The University of Melbourne
School of Earth Sciences

A Cover Page for the subject

SEISMIC EXPLORATION

625393

Lindsay Thomas

This page summarises the subject, and contains pointers to some background material. As the subject is being given for the last time in 1997, it may not be updated in this format, but if interest is shown I may maintain it in some way in the future.

The text below is taken from the opening page of the subject notes (47 pages), which can be downloaded in .pdf format here. However, a password is needed to open the file. For the present that password is freely available if you would like to email me with your name, address, and interest; this will let me gauge whether further development is warranted. A lab manual may also become available later.

The recommended textbook is Applied Geophysics, by Telford, Geldart and Sheriff (1990) but material has been drawn from many sources. A list of references is given in the final section of the subject notes. Few journal references are included, basically through lack of preparation, but the textbooks cited give many references to earlier workand the Cumulative Index of Geophysics (SEG) is inexpensive!

These notes are intended as a lecture guide and minimal reference only, not as a textbook in the subject. This edition (1997) is a new-subject draft, which I would normally hope to be improved with feedback from the users. Accordingly, any general comments, or identification of particular errors, will be welcomed. The synopsis below outlines the topics which I will attempt to mention, at least. This should not be taken as a complete coverage of the field; there are some very notable omissions, and coverage of many other areas is necessarily superficial, given the time constraints.


The first part of the subject will discuss some elastic wave theory, leading to the idea of wavefronts propagating through elastic media. Subsequently we look at the progress of implicitly impulsive disturbances through (usually) layered media, and derive simple expressions for the travel times of rays which have been refracted or reflected at subsurface boundaries. Some complicating factors will be described briefly, as will be the general kinds of recording systems used.


We will then proceed to look at the result of using more realistic descriptions of the progressing wave, and at ways of overcoming the blurring that this leads to, particularly in the case of reflection seismology. Finally we will look briefly at some of the approaches to the interpretation of seismic sections.


Virtually all of the concepts to be discussed (there is one significant exception) were proposed and understood before about 1980. This is not to be read is implying that the content is outdated, nor that there has been no progress since then. Rather, the progress (especially in reflection seismology) has come through developing the basic ideas further, with the aid of computing capability, to overcome or at least subvert the difficulties posed by working in real physical field conditions. Each step forward in seismic exploration capability brings with it a new horizon; just as distant, but just as rewarding.

Synopsis

ELASTIC WAVE THEORY Stress-Strain Relationships Wave Motion Acoustic Impedance Interface Phenomena Vertical Incidence General Case Finite Reflector size Diffractions Seismic Waves Curved Wave Fronts Anisotropy (Aeolotropy ) Inhomogeneity Anelasticity SEISMIC SYSTEMS I Basic Requirements Sources Source Specification Detectors Field Layouts Recording System REFRACTION SEISMOLOGY Plane Boundaries Multiple Layers Hidden Layer / Blind Zone Continuous Velocity Variation Elevation Corrections Dipping Interface Irregular Boundaries Delay-Time Analyses Generalised Reciprocal Method Wavefront Methods Ray Tracing Time Term Analysis SEISMIC SYSTEMS II Reflection Profiling Velocity Spreads

REFLECTION SEISMOLOGY REFLECTIONS FROM A PLANE INTERFACE Horizontal Reflectors Dipping Reflector VELOCITY ANALYSES Direct Determinations Velocity Analysis of reflection data Velocity Functions Physical Factors affecting Velocities SEISMIC SYSTEMS III Digital Data Acquisition SIMPLE DATA PROCESSING Simple Digital Response Modelling AMPLITUDES Path effects Effects at reflectors DIGITAL DATA PROCESSING Correlation Filters "DECONVOLUTION" (in the seismic sense) Frequency Filtering Velocity Filtering t -p transform process Display Techniques Attribute Analysis 3D Techniques MIGRATION   Diffraction  Migration   Automatic Migration SEISMIC REFLECTION INTERPRETATION Basic Concepts   Appendix A Fourier Transform Applications   Appendix B REFERENCES

Background Material

A Powerpoint presentation (in .pdf format) given in a related subject at Monash University can be downloaded here. The main content of the presentation is an introduction to seismic sampling, convolution, deconvolution, and correlation. Email me for the password if you are interested in this file.

Links to related WWW material can be found here.

 

Provenance page (summarising all of the address and age details).