Dissertation Defenses

Doctoral students who have an upcoming dissertation oral defense are posted here. So why not take this opportunity to learn about the research that our graduate students are doing!

Dissertation Defense for Monica Schwehr


Department Contact Email: earth.sciences@unh.edu


Defense Date and Time: 10/15/15 12:40 pm

Defense Location: James 254

Defense Advisor: Margaret Boettcher

Defense Abstract: Mid-ocean ridge transform faults (RTFs) are typically viewed as geometrically simple, with fault lengths readily constrained by the ridge-transform intersections. This relative simplicity, combined with well-constrained slip rates, make them an ideal environment for studying strike-slip earthquake behavior. As the resolution of available bathymetric data over oceanic transform faults continues to improve, however, it is being revealed that the geometry and structure of these faults can be complex. To better determine the resolution of structural complexity on RTFs, as well as the prevalence of RTF segmentation, fault structure is delineated on a global scale. Segmentation breaks the fault system up into a series of subparallel fault strands separated by a an extensional basin, intra-transform spreading center, or fault step. Earthquakes on RTFs are known to be small, to scale with the area above the 600C isotherm, and to exhibit some of the most predictable behaviors in seismology. In order to determine whether this segmentation affects the global RTF scaling relations, the scalings are recomputed using an updated seismic catalog and fault database in which RTF systems are broken up according to their degree of segmentation. Finite element analysis is used to model 3-D RTF fault geometry assuming a viscoplastic rheology in order to determine how segmentation affects the thermal area above the 600C isotherm. In the models, fault segment length, length and location along fault of the intra-transform spreading center, and slip rate are varied in order to model a wide range of possibilities. A new scaling relation is developed for the critical fault offset length (OC) that significantly reduces the thermal area of adjacent fault segments, such that adjacent segments are fully decoupled at 4OC. The relationship between fault structure and seismic behavior is directly addressed on the Discovery transform fault, located at 4S on the East Pacific Rise. One year of microseismicity recorded on an OBS array, and 24 years of Mw >=5.4 earthquakes obtained from the Global Centroid Moment Tensor catalog, are correlated with surface fault structure delineated from high-resolution multibeam bathymetry. Each of the 15 Mw >= 5.4 earthquakes was relocated into one of five distinct repeating rupture patches, while microseismicity was found to be reduced within these patches.


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