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3-D Seismic Expression of Karst Using 3-D Synthetic Seismic Model of Modern Analogs

Janson, Xavier 1; Fomel, Sergey 1
1 Bureau of Economic Geology, Jackson School of Geosciences, UT Austin, Austin, TX.

Karst terrains encompass a large range of geomorphologic expressions of multiple processes, such as carbonate dissolution, fracturation, sediment deposition, precipitation, and brecciation. The resulting diagenetic effect and geobodies range in size from several hundreds of meters (e.g., seismic scale) to centimeter scale (vug dissolution) or less.

Except for larger scale features such as sinkholes or karst towers, carbonate karst can be hard to detect on seismic data. We use the geomorphology of “modern” karst to explain the 3D seismic response of various karst terrains. The 3D modern karst morphologies such as such as caves, sink hole, cockpit karst, and karst tower were extracted from a high-resolution, satellite-derived DEM, 3D model of modern caves our ground-based lidar survey. Several impedance models were built for each karst morphology, one using a layered velocity model as a background and the other using a stochastic velocity model, with both models showing a significant velocity change at an upper surface corresponding to a major unconformity.

These synthetic models showed that dissolution and collapse features are subtly imaged by seismic data on vertical sections and are better seen on horizontal or stratigraphic slices. Karst dissolution features recognition mostly depends on the velocity (e.g., the nature) of the void filling. Kars topography at the unconformity usually creates significant seismic artifact that are key diagnostic features of karst modified platform top. These synthetic seismic models are strikingly akin to real subsurface examples.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009