Constraining cycles of deformation at submarine plate boundaries using cabled ocean bottom seismometers

Abstract

The processes that reorganize the Earth’s crust occur primarily beneath our oceans, where it is difficult to make observations. Much of our knowledge of deformation at mid-ocean ridges and subduction zones is therefore limited to large events that can be recorded on land, including dike emplacements and moderate to large earthquakes. Although these large deformation events are thought to relieve most of the strain built up by plate motions, some fault slip can occur in the interim. Close seafloor observation of seismic signals at mid-ocean ridges and subduction zones between large events is needed to properly constrain how fault slip varies across frictional conditions and to address hazards associated with offshore faults. In this dissertation, I leverage novel cabled ocean bottom seismometer (OBS) datasets, which provide the first long-term (> 10 year) time series of seafloor seismic activity, to constrain deformational behavior between large events at submarine plate boundaries. In Chapter 2, I combine cabled OBS data from the Endeavour segment of the Juan de Fuca ridge with past autonomous OBS datasets to create an earthquake catalog that tracks how activity evolves between dike emplacements in relation to regional tectonics, magmatism, and hydrothermal fluid circulation. In Chapter 3, I show how just one cabled OBS can be used to constrain earthquake rates at the Endeavour segment, which allows the earthquake catalog to be extended by five years and supports that seismicity rates remain relatively low for most of the spreading cycle. In Chapter 4, I investigate multiplet earthquakes, groups of earthquakes with highly similar waveforms, at the Endeavour segment. I show that they represent a range of fault slip types, including fluid-induced earthquake swarms and repeating earthquakes, which provide the first direct evidence for aseismic slip at a mid-ocean ridge. Finally, in Chapter 5, I develop a new approach to search for tectonic tremor, a signal associated with slow fault slip, on individual OBSs. Application of this approach to cabled seismometers in the Cascadia subduction zone finds potential tectonic tremor signals that suggest localized shallow slow slip may occur near the deformation front.