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Field imaging spectroscopy and inferring a blind thrust earthquake history from secondary faulting : 1944 San Juan Earthquake, Argentina

  • Author(s): Ragona, Daniel Eduardo
  • et al.
Abstract

The studies presented in this dissertation provide new approaches to extract paleo-earthquake information from the geological record. The first chapter describes the development of Field Imaging Spectroscopy, a new methodology for data acquisition and analysis in paleoseismology. The study shows the steps followed from data acquisition, pre-processing, processing and analysis of high spatial and spectral resolution images obtained from cores and a large sample from a fault zone collected at Hog Lake, San Jacinto Fault, Southern California. The study demonstrate that hyperspectral data can be obtained in the field using portable scanners and that high spatial and spectral resolution in the visible to short wave infrared provide a way to enhance subtle or invisible stratigraphic and structural features. The second chapter focuses on the use of neural networks and naïve Bayesian classifiers to automatically classify hyperspectral image data, providing an objective mapping of the structure of cores, samples and field exposures. The results of this study show that a system integrated by a hyperspectral scanner and pattern recognition algorithms can work as an enhanced eye and an objective classifier to provide the geologist with additional information that facilitates the final description, interpretation and correlation of the geology in paleoseismic exposures and cores. The hyperspectral dataset collected together with a spectral library of the materials observed in the excavation provide a new way to archive paleoseismological data for future analysis. Finally, in chapter 3, an innovative approach to study blind thrust faults is presented. The study of the secondary La Laja fault near San Juan, Argentina shows that the earthquake history recorded in a minor fault provides an indirect way to study the occurrence of large M̃7 earthquakes at depth. This investigation also provides the first and perhaps the longest record of the earthquake activity of a blind thrust fault in the world, as well as the most detailed and complete study of past earthquakes in the Argentinean Andes. It also set a good precedent for similar studies in other structures in other regions of the world where the earthquake hazard related to blind thrust faults is largely un-assessed

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