published_or_final_version / Earth Sciences / Master / Master of Philosophy

The 2008 Wenchuan Ms 8.0 earthquake resulted in huge casualty and heavy strike to the local economy. Consequently, Chengdu Plain, with dense population and short distance to the highly active Longmen Shan fault zone needs an evaluation of the risk of earthquake as soon as possible. As part of a big project, we conducted mapping of gravity anomaly of Chengdu Plain in order to locate the possible buried fault zones beneath the Chengdu Plain. In this project a total of 640 km2 area was surveyed, and 230 relative gravity data have been collected along six profiles with each extending to about 70 km across the plain area. 140 more spots were measured around the city area in order to have a more precise delineation of geological structures beneath the city region. The Bouguer gravity anomaly has been calculated to delineate the large-scale anomaly trend on the surface. Data analyses presented that a coincidence between the sedimentation thickness and the residual gravity anomaly. The minimum residual anomalies suggested locations where depo-centers used to located (Pengzhou-Chongzhou, across Xinsheng County). The long-wave trend of Bouguer anomaly which reflects the deeply buried Moho discontinuity presented a northwest dipping trend of this density boundary underneath the plain region. / published_or_final_version / Earth Sciences / Master / Master of Philosophy

Not available / text

Not available / text

The Pioneer Mountains of Idaho expose a lower plate core of Precambrian and Ordovician metasedimentary rocks, which are intruded by Cretaceous and Eocene plutonic bodies. The core is separated by a detachment fault from a surrounding upper plate of Paleozoic and Tertiary sedimentary and volcanic units. The detachment system developed during a Tertiary extensional event which overprinted Paleozoic and Mesozoic east-directed compressional features, and exhibits both brittle and ductile (mylonitic) deformation. Stretching lineations in the mylonite and striations along the detachment surface both cluster around N65W. Composite planar fabrics (s- and c-surfaces) in the mylonite and limited development of a mylonitic front along the NW side of the core both suggest a top-to-the-west sense of shear. Minimum translation is estimated at about 17 km. The Pioneer structural complex is one of a number of metamorphic core complexes present along the North American Cordillera. All exhibit Tertiary extensional deformation, expressed as detachment faults structurally adjacent to ductile mylonitic shear zones. Extension directions, as indicated by stretching lineations within mylonite and striations along detachment faults, fall into regional groups in which the directions are similar in trend throughout each group. Asymmetric fabrics on both small and large scales give senses of shear and indicate that tectonic vergence within each group is directed outward from a central axis. The regional consistency of extension directions implies a regional control of extension in metamorphic core complexes. Much of central Idaho, and possibly a large part of eastern Idaho as well, may be riding on the upper part of an extensive detachment terrane, of which the Pioneer complex exposes the deeper levels. The Pioneer complex, and other core complexes, owes its present elevation to isostatic uplift over an overthickened crustal welt of local scale. Larger-scale uplift may be due to a similar isostatic adjustment over a broad zone of crustal thickening from Mesozoic compressional tectonics and intrusion.

published_or_final_version / toc / Applied Geosciences / Master / Master of Science

No description available.

No description available.

No description available.

No description available.