Determination of Lithospheric Structure and Evolution from Seismic Refraction and Reflection Techniques: Studies of the Southern Rio Grande Rift and Tokai Region of the Nankai Trough, Japan

This dissertation consists of four research topics, addressing three different scales of crustal-scale seismic data analysis. At the large scale, this research involves determining the lithospheric crustal structure across the southern Rio Grande rift (SRGR) from a 205 km long refraction/wide-angle reflection profile across southern New Mexico into Far West Texas acquired during the Portillo Volcanic Field (PVF) seismic experiment in 2003. Analysis of this data will include first arrival tomography and ray tracing methods to determine the velocity structure integrated with gravity modeling to constrain the density structure. A smaller-scale analysis will be performed on two separate near-vertical reflection seismic data profiles. The first data set was acquired as part of the PVF experiment, consisting of an approximately 50 km long section with 100 to 200 m spaced receivers centered on the Potrillo Volcanic Field. This data was designed to provide a structural image and constrain the crustal properties underlying the PVF. The second data set consists of an approximately 50 km long profile with nominal 50 m spacing acquired as a piggy-back deployment to the Tokai experiment across the Tokai region of Japan in 2001. This data was designed to image the down-going Philippine Sea plate as well as to constrain the physical properties associated with the seismogenic zone associated with its subduction. Data analysis for both of these data sets will include reflection-processing techniques to develop a more detailed seismic image as well as amplitude, polarity and finite difference modeling to constrain physical characteristics of reflected interfaces. At the finest scale of data analysis, this research will involve modification of the tomography code used for velocity modeling. This will involve collaboration with the Computer Science department to modify the currently used tomography code developed by John Hole (1992). Modifications include changing the existing inverse algorithm to allow for interval uncertainties and weighted distribution of slowness perturbations determined from first arrival travel-time residuals.