Collaborative Research: Chain Transform Fault: Understanding the dynamic behavior of a slow-slipping oceanic transform system

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A longstanding goal of Earth Science is to understand why some sections of faults slip in large earthquakes while other sections do not. Oceanic transform faults are ideal for studying fault slip due to their simple composition and predictable motion - yet the spectrum of behavior on these faults is poorly understood. This study will employ a range of techniques to study the Chain transform fault in the equatorial Atlantic, which is an ideal locality due to its variable seismicity and its bathymetric expression that is typical of many transform faults. This project will train early career scientists in interdisciplinary marine science through their participation in research cruises and their analyses of data and samples. A broader cross-section of students will be engaged through a multi-institution virtual course on marine geology and geophysics. Oceanic transform faults consist of sections that slip in large earthquakes separated by sections that are primarily aseismic. Oceanic transform faults also display a variety of structural features – valleys, transverse ridges, median ridges, flower structures, fault segmentation – whose origins are linked to stress, strain, and material properties. A two-cruise experiment will be used to probe these fault dynamics. The first cruise aboard the R/V Langseth will collect multi-channel seismic data and deploy 20 ocean bottom seismometers. A year later, a second cruise will recover seismometers, deploy the autonomous underwater vehicle Sentry for high-resolution geophysical surveys, and use dredging to sample the active fault zone. These datasets will connect surface observations of fault structure and composition to seismic constraints at depth. Goals include:• Substantially advancing current understanding of slow-slipping transform faults.• Surface-to-depth images of fault structures from seismic data and Sentry micro-bathymetry.• Identification of active fault strands and areas of active uplift based on linking microseismicity patterns and focal mechanisms to fault structures.• Deciphering how strain is accommodated on poorly coupled portions of the fault, and whether, and at which depth, those portions are characterized by swarms of microseismicity, as has been observed at faster slipping transform faults.• Determination of the dominant lithologies in the fault zone—including in uplifted structures—using samples, photo transects, and seismic velocity.• Elucidation of the role of fluids in modifying fault-slip behavior, based on sample analyses, chemical-sensor datasets, seismic-velocity variations, and microseismicity distribution.• Location of sites of magmatic activity within a slow spreading transform and evaluation of source variability, melting systematics, and storage depths from magma compositions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.