Date of Award

2025

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Geophysics (PhD)

Administrative Home Department

Department of Geological and Mining Engineering and Sciences

Advisor 1

Roohollah Askari

Committee Member 1

Gregory P. Waite

Committee Member 2

Snehamoy Chatterjee

Committee Member 3

Vijaya V.N. Sriram Malladi

Committee Member 4

Seiji Nakagawa

Abstract

Long-period (LP) seismic events, commonly recorded in volcanic and hydrothermal environments, are widely attributed to the resonance of fluid-filled fractures and the excitation of Krauklis waves along the solid-fluid interface. These low-velocity, dispersive waves are sensitive to both fluid dynamics and fracture geometry, offering critical insights into subsurface fluid transport, fracture evolution, and seismic source processes. Despite robust theoretical treatments, experimental validation under realistic geological conditions has remained limited. To address this, I aimed to develop a series of laboratory-based experimental models that systematically investigate the key physical mechanisms driving LP signal generation. In the first set of experiments, I have examined how steady-state fluid flow within a tri-layer aluminum crack model affects Krauklis wave propagation. Our results reveal that flow direction and rate affect the wave velocity, amplitude, resonance frequency, and quality factor, highlighting the role of dynamic fluid conditions in shaping LP characteristics. Building on this, we constructed a large-scale concrete slab embedded with a customized crack model to study the influence of fluid viscosity, crack stiffness, and triggering location on resonance behavior. These experiments confirm theoretical predictions and help isolate parameter-specific effects on LP generation. Finally, we expanded the investigation to consider the role of fracture orientation by comparing horizontally and vertically aligned cracks using waveform analysis and Moment Tensor inversion. This revealed orientation-dependent frequency content and spatial distribution of resonance modes, providing a nuanced view of source geometry effects. Together, these three studies constitute a unified experimental and modeling framework that bridges the gap between theory and observation in LP seismology. By isolating the influence of fluid xvii flow, fracture properties, and source orientation, our work provides new benchmarks for interpreting LP events in complex geological settings such as active volcanoes, geothermal systems, and hydraulically fractured reservoirs.

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