Steven Lingrey, 1991. "Seismic Modeling of an Imbricate Thrust Structure from the Foothills of the Canadian Rocky Mountains", Seismic Modeling of Geologic Structures: Applications to Exploration Problems, Stuart W. Fagin
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Seismic structural modeling provides a useful means toward understanding the complex geometry associated with detached-style fold and thrust deformation. Routine seismic methods do not tightly constrain details of structural interpretation, but methods incorporating geometric and seismic modeling allow these details to be inferred. Geometric models measure spatial elements of the folds and faults, and check them for internal consistency, usually against an assumed condition of material balance. Seismic models measure the effects of ray-path bending through a complex, structurally defined velocity field. The seismic model predicts the presence (or absence) of reflections and their pattern on unmigrated sections. These patterns in the modeled data can be checked against the patterns observed in the real data. Iteration between the two models allows the interpretation to converge toward a mutually acceptable solution.
Structural analysis of a seismic profile across the Quirk Creek gas field from the Foothills belt of the Canadian Rocky Mountains is used to illustrate this iterative method of seismic interpretation. The internal geometry of thrust sheets, essentially opaque on the basis of routine examination of a migrated seismic profile, is developed with the aid of geometric and seismic modeling techniques. As with many model-based approaches, proposed solutions in a given geometric or seismic model are nonunique. Used in combination, however, they each check solutions independently and thus can more narrowly constrain the range of acceptable interpretations. The incorporation of synthetic seismic modeling greatly improves the accuracy of interpretation for the structurally complicated Quirk Creek gas field.
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Seismic interpretation apparently is becoming primarily a geologic rather than a geophysical skill. This observation has been true from the moment seismic reflection data were displayed as a continuous record with the intention of creating an image of subsurface structure. The imaging advances that have occurred in the past two decades only reinforce the tendency. More effective migration algorithms making use of faster and less expensive computers, as well as high-fold and, in particular, 3-D data all serve to make the seismic picture better. As the image increasingly reveals more geology, the geologic skills become more crucial to the task of extracting the information made available. As seismic artifacts such as multiples, sideswipe, and raypath distortion effects are successively eliminated from the image, the geophysical sophistication of the interpreter becomes increasingly less important. At first glance it would seem that these tendencies can only intensify as these technological trends continue.
And yet the depiction of complex structures remains elusive. Migration programs have been developed that can manage the severe raypath bending attendant with complex structures. Moreover, the ever decreasing costs of computation make the application of these programs increasingly more feasible. Unfortunately, to benefit from these imaging approaches requires, a priori, an increasingly more precise definition of the velocity field which often is, in itself, an expression of geologic structure. Therefore, before we can create the image, we require an understanding of what the image is supposed to show. This circumstance implies that the preparation of the seismic image has become, and will likely remain, inextricably bound up with its interpretation.