Improving deformation modeling at Axial Seamount using bathymetry and realistic magma reservoir geometry

Axial Seamount is one of the best-studied submarine volcanoes with a vertical deformation time series documenting the last three eruptions in 1998, 2011, and 2015. Improved geodetic modeling of Axial, especially in the context of the existing time series covering a wide spectrum of volcanic activity, will aid in understanding how magma transport and storage are related to surface deformation, seismicity, and eruption timing. Here we use finite element models to explore the effect of bathymetry and realistic main magma reservoir (MMR) geometry on predicted ground deformation due to MMR recharge. The MMR geometry is defined by directly implementing the three-dimensional top and bottom MMR horizons imaged using tomography by Arnulf et al. (2018). The models reproduce uplift following the 2015 eruption through 2020, constrained using vertical displacements from 9 seafloor benchmarks where pressure measurements are made within the caldera (Nooner & Chadwick, 2016; Hefner et al., 2021) and from repeated autonomous underwater vehicle (AUV) bathymetric surveys extending outside the caldera (Caress et al., 2020). We compare modeled deformation results to previously proposed source models (prolate spheroid, Nooner & Chadwick, 2016; sphere and rectangular sill, Hefner et al., 2021). Results using the realistic MMR geometry are in progress, but including seafloor bathymetry decreases the root mean squared error between the deformation data and the modeled displacements by 48.4%, increases the volume change estimate by 28%, and increases the maximum surface deformation by 14.3%.