Journal Article

Double Reservoirs Imaged Below Great Sitkin Volcano, Alaska, Explain the Migration of Volcanic Seismicity

Roman, Diana C., Haney, Matthew, Yang, Xiaotao, Kupres, Cody A.

2023

Overview

Volcanic seismicity provides essential insights into the behavior of an active volcano across multiple time scales. However, to understand how magma moves as the eruption cycle develops, better knowledge of the geometry and physical properties of the magma plumbing system is required. In this study, using full‐wave ambient noise tomography, we image the three‐dimensional (3‐D) crustal shear‐wave velocity structure below Great Sitkin Volcano in the central Aleutian Arc. The velocity model reveals two low‐velocity anomalies correlating with the migration of volcanic seismicity. With a bulk melt fraction of about 2.5%–9%, these low‐velocity anomalies are interpreted as mushy magma reservoirs. We propose a six‐stage eruption cycle to explain the migration of seismicity and the alternating eruption of the two reservoirs with different recharging histories. These findings have broad implications for the dynamics of magma plumbing systems and the structural control of eruption behaviors. Plain Language Summary Understanding magma accumulation and transport systems below active volcanoes is essential for predicting eruption behavior and assessing the potential hazards. The distribution of earthquakes can partly be used to infer the development of magmatic activity at different times. However, to understand how magma moves at different stages of an eruption cycle, better knowledge of what the magma plumbing system looks like is necessary. In this study, we use an advanced seismic imaging method to construct the 3‐D crustal shear‐wave velocity structure below Great Sitkin Volcano in the central Aleutian Arc. The velocity model reveals two crustal magma reservoirs, which correlate with the migration of seismicity. We propose a six‐stage eruption cycle to explain the evolution of seismicity in space and time across the island and the alternating eruption of two reservoirs. The findings in this study help to understand better the control of eruption behaviors by the underlying magma plumbing system at active volcanoes. Key Points The pre‐ and co‐eruptive seismicity below Great Sitkin Volcano, Alaska, shows a spatiotemporal migration A new 3‐D shear‐wave velocity model reveals two crustal low‐velocity anomalies that correlate with the migrating seismicity We propose a six‐stage eruption cycle involving two magma reservoirs to explain the long‐term and short‐term seismicity patterns

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Ambient noise / Anomalies / Behavior / Earthquakes / Eruptions / Great Sitkin / Hazard assessment / Lava / Magma / Magma chambers / magma reservoir / migration of volcanic seismicity / Physical properties / Plumbing / Reservoirs / seismic imaging / Seismic velocities / Seismicity / Shear / Tomography / Transportation systems / Velocity / Volcanic activity / volcanic eruption cycle / Volcanic eruptions / volcanic seismicity / Volcanoes / Wave velocity