ABSTRACT

New seafloor is continuously formed at the center of Earth?s deep oceans, where the tectonic plates spread apart and cause hot magma to rise to the surface. Where the plates move apart more slowly, as happens over vast tracts of the Atlantic, Indian and Arctic oceans, deep-seated rocks from Earth?s mantle are exhumed, dragged up by slip on enormous, long-lived, faults called detachments and without significant eruption of lava. Creation of new oceanic seafloor by slip on these recently discovered faults is poorly understood, yet may play a fundamental role in paving a large part of our planet?s surface. One of the best ways to understand the behavior of these faults is to study the seismic waves caused by the small earthquakes that are triggered as the faults slip. This project examines earthquake data from a segment of the Mid-Atlantic Ridge near 13°N, where detachment faults are prevalent. The data were recorded by instruments placed on the seabed in 2016 by scientists from the UK, as part of a wider coordinated international effort to understand oceanic detachment faulting. This project fosters international collaboration between the USA, UK and France, and supports an early-career researcher.

Observations of oceanic detachment faulting to date have mostly been limited to seabed sampling and mapping, leaving many questions about the structure and processes taking place beneath the seafloor unanswered. One of the most critical outstanding questions today is whether or not along-axis adjacent oceanic detachments are connected by a continuous fault in the sub-surface. An effective way to tackle this question is by studying naturally occurring seismicity generated as deformation takes place in the detachment fault system, which allows for direct imaging of fault structures and surfaces. While several local seismicity surveys have now been conducted at oceanic detachments, none of them has deployed a seismic network with sufficient aperture to constrain the along-axis extent of individual detachments. This project uses data from a 58 ocean bottom seismometer (OBS) deployment on the Mid-Atlantic Ridge at 13°N that extends ~30 km along the ridge axis and provides dense spatial coverage over two active detachment faults and the intervening ridge axis. This network, deployed by UK scientists to record airgun shots from an active-source seismic experiment, contains tens of thousands of local microearthquakes that will help determine whether or not the two core complexes at 13°20'N and 13°30'N are connected by a single fault surface.

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