Subdivision of Seismicity Beneath the Summit Region of Kilauea Volcano: Implications for the Preparation Process of the 2018 Eruption

Long-period (LP), hybrid, and volcano-tectonic (VT) seismicity are important indicators for tracking the evolution of volcanic processes. Here, we propose an unsupervised learning method to classify 5,949 seismic events in Kilauea volcano, Hawai'i, during a 4-month period before the collapse of Pu'u' O'o on April 30, 2018. The LPs and hybrids exhibit three major episodes, which progressively intensified and had increasing shallow events toward the eruption. The most intense episode starting 3 weeks before eruption coincides with changes in near-caldera deformation and lava lake elevation in Halema'uma'u, serving as possible immediate precursors. However, the first two episodes imply magma migration was already active months prior to the eruption. The spatiotemporal patterns of abundant hybrids reveal that they are associated with magma movement but mixed with shear-failure or near-surface resonance. Our results provide useful constraints on the magmatic processes in the preparation phase of the Kilauea eruption in 2018. Plain Language Summary Many volcanoes around the world have been known to produce different types of seismic events, which can be used to infer volcanic processes underneath. However, classification of these events remains a challenging task. We propose a new classification method and apply it to numerous seismic events in Kilauea volcano, Hawai'i, before the collapse of Pu'u' O'o in 2018. We successfully separate different types of events and observe interesting spatiotemporal patterns. The results show that, before the eruption, the long-period and hybrid events have three episodes. Together with surface observations, the latest episode in April 9-27 shows an unusually high rate and more shallow origins, indicative of the impending eruption. In addition, the spatiotemporal patterns of hybrid events shed light on their physical mechanisms. These results provide useful constraints on the magma migration processes in the preparation phase of the Kilauea eruption in 2018. Key Points We classify long-period, volcano-tectonic, and hybrid events by spectral dissimilarity and hierarchical clustering The unusual high seismicity rate and more shallow origins in the last episode in April 9-27 may be indicative of the impending eruption The spatiotemporal patterns of hybrid events shed light on their physical mechanisms