Best Problem Solving Approach by using Geophysics.
Problem Solving Approach using Geophysics
Geophysics can play an important role in helping solve resource exploration, environmental, or geotechnical problems. One has to bear in mind that geophysics measures contrast in physical properties like resistivity, density, hardness, magnetism etc. The application of geophysics is most effectively carried out by following a systematic approach. Careful thought and due diligence at each step is important to achieve a final outcome. The systematic approach consists of following steps:
Establish the geoscience objectives, consider conventional practice, and identify how geophysics might contribute. This could include:
� Mapping geology
� Locating buried objects
� Obtaining 3D images of the subsurface
Assemble prior information that might be relevant. Details for using the systematic approach will depend upon what information is being sought and what is available.
More often than not a geophysical method having yielded good results in a particular case, is applied to another case with a different geology. This needs to be avoided. The problem needs to be defined elaborately, enabling geophysicists to decide on suitable approach to handle the problem.
Understand how geologic and man-made materials of relevance to the problem can be characterized by physical properties. The key is to find a physical property of the sought object/geology that is different from that of the surrounding material. This is a crucial component needed to link geophysics with the geoscience problem being investigated. Important physical properties are:
� Compressional wave and shear wave velocities
� Magnetic susceptibility
� Electrical conductivity (or resistivity)
� Electrical chargeability
� Dielectric permittivity
Field Surveys/ Data Acquisition:
Select a geophysical survey that is sensitive to the physical property of relevance to the problem. Design an effective and efficient methodology for collecting the field data. This will involve forward modelling and processing of the simulated data as well as addressing issues of noise and data quality. This builds realistic expectations for what information can be expected from analysis of the geophysical data and the overall suitability of the chosen survey.
Avoid using a single method to solve the problem. Two entirely different material can have similar physical property. As an example saturated gravels (clean), saturated gravels (dirty), clay deposits, weathered rock, coal and quick sand are likely to give a P wave velocity of 1500 m/s and cannot be differentiated unless shear wave measurements are made. Another example is a soft formation not getting detected under hard rock using seismic refraction alone. It is therefore always advisable to use a combination of suitable geophysical methods to uniquely solve the problem.
Carry out the field survey taking all necessary actions to ensure complete, high quality, and cost effective data sets. Geophysical data can be acquired in boreholes, on the surface, or in the air using aircraft. Field procedures must permit acquisition of high quality data, yet they must be economical, and safe to obtain.
There is no substitute to a good quality data obtained while in field. Data processing steps can only work to aid in data interpretation, but can never turn a bad data into good.
Interpretations from the data require that the data be processed. This can range from simply making maps of the data to inverting data to obtain 3D images of the subsurface.
Data processing should be done carefully with focus on improving interpretability of data rather than trying to make it look good. Over processing must be avoided and care must be taken to avoid artefacts.
Interpret results in terms of geological or geotechnical objectives. The goal is to draw conclusions or make decisions based upon the geophysical data. There are two distinct components to interpretation. The first involves estimating how physical properties are distributed. The second involves gaining some geological understanding based upon those physical property distributions. Just like much of the geosciences, non-uniqueness is a ubiquitous and persistent characteristic of most geophysical interpretations.
Correlate the interpretations 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, and their impact upon the initial geological, engineering, or geophysical question.
All tasks in the seven-step process 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 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.
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