Global Seismic Imaging of the Oceanic Plates

The outer layer of the earth is composed of rigid tectonic plates, like a cracked eggshell. These plates slide around the surface of the planet over a weaker, hotter layer below. The transition from rigid plate to the mantle below is fundamental to plate tectonics and our existence on the planet. However, the definition of the plate, i.e., their thickness, defining mechanism, and degree of coupling to the layer below are not well-known.

I will use global seismic imaging to understand the thickness and defining mechanism of the Earth's oceanic plates. The ocean plates cover 70% of Earth's surface, yet are rarely mapped at high resolution given the remoteness, and the difficulty and cost of deploying seismometers to the bottom of a 4 km deep ocean. I have developed a new methodology to map the plates in locations where station coverage is sparse, as it is beneath the oceans. I use the SS waveform, which is an S wave that has bounced once at Earth's surface. Subtle variations in the character of the SS wave give information on the depth and character of the base of the tectonic plate in the region of the bouncepoint.

I will use a newly compiled global database (1990 - 2011) which is nearly 4TB in size, and represents about four-times the data in my previous investigations. The significance is that I will be have nearly perfect resolution across all ocean basins, enabling global comparisons and a unified view of the tectonic plate.

The definition of the plate has implications for many processes that impact human existence. It has a fundamental control on how plates move. This includes the generation of earthquakes, volcanoes, and tsunamis. Therefore a better understanding will lead to better hazard assessment and mitigation of natural disasters. In addition, plate thickness and strength directly affects uplift and subsidence of the tectonic plate. These forces impact mountain building and sea level rise, and are therefore important factors in understanding climate change.

The results from this study will change text books, and clarify fundamental questions. I will develop a better understanding of the definition of a tectonic plate, including its formation and evolution. Understanding the ocean plates is fundamental to any tectonic setting in that they likely play a large role in the formation of the continents. Overall, this work will deepen our understanding of plate tectonics.

This research will have three major classes of beneficiaries:

(1) The solid earth scientific community (geologists, petrologists, and geophysicists) will benefit from this large-scale investigation of a fundamental boundary both scientifically and from method and code development and the availability of models, codes, and data for future work.

(2) The public will benefit through outreach activities, and also better assessment and mitigation of natural disasters and constraints on climate change. Educators will benefit from a clearer understanding of a fundamental boundary that is traditionally skipped glossed over in textbooks.

(3) Climate change scientists & hazard assessment scientists though tighter constraints on the forces causing seafloor subsidence and general lithosphere-asthenosphere interactions.

We will interact with these beneficiaries by:

(1) Running special sessions at conferences (AGU/EGU) to highlight new results and integrate various scientific fields. Not only links in sold-earth geophysics, but also climate and hazard assessment will be discussed.

(2) Outreach to the UK community in ongoing programs at University of Southampton

(3) Websites for the public, educators, and researchers including downloadable codes.

(4) Data sharing.

Measures of success will include:

Level of access to the websites

Number of downloads of the analysis codes

Number of submissions to the special conference session

Uptake of the methods by other academics

Number of attendees at Ocean and Earth Day

Number of schools visited by KE officer and other linked staff

Number of requests for the database

Number of citations from outside the seismology field