On the detection of shallow objects using seismic wave reflections


Papandreou, B. (2011) On the detection of shallow objects using seismic wave reflections. University of Southampton, Faculty of Engineering and the Environment, Doctoral Thesis , 207pp.

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Description/Abstract

This thesis is concerned with a methodology for the detection of shallow (of order 1 metre) objects buried in soil using seismic waves. Possible objects of interest include infrastructure, archaeological artefacts and ordinance. A mathematical analysis of an idealised system is performed to gain understanding of both seismic wave propagation and the generation of these waves by surface sources. The mathematical techniques used in the existing analysis of a point vertical source are applied to the desired problem of a point horizontal surface traction. Results are displayed in a graphically concise form. An experimental methodology, capable of forming two-dimensional images through the ground, is described. The use of shear waves is shown preferable. The advantages and implementation of using time extended, rather than impulsive, excitation signals are described. Additional signal processing techniques, such as generalised cross-correlation functions, are also detailed. Simple numerical simulations are undertaken with the aim of both validating the post-processing algorithms and evaluating its robustness against non-ideal conditions. Simulated time histories are created by defining signals in the frequency domain and then modifying their amplitude and phase to replicate attenuation and propagation. Non-ideal conditions focus mainly on variation in the wavespeed as a function of depth. Simulations indicate that the imaging method fails for sufficiently large variations of wavespeed, particularly for objects buried below significant discontinuities in material properties. As shear waves are used for the imaging method, a source was designed and constructed to preferentially generate shear waves and was verified using field experimentation. The imaging methodology is applied to data from three experimental sites and is able to detect the target objects with some success. Problems, however, remain with the measurement of a wavespeed that is consistent and indicative of the propagation speed at depth, and in consistently obtaining a sufficiently large reflected wave from the object.

Item Type: Thesis (Doctoral)
Subjects: C Auxiliary Sciences of History > CC Archaeology
Q Science > QC Physics
T Technology > TA Engineering (General). Civil engineering (General)
Divisions: Faculty of Engineering and the Environment > Institute of Sound and Vibration Research
ePrint ID: 334160
Date Deposited: 28 Jun 2012 10:00
Last Modified: 27 Mar 2014 20:19
URI: http://eprints.soton.ac.uk/id/eprint/334160

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