Seamounts, or submarine volcanos, have two distinct phases: the formation phase when the seamount is magmatically active and the passive phase when the seamount is transporting on the seafloor until subduction. Being able to understand various aspects of seamounts both in the formation and passive phase can enhance our understanding of volcanic processes and how seamounts can influence other processes such as crustal deformation, plate subduction, and earthquake generation. The purpose of this thesis is to examine seamounts on the Juan de Fuca plate both in the formation and passive phases.
The first three chapters of this thesis focuses on understanding the subsurface properties and volcanic processes of Axial Seamount, an active seamount located on the Juan de Fuca Ridge. The fourth and final chapter focuses on understanding how seamounts influence subduction and the seismogenic properties of the Cascadia Subduction Zone. In chapter 1, I analyze multichannel seismic data to characterize the internal crustal structure of the rift zones of Axial Seamount. The new reflectivity images reveal small and discontinuous crustal magma bodies beneath and in the vicinity of the rift zone lava flows from the three most recent eruptions. We also image wide magma bodies within the overlap regions between the rift zones and neighboring segments of Juan de Fuca Ridge. Collectively the new observations indicate that multiple small crustal magma bodies underlie Axial and likely contribute to rift zone magmatism with implications for interpretations of seismicity patterns and lava flow compositions.
In chapters 2 and 3, I process over 7 years of continuous seismic noise at Axial Seamount and use cross-correlation functions to calculate the relative seismic velocity (dv/v) changes beneath the caldera. I find a long-term trend of decreasing velocity during rapid inflation, followed by slight increase in velocities as background seismicity increases and inflation rate decreases. I also observe small short-term increases in dv/v which coincide with short-term deflation events. The observations of changes in dv/v and their correlation with other geophysical data provide insights into how the top ~1 km of the crust at Axial Seamount changes in response to subsurface magma movement and capture the transition from a period of rapid reinflation to a period where the caldera wall faults become critically stressed and must rupture to accommodate further inflation. From the relative seismic velocity variations, I also observe a strong annual pattern constrained within the 0.1-0.2Hz filter band. This annual pattern correlates well with timing and location of storm activity within the Pacific Ocean. Through the comparison of annual variation with ocean data, we determine that the annual pattern observed is likely an apparent velocity change due to changes in the seismic noise source.
Lastly, in chapter 4, I utilize multichannel seismic data and high-resolution P-wave velocity (Vp) models of the CASIE21 expedition to calculate residual Vp models to examine properties of the sediments relative to seamounts on the incoming plate. At one of the larger seamounts located within 25km of the deformation front, I show evidence consistent with predicted stress effects of buried topography where there is an increase in normal stresses landward and a stress shadow seaward of the seamount, which can alter and impact rupture patterns along the margin. I also show evidence for signatures of enhanced hydrothermal
circulation at seamounts near the deformation front which show that seamounts can be potential carriers of additional fluid into the margin when subducted. In additional to looking at the sediments relative to the seamounts, I also evaluate properties of a high Vp basal layer that is prevalent on all of the lines which can provide insights into the earthquake rupture and tsunami potential for the area.
| Identifer | oai:union.ndltd.org:columbia.edu/oai:academiccommons.columbia.edu:10.7916/ytyg-ee71 |
| Date | January 2024 |
| Creators | Lee, Michelle Khuu |
| Source Sets | Columbia University |
| Language | English |
| Detected Language | English |
| Type | Theses |
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