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World map of Holocene volcanoes with reported observations of deep long-period (DLP) earthquakes in the literature. Included are volcanoes with observed DLPs (red triangles), volcanoes where the seismic data were reviewed for DLPs at some point, but none was found (blue triangles), and volcanoes without reported DLPs (open circles). A table of volcanoes with documented DLPs is included in the S.I. The inset shows Alaska-Aleutian volcanoes that are the focus of this study. The different symbols indicate whether volcanoes have four or more seismometers (triangles) or fewer than four (circles). Blue-filled symbols have bubble-corrected melt inclusion (MI) data. Yellow-filled symbols have the required combination of Nb trace element data, whole-rock geochemistry, volatile, and isotope data for Method A (Chem.), and green-filled symbols have both (MI + Chem.). The base maps are crustal thickness (Mooney et al. 2023).
DLPs and Volatiles
DLPs and Volatiles
Understanding magma and volatile behavior and movement through the upper mantle and crust is critical to connecting subduction processes with shallow melt accumulation in the run-up to many volcanic eruptions. However, this depth zone is difficult to probe. Deep long-period earthquakes (DLPs, 0.5 to 5 Hz peak frequencies) are observed beneath volcanoes in this depth zone, 10 to 50+ km BSL. As such, DLPs may provide insight into the deep magmatic plumbing system and transport processes of magma and fluids, yet their source process remains elusive. Models suggest that DLPs may result from magma movement, volatile exsolution, or thermal stresses from cooling magma. I am leading a combined geophysical and geochemical investigation into DLPs along the Alaska-Aleutian arc. We compare the multi-decade Alaska Volcano Observatory seismic catalog with geochemical and geophysical constraints on magma storage and the initial depth of volatile exsolution. We observe higher rates of DLPs at 30-35 km BSL, which align with vapor-saturated melts at the top of the mantle. Then, we observe increasing DLPs from 27 to 10 km depth, which parallels the depths of melt inclusion entrapment and the modeled volatile proportion (McKee et al., 2026).
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