Both volcano-tectonic (VTs) and deep long-period earthquakes (DLPs) have been documented at Akutan Volcano, Alaska and may reflect different active processes. In this study, we perform high-resolution earthquake detection, classification, and relocation using seismic data from 2005-2017 to investigate their relationship with underlying magmatic processes. We find that the 2,787 VTs and 787 DLPs are concentrated above and below the shallow magma reservoir respectively. The DLPs' low-frequency content is likely a source instead of path effect considering its uniformity across stations. Both VT and DLP swarms occur preferentially during inflation episodes with no clear migration. However, the largest VT swarms occur during non-inflating periods, and only VT swarms contain repeating events. Therefore, we conclude that the VTs represent fault rupture triggered by magma/fluid movement or larger earthquakes, while the DLPs are directly related to unsteady magma movement through a complex pathway or represent slow fault ruptures triggered by magma movement.

<p>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.</p>

Seismometers are the most commonly deployed monitoring sensors on volcanoes (Saccorotti & Lokmer, 2021) as exemplified by the seismic networks maintained by the Hawaiian (Nakata & Okubo, 2010) and Alaska (Power et al., 2013) volcano observatories. Over the years, development in volcano seismology has given rise to several successes in eruption forecasting. Precursory increases in seismicity rate are detected sometimes before major eruptions (R. A.