Caribbean Subduction: Seismic Imaging of Melt and Volatiles in the Lesser Antilles with joint inversion, full-waveform, and machine learning approaches

Project Rationale
Dense oceanic tectonic plates sink beneath buoyant continental plates at subduction zones. The ocean plate adds volatiles like water to the mantle, lowering the melting temperature, and enabling melting and eventually creating volcanoes at Earth’s surface. Subduction zones are an important part of plate tectonics, in particular regarding the input of volatiles like water to the system. The pathways of volatiles and melting in subduction zones are relatively unknown, and yet fundamental to our understanding of the forces that drive melting and dictate the location of volcanoes. This study will image fluids, volatiles and melt in the Lesser and Greater Antilles Subduction Zone using data from a new 34 instrument seismic deployment on the ocean floor and also stations located on Caribbean Islands. This is the first time Atlantic Plate subduction has been imaged at this scale and resolution. It represents an exciting opportunity to investigate an ocean plate formed at slow spreading, the role of fracture zones and detachment faulting in the downgoing plate on water storage and transport, and a large, systematic variation in ocean plate sedimentation within one system.

Methodology
Seismic methods such joint seismic inversions, including combinations of body waves, surface waves, and/or receiver functions will be employed. The project also has the possibility of full waveform modelling using finite difference or SPECFEM approaches and/or developing joint interpretation and/or inversion with magnetotelluric data collected on Antigua . These images will provide powerful constraints since shear velocity is strongly affected by volatile content and the ratio of shear velocity to compressional velocity is strongly affected by melt. The joint inversions will represent the culmination of the project and will be fully integrated with geochemistry and geodynamic modelling. The goal will be a systematic global evaluation of volatiles and melting in subduction systems. The project also has the potential to evolve to broader implications for subduction zones and fluid pathways globally. Machine learning could be utilized to further investigate interdisciplinary aspects of the results, such as the physical and chemical implications for a range of geophysical and geochemical constraints. The results could also be placed into a global context through inversions using the global seismic database, also via machine learning approaches.

Training
All doctoral candidates will enroll in the Graduate School of NOCS (GSNOCS), where they will receive specialist training in oral and written presentation skills, have the opportunity to participate in teaching activities, and have access to a full range of research and generic training opportunities. GSNOCS attracts students from all over the world and from all science and engineering backgrounds. There are currently around 200 full- and part-time PhD students enrolled (~60% UK and 40% EU & overseas). Specific training will include:

The student will gain experience with cutting edge ocean bottom seismic equipment.
The student will develop skills and learn techniques from passive source seismology as a member of one of the largest and most active geophysics groups in the UK. The student will learn to cull, process, and invert seismic data using dense seismic arrays. The student will have excellent computational facilities and be trained in programming skills for Python, Seiscomp3, FORTRAN, Matlab, SAC, and the UNIX operating system. The student will integrate the seismic results with petrologic and active seismic experiments currently being done in the region by collaborators at Univ. Bristol, University of Durham and Imperial College London to collaborate with colleagues. A wide range of opportunities to develop the range of generic skills essential for successful completion of the PhD and their future career are available through the Graduate School NOCS including geophysical fieldwork. This training will prepare the student for a career path in academia and industry.