Controls on rift localization in the melt-poor Malawi (Nyasa) Rift from high-resolution seismic imaging of the crust

Northern Arizona University, Flagstaff AZ

Investigators

Abstract

Continental rifts are places where continents break apart, leading to earthquakes and volcanic eruptions and eventually, the formation of new ocean basins. The East Africa Rift System (EARS) is among the few locations on Earth where continental rifting is going on right now and can be observed. Gaherty, Shillington, and their research team will analyze seismic data collected as part of a previous NSF project to create high-resolution images of the the rifting crust in Malawi and Tanzania. These images should shed light on how rifts form and grow - specifically, whether EARS rifting in the Lake Malawi region is happening at a boundary between different types of crust or where bodies of magma have weakened the crust. The seismic images will also allow scientists to precisely locate earthquakes, which is required to understand earthquake risk and identify possibly dangerous hidden faults. Geraghty, Shillington, and their team will coordinate with geological survey departments in both Malawi and Tanzania to share their scientific results and improve understanding of earthquake risk in both countries. This project will also provide training for three early-career scientists at Northern Arizona University: an undergraduate research assistant, a PhD student, and a post-doctoral researcher. The project will develop three-dimensional (3D) models of crustal seismic wavespeeds (Vp and Vs) in the Malawi rift through joint analysis of co-located active- and passive-source seismic data collected in and around northern Lake Malawi in 2013-2015 as a part of the SEGMeNT project. Recordings of airgun shots from SEGMeNT’s marine geophysical survey in Lake Malawi at both lake-bottom and on-shore seismometers provides the basis for a regional-scale 3D P-wave tomography of the entire crust, including Moho geometry. High-frequency ambient noise Rayleigh waves recorded across the onshore-offshore broadband array provide high-resolution constraints of 3D Vs structure within the crust. These constraints will be integrated in a joint inverse-modeling analysis, producing a comprehensive set of self-consistent Vp, Vs, and Vp/Vs models of the crust that should allow the researchers to quantify: (1) the presence and spatial variability in depth-dependent stretching within and around the Malawi Rift axis; (2) the location of transitions between ancient crustal terranes, and their correspondence to regions of rift localization; and (3) the possible presence of unerupted magmatic products within and/or at the base of the crust, and its possible relationship to ancient terrane sutures. Taken together, these inferences will significantly improve the understanding of the dominant weakening processes underlying the Malawi Rift and other magma-poor rifts worldwide. Partners at the Geological Surveys in both Malawi and Tanzania will directly contribute to the modeling effort, facilitating transfer of the improved understanding to reducing geohazard in the region. The project provides education and training support for three early-career scientists at Northern Arizona University, including an undergraduate research assistant, a PhD student, and a Post-Doctoral Scientist. 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.