Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - EURO-LAB (Experiment to Unearth the Rheological Oceanic Lithosphere-Asthenosphere Boundary)

Teaser

Plate tectonics has been a fundamental tenet of Earth Science for nearly 50 years, butfundamental questions remain, such as where is the base of the plate and what makes a plate,“plate-like?” A better understanding of the transition from the rigid lithospheric plate to the...

Summary

Plate tectonics has been a fundamental tenet of Earth Science for nearly 50 years, but
fundamental questions remain, such as where is the base of the plate and what makes a plate,
“plate-like?” A better understanding of the transition from the rigid lithospheric plate to the weaker
mantle beneath – the rheological lithosphere-asthenosphere boundary (LAB) - has important
implications for the driving forces of plate tectonics, natural hazard mitigation, mantle dynamics,
the evolution of the planet, and climate change. There are many proxies used to estimate the
depth and nature of the base of tectonic plates, but to date no consensus has been reached. For
example, temperature is known to have a strong effect on the mechanical behaviour of rocks.
However, it has also been suggested that the chemical composition of the plate provides additional
strength or that melt weakens the mantle beneath the plate.

This project is designed to systematically image an oceanic plate beneath the Atlantic
from birth at ridge to 40 My old seafloor. We deploy ocean bottom seismometers (OBS) and
magnetotelluric (MT) instruments, and to image the plate at a range of resolution scales
(laterally and in depth) and sensitivities to physical and chemical properties. This large, focused,
interdisciplinary effort will finally determine the processes and properties that make a plate strong
and define it. The results will be put in context through seismic imaging in other locations and also through global seismic imaging.

Work performed

We organised the use of seismic instruments from the US and France via contracts.

We deployed and recovered the seismic and MT instruments at the mid-Atlantic ridge.

We performed data quality tests and also a series of corrections to the data. We made timing corrections, solved for instrument orientation, and corrected for tilt and compliance.

We solved for sediment characteristics using P-to-S conversion from the base of the sediment. (Agius et al., 2018)

We processed gravity, swath, and magnetics. (Harmon et al., 2018)

We have our first results from S-to-P imaging, surface wave tomography, body wave tomography, local seismicity, SKS splitting, and MT - all in prep.

Final results

We have been able to do much more than image the tectonic plate beneath the mid-Atlantic. We also developed a method to characterise sediment. We are have investigated ruptures of large nearby earthquakes. We have imaged the tectonic plate beneath Cascadia (Rychert et al., 2018) and also continents globally (Tharimena et al., 2017).