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Homogeneous Half-space (homogeneous + half-space)

Distribution by Scientific Domains

Earth and Environmental Science	75%

Selected Abstracts

The effect of foundation embedment on inelastic response of structures

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2009
Mojtaba Mahsuli
Abstract In this research, a parametric study is carried out on the effect of soil,structure interaction on the ductility and strength demand of buildings with embedded foundation. Both kinematic interaction (KI) and inertial interaction effects are considered. The sub-structure method is used in which the structure is modeled by a simplified single degree of freedom system with idealized bilinear behavior. Besides, the soil sub-structure is considered as a homogeneous half-space and is modeled by a discrete model based on the concept of cone models. The foundation is modeled as a rigid cylinder embedded in the soil with different embedment ratios. The soil,structure system is then analyzed subjected to a suit of 24 selected accelerograms recorded on alluvium deposits. An extensive parametric study is performed for a wide range of the introduced non-dimensional key parameters, which control the problem. It is concluded that foundation embedment may increase the structural demands for slender buildings especially for the case of relatively soft soils. However, the increase in ductility demands may not be significant for shallow foundations with embedment depth to radius of foundation ratios up to one. Comparing the results with and without inclusion of KI reveals that the rocking input motion due to KI plays the main role in this phenomenon. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Absolute S -velocity estimation from receiver functions

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2007
L. Svenningsen
SUMMARY We present a novel method to recover absolute S velocities from receiver functions. For a homogeneous half-space the S velocity can be calculated from the horizontal slowness and the angle of surface particle motion for an incident P wave. Generally, the calculated S velocity is an apparent half-space value which depends on model inhomogeneity and P -waveform. We therefore, suggest to calculate such apparent half-space S velocities from low-pass filtered (smoothed) receiver functions using a suite of filter-parameters, T. The use of receiver functions neutralize the influence of the P -waveform, and the successive low-pass filterings emphasize the variation of S velocity with depth. We apply this VS,app.(T) technique to teleseismic data from three stations: FUR, BFO and SUM, situated on thick sediments, bedrock and the Greenland ice cap, respectively. The observed VS,app.(T) curves indicate the absolute S velocities from the near surface to the uppermost mantle beneath each station, clearly revealing the different geological environments. Application of linearized, iterative inversion quantify these observations into VS(z) models, practically independent of the S -velocity starting model. The obtained models show high consistency with independent geoscientific results. These cases provide also a general validation of the VS,app.(T) method. We propose the computation of VS,app.(T) curves for individual three-component broad-band stations, both for direct indication of the S velocities and for inverse modelling. [source]

Numerical modelling of complex resistivity effects on a homogenous half-space at low frequencies

GEOPHYSICAL PROSPECTING, Issue 3 2006
T. Ingeman-Nielsen
ABSTRACT The many different existing models describing the spectral behaviour of the resistivity of geological materials at low frequency, combined with the lack of available field data, render the interpretation of complex resistivity (CR) data very difficult. With a recent interest in CR-measurements for environmental applications and thanks to technological progress, the use of wide-band frequency equipment seems promising, and it is expected to shed light on the different results among the published solutions to the electromagnetic (EM) coupling problem. We review the theory of EM-coupling over a homogeneous half-space with CR-effects and study some aspects of the complex coupling function. We advocate the use of the CR-based coupling function in the interpretation process, in order to obtain a better understanding of the physical processes involved in CR-effects. Application of the model to real field data shows systematic good agreement in two simple cases, even over wide ranges of frequencies. Interpretation with a double Cole,Cole model is applied for comparison, and in spite of good fits to the data, large differences are observed in the interpreted low-frequency dispersion. We conclude that the use of a second Cole,Cole model to describe EM-coupling may corrupt the interpretation of the low-frequency dispersion, even when only the normal range of frequencies (<100 Hz) is considered, and that the use of the actual EM-coupling expression is essential when the goal is a better understanding of interaction between CR-effects and EM-coupling. [source]

Distortions of EM transients in coincident loops at short time-delays

GEOPHYSICAL PROSPECTING, Issue 6 2000
F. Kamenetsky
Transient electromagnetic measurements with short time-delays of transients are used for solving different problems within the upper part of a geoelectric section. However, it is necessary to take into consideration distortions connected with self-transients within the transmitter,receiver system. From the practical point of view, it is important to estimate the minimum time-delay after which these distortions may be neglected. We present such an estimation which uses a simple approximation method for a single-loop (or coincident-loop) configuration. For common values of the loop size (10 m × 10 m to 40 m × 40 m) and of the resistivity of a homogeneous half-space (1,100 ,m), the minimum time-delay beyond which we can use a standard interpretation is in the range of 2,10 µs. This is equivalent to a minimum depth of investigation in the range of 1,30 m. [source]