Mechanics of fault-related folds and critical taper wedges
By: by Chris Anthony Guzofski
Published: 2007
Language: eng
Number of pages: 121
Description: We study the three-dimensional (3D) mechanics of crustal deformation, by investigating compressive systems at local and regional scales. In chapter 1, we constrain the subsurface geometry and seismotectonics of the Coalinga anticline, California. The 1983 Coalinga (M W = 6.5) earthquake is one of the most comprehensive examples of a blind thrust earthquake associated with a fault-related fold. Our model of the Coalinga anticline demonstrates that it is comprised of a series of imbricated structural wedges that are related to two master fault ramps at depth. We use relocated earthquakes to document the patterns of seismicity relative to our structural interpretation and the fault ramp that ruptured during the 1983 event. This analysis demonstrates that the majority of aftershock moment release occurred within the wedge and provides insights into the kinematic and mechanical processes that govern co-seismic blind thrust fault-related folding. In chapter 2 we investigate the mechanics of fault-related folding in two classes of structures---detachment and shear fault-bend folds---where strength heterogeneity significantly influences their deformation. Using 3D seismic reflection data, we construct models of natural growth fault-related folds that we sequentially restore using a new, finite element-based, volumetric structural restoration technique. The results provide full 3D restorations of complex structures which closely match two-dimensional kinematic theories and are used to quantify the influence of mechanical stratigraphy and bedding plane slip surfaces in folding. In chapter 3 we investigate the mechanics of two fold and thrust belts using a 3D implementation of critical taper wedge mechanics. With this method, we use the 3D shape of the fold and thrust belts to invert for wedge strength.

Our results demonstrate that both wedges have weak detachments due to elevated basal fluid pressures, leading to their low taper shapes. In each system, we compare the calculated mechanical parameters to the spatial distributions of various styles of thrusting and fault-related folding. We find that where the detachment is calculated to be weak, widely spaced shear fault-bend folds and shale ridges occur. Alternatively, regions of relatively high detachment strength correspond to ramps in the detachment and closely spaced, imbricated fault-related folds.
Notes: Thesis (Ph.D., Dept. of Earth and Planetary Sciences)--Harvard University, 2007.

Includes bibliographical references.