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Seven steps to applying geophysics for any geological or geotechnical
problem
Whether the problem involves characterizing a few cubic metres, or a
volume of ground hundreds of metres thick underlying tens of square kilometers,
the following seven steps invariably will be addressed at some point
in the project. All seven tasks are inter-related so the distinction
between the steps can become blurred. For example, the geoscience problem
will determine an appropriate interpretation procedure,
which in turn will place constraints upon the survey design
and choice of processing steps. Also, data processing, interpretation and synthesis are
often particularly tightly related. However it is useful to think in
terms of these seven steps because they form a framework which can be
employed for any application of geophysical work to applied geoscience
problems.
1. |
Setup: |
Establish the geoscience objectives, consider
conventional practice, and identify how geophysics might contribute. |
2. |
Properties: |
Characterize materials that can be expected
and establish the likely physical property contrasts. |
3. |
Surveys: |
Determine a suitable geophysical survey, and
design an effective and efficient field survey. Identify possible
sources of error, noise and mis-interpretation. |
4. |
Data: |
Carry out the field survey, taking all necessary
actions to ensure compelete, high quality, and cost effective
data sets. |
5. |
Processing: |
Plot the data, and apply appropriate processing
and analysis. |
6. |
Interpretation: |
Interpret results in terms of physical property
distributions, and then in terms of the original geoscience objectives. |
7. |
Synthesis: |
Combine interpretations with prior knowledge
about the problem, and with other relevant information. Decide
if your results are adequate for the particular problem. Iteration
is usually necessary. |
This sequence of images summarizes the process:
A
few more details for each of the seven steps are outlined in the following
table:
1. |
Setup:
|
Establish the geoscience objectives, consider
conventional practice, and identify how geophysics might contribute.
Details of setting up the problem depend upon which of the four general
task types is involved.
- Buried object location
- Mapping "apparent" physical properties
- Identifying boundaries where physical property values change
- Mapping detailed locations and depths of actual physical property
values |
2. |
Properties:
|
Characterize materials involved and establish
the likely physical property contrasts.
Understanding how physical properties relate to geophysical work is
crucial. The most important relevant physical properties are:
1. Density; 2. Compressional wave and shear wave velocities; 3.
Magnetic susceptibility; 4. Electrical conductivity (or
resistivity); 5. Electrical chargeability; 6.
Dielectric permittivity
|
3. |
Surveys:
|
Determine a suitable geophysical survey,
and design an effective and efficient field survey. Identify
possible sources of error, noise and mis-interpretation.
Successful application of geophysical techniques depends
upon careful survey design and data acquisition. Matching surveys
to suit the relevant physical properties is important, and forward
modelling may contribute towards building appropriate expectations
for data quality, noise levels, and suitablility to the task. |
4. |
Data:
|
Do the field survey taking all necessary
actions to ensure compelete, high quality, and cost effective
data sets.
Geophysical data can be gathered inside boreholes, using
ground-based systems, or from aircraft. Field procedures must
permit acquisition of high quality data, yet they must be economical,
safe, and reliable. |
5. |
Processing:
|
Plot the data, and apply appropriate processing
and analysis.
In nearly all cases interpretation can not proceed until
some form of data processing has been applied. This may be as
simple as a calibration, or it may involve multiple numerical
processing steps or data inversion. |
6. |
Interpretation:
|
Interpret results in terms of geological
or geotechnical objectives.
The goal of interpretation is to draw conclusions from the
geophysical data. Two types of conclusions were introduced, the
first being an understanding of physical property distributions,
and the second being a geological understanding derived from
models of physical property distributions.
Non-uniqueness was identified as a key characteristic of most geophysical
interpretations. |
7. |
Synthesis:
|
Correlate with prior and alternative information,
and decide if your results are adequate for the particular
problem.
Synthesis means making sure geophysical results agree with everything
else that is known about the problem. Also a judgement must be made
about the effectiveness and completeness of the geophysical results. |

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