Date of Completion
Dr. Jean Crespi, Dr. William Ouimet
Field of Study
Master of Science
Traditional models of orogenic growth over-simplify the processes involved in the development of fold-and-thrust belts by failing to take into consideration along-strike irregularities of the collisional footwall. Inherited footwall geometries are fairly common and can drastically alter the shape of an advancing orogen during collision. In Taiwan, the geometry of the Chinese continental margin has been suggested to facilitate the development of several cross-structures, transverse structures that trend oblique to the structural grain of the orogen, within the fold-and-thrust belt. These cross-structures are believed to accommodate deformation around a regional footwall promontory, the Peikang High. In total, six major tear fault zones have been identified in previous studies, though their interpretations are almost exclusively derived from surface deformation studies. For this study, a catalog of earthquake seismicity and earthquake focal mechanisms were used to evaluate and characterize the cross-structures at depth. Using the Gauss inversion method, best-fit stress tensors were derived for each study area and the associated preferred nodal planes of failure were extracted for spatial analyses. Results suggest that deformation patterns north and south of the crustal promontory are characterized by systems of conjugate faulting that facilitate brittle extrusion of foreland material as the orogen becomes caught up in collision with the irregular margin. The region around the promontory represents a narrow zone of southward propagating, en echelon tear faults that accommodate differential displacement of the advancing thrust sheets through time. Tear faulting is limited to the upper crustal layers and are necessary for the orogen to advance over the promontory.
Lamont, Ellen A., "Cross-Structures and their Role in the Development of the Taiwan Fold-and-Thrust Belt" (2014). Master's Theses. 633.
Dr. Timothy Byrne