I began my geoscience education in standard fashion, sketching line-drawings of outcrop bed geometries from road-cuts, scrubby creek bank-cuts, and the occasional quarry. Eventually the class moved on to exercises in stereographic aerial photography interpretation, again utilizing at its core simple lines on a page to represent geologic interpretation. The act of tracing lines on paper is almost insultingly literal, yet the geologic implications of the lines, the hypothesis that is laid bare, can be a thing of reasoned beauty.
Later I spent several seasons creating geologic maps from disparate pieces of spatial and temporal information, but looking back, I was just practicing how to meaningfully draw the lines. I was learning how to hypothesize within the constraints of the available evidence, guided by classical geologic reasoning. One summer I had a chance to work with 3D seismic data and things have never been the same. The amount of geologic information available in one place absolutely staggered me. I have been a proud seismic interpreter (a.k.a. geologist) ever since.
Philosophy and tips
Seismic reflection interpretation is one method of geologic interpretation. In order to get better at it you need to practice constructing and destructing testable geologic stories or hypotheses. Some may label this approach as ‘model driven’; I suggest geoscientists are required to drive a testable model to be debunked, improved, or expanded. You will need to grasp all the options and weigh their merits before being able to meaningfully assign risk or resource to your geologic assessments.
The following are a set of simple tips for crafting an interpretation from seismic reflection data:
- Obtain and integrate with your interpretation every piece of geologic information available.
- Remember, the top of a geologic package must have a bottom.
- Always look for and map packages of geometries, usually called sequences.
- Avoid mapping just one surface at a time.
- As you pick seismic markers, think about what those surfaces represent geologically.
- Is that bright marker you were drawn to a downlap feature, an unconformity, or just a bright marker that you can map on a few lines?
- What are the implications of your current pick for the upcoming strike line? What should you see if you are right with your current model?
- Visualize what the map will look like before hitting the Grid button.
- When working with 2D data, interpret between the lines. What are you predicting to exist between data points?
- If you don’t hold the working hypothesis in the forefront of your mind while interpreting then you are just an expensive autotracker; be a geologist.
The more familiar you become with interpreting while hypothesizing, the quicker you will be at calculating options and understanding as many geologic arguments fitting the data as possible. People may see this insight as a form of blind intuition, when in fact it is an attainable-through-practice science reasoning skill. Seek to habitually sharpen your geologic reasoning skills while interpreting. When done fluently, the results will be a clear and comprehensive understanding of the possible subsurface models, appropriately scaled to the available data quality and coverage.
Never forget to assess the confidence you have in the evidence that is feeding your hypothesis. With new data comes a recalibration of the geologic story, don’t be afraid to change. It is distressing, but sometimes interpretations need to die.