HR: 1340h
AN: T43B-1341    [Abstracts]
TI: Growth of Fault-cored Anticlines by combined Mechanisms of Fault Slip and Buckling
AU: * Huang, W
EM: huang22@indiana.edu
AF: Department of Geology Sciences, Indiana University, 1001 E. 10th Street, Bloomington, IN 47408,
AU: Johnson, K M
EM: kajjohns@indiana.edu
AF: Department of Geology Sciences, Indiana University, 1001 E. 10th Street, Bloomington, IN 47408,
AB: A primary goal of studies of blind faults underlying actively growing anticlines is assessment of earthquake hazard associated with slip on the faults. It is generally assumed that the amount of slip on the fault is directly related to the amplitude of the fold. Under this assumption, the potential for earthquakes on blind faults can be determined directly from fold geometry. However, anticlines grow over slipping reverse faults can be amplified by a factor of two or more by buckling of mechanical layering under horizontal shortening. Studies that attempt to estimate fault slip from fold geometry may therefore overestimate fault slip by a factor of two or more if the contribution to fold growth from buckling is ignored. We construct boundary element models to demonstrate that fault-cored anticlines in mechanically layered media subjected to layer-parallel shortening are not built solely by slip on the underlying fault. The amplitude of folds produced in a medium containing a fault and elastic layers with free slip and subjected to layer-parallel shortening are 2-5 times larger than the amplitudes of folds produced in homogeneous media without mechanical layering. We compare the model results with data from fault-cored anticlines in the western United States. Pitchfork Anticline on the western flank of the Big Horn Basin in Wyoming likely formed by the combined mechanisms of fault slip and buckling. Geometric features of Pitchfork Anticline such as a localized anticlinal dome shape with tight hinges and amplitude that increases away from the fault tip are characteristic features of buckle folds produced in our numerical simulations. The coseismic uplift pattern produced during the 1985 earthquake on a fault under the Kettleman Hills Anticline and subsurface fold geometry of the anticline inferred from seismic reflection images are consistent with folding produced by the combined mechanisms of fault slip and buckling.
DE: 8005 Folds and folding
DE: 8036 Paleoseismology (7221)
DE: 8108 Continental tectonics: compressional
SC: Tectonophysics [T]
MN: 2007 Fall Meeting