EARTHQUAKES IN THE CONTINENTAL CRUST
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Continental earthquakes are one of the most widely observable indicators of on-going continental lithospheric deformation. Accurate earthquake depth estimates are critical to tectonic interpretations, yet depths are not reliably provided by global earthquake catalogs and bulletins. Therefore, separate analyses are needed to determined accurate earthquake depths. In this thesis, I compile accurate estimates of continental earthquake depths and combine them with complementary datasets, such as topography, subsurface structural interpretations, and lithospheric thickness estimates, to investigate continental deformation. I present results of focal mechanisms and accurate depth estimates for continental earthquakes throughout the Central Andes of South America. Through integration with high resolution topographic data and interpretations of subsurface structures, I find the following: (1) earthquakes in the foreland and Eastern Cordillera are consistently associated with basement-involved deformation, (2) earthquake focal mechanism P axis orientations indicate an east-west crustal shortening direction in the forelands, (3) local orientations of deformational structures influence earthquake focal mechanism orientation, and (4) normal and strike-slip focal mechanisms beneath southern Peru and northernmost Chile are consistent with the effects of the increase in vertical compressive stress, due to high topography and thick crustal root of the plateau, superimposed on the stress orientations seen in the foreland. I also conduct a global study of the depth distributions of continental earthquakes by synthesizing previously reported accurate earthquake depth determinations to investigate in what tectonic settings lower crustal earthquakes occur in an attempt to understand their significance to lithospheric strength and deformation. I find that deep continental crustal earthquakes occur within stable lithosphere and within tectonically active lithosphere at a transitional state of lithospheric thickness and crustal deformation.
earthquakes; continental crust
Dissertation or Thesis