Tom Wilson, Department of Geology and Geography Environmental and Exploration Geophysics II tom.h.wilson Department of Geology and Geography West Virginia University Morgantown, WV Summary of Pitfall Lab Exercises

Tom Wilson, Department of Geology and Geography Today we’ll talk about frequency, bandwidth and their relationship to resolution Computer exercise centered around evaluating the resolution limits in your data sets Attribute analysis with computer lab centered on potential applications to your project data A brief review of ground penetrating radar methods (read pages 524 to 528 in Burger et al.).

Tom Wilson, Department of Geology and Geography The glacial valley (“syncline”) we hoped to build In this case we think we know the geology and we’re trying to get an idea of what the geology will look like.

Tom Wilson, Department of Geology and Geography Raytrace plot showing overlapping rays from two horizons Forward modeling through ray tracing

Tom Wilson, Department of Geology and Geography Corresponding time plot – can you explain what you see? Burried focus event - reverse branch … & also known as a “bow-tie”

Tom Wilson, Department of Geology and Geography Look at what happens to the raypaths that reflect from the underlying flat layer The overlying layer of low velocity material acts like a lense that refracts the rays from the underlying layer. A combination of velocity and geometrical pitfalls.

Tom Wilson, Department of Geology and Geography 2000fps fps 20000fps fps The static anomaly that arises from near-surface low velocity zones that have not been considered or detected in the processing.

Tom Wilson, Department of Geology and Geography The apparent structure that you see in the deeper layer is all spurious and may mislead the interpreter.

Tom Wilson, Department of Geology and Geography An erroneous view of the subsurface may result The static anomaly

Tom Wilson, Department of Geology and Geography This model is used to dissect the issues discussed in “Pitfalls” associated with the serendipity reef The structural model

Tom Wilson, Department of Geology and Geography The irregular velocity distributions associated with this unique geological environment produce a different type of lensing and arrival time distortions

Tom Wilson, Department of Geology and Geography Velocity and geometry reduce travel times in some areas and reflect and refract acoustic waves resulting in a distorted view of the subsurface

Tom Wilson, Department of Geology and Geography This is a generalized model of complex structure located just north of Morgantown in the Summit field along the Chestnut Ridge anticline.

Tom Wilson, Department of Geology and Geography Structural geometry of the area scatters and refracts raypaths in a variety of directions to produce a deceptively simple time section

Tom Wilson, Department of Geology and Geography Broadened response from the anticline Reverse branch or buried focus event Apparent structure in the underlying flat layer

Tom Wilson, Department of Geology and Geography Processors do an excellent job of eliminating a lot of these geometrical and velocity distortions, but in both cases, a necessary requirement is to have accurate velocity control and that can be lacking even in areas where you have well control. These possibilities are worth being aware of and keeping at the forefront when you are interpreting features you see in time and depth converted views.