INTEGRATING GEOPHYSICAL METHODS TO STUDY SUBDUCTION ZONE PROPERTIES, ACTIVE FAULTING IN A VOLCANIC FIELD, AND VOLCANO LANDSLIDE HAZARDS

In this dissertation, I integrate geophysical data to study the upper crustal structure of subduction zones and its influence on earthquake, volcanic, and landslide hazards from the trench to the volcanic arc. Specifically, I use seismic reflection data, earthquake focal mechanisms, magnetics, and electromagnetics to study three actively deforming regions: 1) the Cascadia subduction zone deformation front in the Pacific NW of the United States, 2) the near surface of the Laguna del Maule volcanic field in the southern Andes of Chile, and 3) the edifice of Iliamna Volcano in the US state of Alaska. Active seismic and acoustic methods provide high resolution (down to cm-scale) studies of the upper crust (meters to tens of km), enabling analysis of physical properties and interpretation of deformation history. By processing and interpreting marine multichannel seismic reflection data offshore Washington state, I illuminate the location, structure, and sediment velocity of an anomalously quiet plate boundary, utilizing the long offset data to improve estimates of sediment velocity. The resulting velocity model indicates that there is a high velocity basal sedimentary unit on the megathrust plate boundary. I interpret that this unit is mechanically strong and may have higher strain accumulation potential, offering clues as to why Cascadia produces rare but large earthquakes. At the rapidly inflating Laguna del Maule volcanic field, I combine high resolution lacustrine acoustic reflection data, lacustrine magnetics, and local earthquake focal mechanisms to locate and characterize hidden, active faults that I interpret to facilitate magmatic inflation. I measure differences in sediment thickness across these faults to identify pre-historic inflation and deflation events, and use deposition rates to estimate timing of these events. These cycles of localized inflation temporally correlate with a spatially migrating magmatic center over the past 23,000 years. At Iliamna Volcano, a site of recurrent landslides and active fumaroles with difficult ground access, airborne geophysics enables subsurface mapping of weak rocks on the edifice. I combine magnetic and electromagnetic data to model the thickness and location of fluid saturated and geochemically altered rocks beneath the steep-sloped, ice-covered edifice and use the extent of the altered material to model slope stability. The resulting slope stability models indicate an edifice that is almost entirely unstable under wet conditions with the potential to produce collapse scars >400 m thick which are likely to flow towards the coast, leading to potential tsunami hazards.

Name thesis:degree_name

Ph. D., Geological Sciences

Level thesis:degree_level

Doctor of Philosophy

Discipline thesis:degree_discipline

Geological Sciences

Grantor

Cornell University

Year dc:date.issued

2020

Author dc:creator

• Peterson, Dana

Committee members dc:contributor.committeemember

• O'Rourke, Thomas Denis
• Abers, Geoffrey

• Alaska
• Cascadia
• Chile
• seismology
• tectonics
• volcanoes

Statement dc:rights

• Attribution 4.0 International

Licence dc:rights.uri

• https://creativecommons.org/licenses/by/4.0/

Language dc:language.iso

en

DOI

https://doi.org/10.7298/r8h5-5h63

Dc Identifier Other

ProQuest Submission ID: 12297
ProQuest Publication ID: 28150202

OAI identifier oai:identifier

oai:ecommons.cornell.edu:1813/103356