Migrating tremors indicate the activation of distributed melt bodies days before the 2015 Axial Seamount eruption

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Abstract
The traditional view that volcanoes are underlain by a single, melt-dominated magma chamber has recently evolved into the idea that subsurface melt is heterogeneously distributed in a larger magma domain. While seismic imaging of small melt bodies beneath subaerial volcanoes remains difficult, melt bodies located several kilometers from mid-ocean ridge axes and submarine volcanic edifices have been identified. Nevertheless, the connectivity of these melt bodies within the magma domain and their role during eruptions remain unclear. We analyzed continuous ocean-bottom seismic data recorded in 2015–2025 CE that detected 415 volcanic tremor episodes that emerged ~60 h before, and continued during, the 2015 Axial Seamount eruption. The volcanic tremors initiated ~19 km southeast of the caldera before migrating into it and showed spatial overlap with funnel-shaped axial melt lenses and/or lithosphere-asthenosphere boundaries. Our results suggest that these volcanic tremors reflect the activation of or transport through distributed melt bodies over 10 km from the caldera, which provided enhanced magma supply for Axial Seamount's eruption and highlight a broader interconnected active magma plumbing system where melt can be mobilized within a matter of days for an eruption.

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