Seismic Attenuation and Earthquake Stress Drop in the Tonga and Pampean Flat-Slab Subduction Zones.

다국어 초록 (Multilingual Abstract)

Subduction zones play a crucial role in plate tectonics, governing lithospheric material recycling, the generation of arc magmatism, and causing seismic hazards. However, within subduction systems, key properties of earthquakes and mantle wedge structures remain difficult to constrain because seismic observations recorded at the Earth's surface contain mixed contributions from earthquake source processes, wave propagation through the Earth, and receiver effects. In particular, seismic attenuation, which measures energy dissipation during wave propagation and is sensitive to temperature and partial melt, remains less well constrained than seismic velocity. This dissertation investigates earthquake source parameters and seismic attenuation structure in two subduction zone endmembers: the fast and hot Tonga subduction zone in the South Pacific, as well as the cold and hydrated Pampean flat slab region in the south-central Andes.Chapter 1 provides an overview of the thesis. Chapter 2 develops a transdimensional 3D body wave attenuation tomography methodology and applies it in the Tonga subduction zone, enabling characterization of model uncertainty and providing constraints on complex melting mechanisms in back-arc spreading centers. Chapter 3 examines earthquake source properties in the Pampean flat-slab region, focusing on stress drop estimates, their spatial variability, and correlations with fluid-related processes in both the overriding crust and within the subducting slab. Chapter 4 presents 3D body wave attenuation models for the Pampean region, using the improved methodology and independent source constraints, providing constraints on mantle heterogeneities and the complex fault systems within the overriding lithosphere.Overall, these results demonstrate that attenuation models, derived using the improved methodology with independently constrained source parameters, significantly enhance our understanding of subduction environments. By studying the two endmember subduction systems, this work provides a plausible methodological framework for broader attenuation studies, provides new observations of attenuation and stress drop in the Tonga and Pampean regions, and insights into the role of fluids and slab geometry in controlling subduction zone processes.