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Geophysics foundations:  
Applying geophysics; a 7-step framework


 

What's down there?A general seven-step framework for using applied geophysics

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.

On the remainder of this page, the framework is summarized three different ways - first in a short table, then graphically, and finally in a table with a few more discussion details. Note that there is a FlashTM-based, interactive multimedia module in "Resources", which introduces this generally applicable seven-step framework for applying geophysics.

Summary table for the seven-step framework:
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 framework visually:

1. Setup

2. Properties
3. Surveys
 gathering data in the field
4. Data
raw data

7. Synthesis

- Integration of geophysics with all other
   knowledge about the project.
- Do results correlate with prior and
   alternative information?
- Is the outcome adequate for the project?
- Iteration back to previous steps is
   expected  before finalizing the work.

6. Interpretation
5. Processing
model produced by inverting data

A few more details for each of the seven steps are outlined in the following table. Some terminology may need to be looked up in the glossary:

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.
- Locating buried objects
- 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:
Carry out 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 are 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 is 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.