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Receiver Locations (receiver + locations)

Distribution by Scientific Domains

Engineering	50%
Earth and Environmental Science	50%

Selected Abstracts

Guided waves at subduction zones: dependencies on slab geometry, receiver locations and earthquake sources

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2006
S. Martin
SUMMARY We investigate the geometry of deep subduction zone waveguides (depth >100 km). The wavefield characteristics for up-dip profiles are described and compared with data recorded at the Chile,Peru subduction zone. Observed distorted P onsets at stations in northern Chile near 21°S can be matched by 2-D finite difference simulations of a thin low-velocity layer (LVL) atop the slab in an IASP91 velocity model. The replacement of the LVL by simple random velocity undulations in the slab in the same model cannot explain the observations. Varying slab geometries are investigated and the distribution of guided wave onsets originating in deep waveguides is predicted relative to the slab surface. Further, double couple source position and orientation is explored and found to be closely limited by the guided wave observations. Sources situated above the layer and at distances more than 2 layer widths below the subducted Moho are not suitable. For the remaining favourable source locations, a strong link between pulse shapes and fault plane dip angle is evident. We conclude that up-dip guided wave observations at subduction zones follow a simple pattern given by slab geometry and modified by source position. The resulting onsets are shaped by layer thickness and velocity contrast and further influenced by the shape of the slab surface. [source]

Time-varying time-shift correction by quasi-elastic deformation of seismic traces

GEOPHYSICAL PROSPECTING, Issue 2 2000
Masjukov
Residual static correction is based on a model of time shifts (delays) that depend solely on source and receiver locations at the surface. This assumption is valid if all raypaths are vertical in the near-surface layering. We consider a more general model of the time-varying time shifts that remain after hyperbolic NMO correction (of non-hyperbolic trajectories) and static correction. We assume that the wavelet distortion caused by the time-varying shifts is smooth. We have developed an algorithm for its correction (phase correction), based on minimization of the target functional with a penalty term similar to the quasi-elastic energy of the time-axis deformation. The use of a mechanical analogy for optimization is well known (e.g. simulated annealing). We propose here a stable numerical method that deals with a pair of seismic traces. It may be applied to phase correction of CMP (or CDP) gathers and stacked sections. Synthetic and field examples confirm that our method appreciably increases the signal-to-noise ratio, and improves the coherence and resolution. [source]

Wave propagation velocity under a vertically vibrated surface foundation

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2009
Jaehun Ahn
Abstract The ultimate objective of the research conducted by the authors is to explore the feasibility of determining reliable in situ values of soil modulus as a function of strain. In field experiments, an excitation is applied on the ground surface using large-scale shakers, and the response of the soil deposit is recorded through receivers embedded in the soil. The focus of this paper is on the simulation and observation of signals that would be recorded at the receiver locations under idealized conditions to provide guidelines on the interpretation of the field measurements. Discrete models are used to reproduce one-dimensional and three-dimensional geometries. When the first times of arrival are detected by receivers under the vertical impulse, they coincide with the arrival of the P wave; therefore related to the constrained modulus of the material. If one considers, on the other hand, phase differences between the motions at two receivers, the picture is far more complicated and one would obtain propagation velocities, function of frequency and measuring location, which do not correspond to either the constrained modulus or Young's modulus. It is necessary then to conduct more rigorous and complicated analyses in order to interpret the data. This paper discusses and illustrates these points. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Signal enhancement in multiuser communication through adaptivity on transmit

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2003
Abdellatif Medouri
Abstract This paper presents a technique to enhance the received signals in a multiuser communication environment through the use of adaptivity on transmit. This technique is based on the principle of reciprocity and is independent of the material medium of transmission and the near-field environments. The objective here is to select a set of weights to be applied to each transmitting antenna, which is a function of the user location. The methodology is not a function of the multipath environment. Furthermore, the transmitted signal may be directed to a particular receiver location and simultaneously be minimized at other receiver locations while operating on the same frequency. Numerical simulations have been made to illustrate the novelty of the proposed approach. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 265,269, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11034 [source]