Spatiotemporal Seismic Structure Variations Associated With the 2018 Kīlauea Eruption Based on Temporary Dense Geophone Arrays

During the 2018 Kīlauea volcanic eruption, lava erupted from a series of new fissures in the lower East Rift Zone more than 30 km away from the summit through a dike intrusion. Between late May and early August, variations in the effusion rate at the persistent eruptive vent (Fissure 8) were observed following near‐daily summit caldera collapse events. Targeting the ongoing eruptive activity and the subsurface magma movement, we deployed a temporary dense seismic array. The observed time‐lapse changes in seismic velocity associated with the response of the summit collapse in three areas are presented in this study. The results show (1) clear spatially dependent co‐collapse velocity reductions across the newly‐intruded dike structure, (2) a gradual post‐collapse velocity increase near Fissure 8 correlated with the surge of magma supply, and (3) a gradual post‐collapse velocity increase on the summit likely associated with reservoir pressurization and crustal welding. Plain Language Summary Volcanic eruptions commonly involve failure of rocks surrounding the subsurface magma transport system, such as fracturing and rupturing. During the 2018 Kīlauea volcano eruption, lava mainly erupted from new fissures within the lower East Rift Zone (LERZ) located tens of kilometers away from the magma reservoir beneath the summit. As magma drained from the summit system to feed the LERZ eruption, the summit caldera subsided in an episodic fashion through a series of 62 collapses. Despite this spatial separation, we observe correlation between the summit collapse and the LERZ eruptive activity suggesting the two features are interconnected through a subsurface dike. To better study the eruption dynamics and subsurface magma movement, we deployed a temporary dense seismic array across the Kīlauea volcano system during the steady phase after mid‐June in 2018. In this study, we present the time‐lapse changes in crustal seismic velocity observed across the dense array correlated with the summit collapses. We show that different volcanic components (i.e., summit, dike, and fissure) react to summit magma pressurization differently. Our findings provide new constraints on the time‐evolving mechanical structure of a volcano during a major eruption. Key Points Temporary seismic array targeting ongoing eruptive activity permits studies on dynamics between preexisting and newly formed structures We observe spatially dependent seismic velocity variations associated with the newly int