Circulation-Informed Seafloor Geodetic Techniques for Understanding Plate Boundary Processes

Abstract

Tectonic plate boundaries host a range of solid-Earth physical processes of scientific and societal interest, including the majority of the world’s volcanism and earthquakes. However, these marginal systems are primarily found offshore beneath the Earth’s oceans, posing significant challenge for effective observation and study. One such process is the generation of shallow slow slip events (SSEs), which in recent years have been identified in a number of subduction zones globally using observations of seafloor pressure. Such records are also sensitive to oceanographic circulation processes, which can obscure potential SSE signals and lead to false detections. In this dissertation, I present methods for understanding and eliminating oceanographic pressure signals so that tectonic signals may be more readily identified and characterized. In Chapter 2, I use data from the 2011-2015 Cascadia Initiative Experiment to show that the oceanographic noise on tidally filtered, detrended seafloor pressure records can be reduced from >6 cm to <1 cm root-mean-square (RMS) by correcting with a reference pressure record from a comparable depth and further show that such corrections enable the detection of a range of Mw ~6 synthetic SSE scenarios. In Chapter 3, I use data from the 2018-2019 Alaska Amphibious Community Seismic Experiment to compare a variety of oceanographic pressure proxies and demonstrate that correcting seafloor pressure records with the first Complex Empirical Orthogonal Function (CEOF) and differencing with a depth-matched pressure record yield the greatest signal RMS reduction and enable the detection of >2 cm SSE signals on the continental slope and >4 cm SSE signals on the continental shelf. In Chapter 4, I calculate seafloor pressure from a regional oceanographic model of the Cascadia region and show that mesoscale eddies traveling over the continental margin can generate SSE-like signals in pressure records, which may lead to false detections. Finally, in Chapter 5, I present seafloor and on-land observations from a novel tiltmeter design that provides a means of recording and correcting instrumental drift, with parallels to comparable drift issues in standard pressure sensors.