses and concentration degrees). The total number of particles per simulation ranged from 1024 to 20480. These models are compared with a series of isodensity maps of cluster pairs in the Magellanic Clouds. Evidence is found that during the interactions, transient morphological effects such as an expanded halo, isophotal deformation and isophotal twisting can occur as a result of tidal effects and dynamical friction. The simulations also show that different outcomes are possible depending on the initial parameters: (i) long-standing changes of concentration degree can occur after the collision; (ii) one member can disaggregate; or (iii) the pair can coalesce into a single cluster with a distinct structure compared with the original ones. These simulations can reproduce a wide range of morphological structures in observed cluster pairs.     

THE THIN-LAYER PROBLEM IN GEOELECTRICAL PROSPECTING *

For a thin highly-conducting layer with given longitudinal conductance the recurrence formulae for an n-fold horizontally stratified subsoil are established for d.c. resistivity and magnetotelluric soundings. Similarly, a thin low conductivity layer with given transverse resistance is treated in the d.c. case and a non-conducting intermediate bed in magnetotellurics. Model curves for a thin high- or low-conductivity intermediate layer in the three-layer case have been carried out, which may serve as an extension of the well-known three-layer diagrams for a Schlumberger configuration. The corresponding model curves in magnetotellurics are given. By numerical comparison of these curves with real three-layer curves some diagrams have been developed to show the allowed thicknesses of the intermediate layer in the Schlumberger case and in the case of magnetotelluric sounding.