Relationship between seismic swarms and episodic inflations at Akutan Volcano in Alaska

Seismic swarms at volcanic regions are important manifestations of volcanic unrest. While they are often inferred to be related to fluid or magma movements, their underlying process remains an active research topic. In particular, quantifying the proportion of seismic swarms that are related to magma movement can potentially improve their utility for eruption forecasting. To better understand the relationship between seismic swarms and magma movement, we focus on the Akutan volcano where episodic inflations have been recorded every 2-3 years since 2002. We first applied template matching on continuous seismic waveforms between 2005-2017 to improve the earthquake catalog’s magnitude of completeness. We further classified the events as long-period (LP) or regular volcano-tectonic (VT) events based on their frequency content. After waveform-based double-difference relocation, we find that the VT and LP events are concentrated above and below the shallow magma reservoir respectively. We clustered the VT and LP events based on their spatiotemporal evolution and find that most clusters are swarm-like with no clear mainshock-aftershock sequences. Based on their temporal relation to the inflation episodes, we infer that the LP swarms are related to ascending magma into the shallow reservoir, which sometimes triggers VT swarms through stress transfer.