Recording Earthquakes in the Oceans for Global Seismic Tomography by Freely-Drifting Robots

Abstract

This dissertation describes the treatment of data recorded by a novel instrument named MERMAID, short for Mobile Earthquake Recording in Marine Areas by Independent Divers. MERMAID is a passively-drifting float that autonomously records and transmits seismograms of teleseismic earthquakes from the global oceans. The primary goal of the instrument is to fill a seismic data gap. The primary goal of this dissertation is to describe how MERMAID data are analyzed and interpreted to achieve this end. We begin by developing a new method to pick multiscale arrival times of seismic phases in its noisy seismograms and further to assign uncertainty estimates and confidence intervals to those times. Our method is first applied to data collected in the Indian Ocean and the Mediterranean Sea. It is able to able to identify multiple phases that traveled different routes through the Earth with high accuracy and low uncertainty. Next we describe an ongoing deployment of 50 MERMAIDs in the South Pacific. There we study the seismicity rates yet reported and project for the total volume of data we expect returned over the lifetime of the deployment. We again use our method of arrival-time and uncertainty estimation to add to our ever-growing catalog of MERMAID travel-time residuals, and compute a similar catalog using seismograms from traditional seismometers installed on islands proximal to our floats. Their agreement proves that MERMAID records tomographically-useful data. We use these residuals to provide the first analyses of travel-time anomalies for the new ray paths sampling the mantle under the South Pacific. Finally, we end with a description of the open-source software developed over the course of this research and note that it may be used to reproduce the results of this dissertation.