ABSTRACT
Continental rifting is a fundamental process of plate tectonics that has been shaping our planet for billions of years. The northern East African Rift system, including the Gulf of Aden and the Red Sea, presents an excellent opportunity to study this process in locations sub-aerially prior to continental break-up, through to full seafloor spreading. We present results from anisotropic surface wave imaging of the region’s crust and uppermost mantle. Anisotropic structures provide additional information about the form of structures at depth and deformation in the region. We find low seismic velocities within the Main Ethiopian Rift (MER), the Red Sea and Gulf of Aden that likely represent melt emplaced in the crust and uppermost mantle. Radial anisotropy, defined as a difference in wave speed of vertically versus horizontally polarized seismic waves, is observed across the region but is strongest within the rift. The strength of radial anisotropy in the MER suggests that horizontally layered melt intrusions are the dominant mode of melt storage in the mid to lower crust. Azimuthal anisotropy, defined as a variation in seismic wave speed as a function of direction, shows complex patterns that are likely related to ancient structures away from the rift, and structures related to extension and melt emplacement within the rift. Taken together, our results suggest melt has played an important role in shaping the crustal structure within the rift and may have also shaped the ancient pre-rift crustal structure.
