High-Resolution Crustal Velocity Response to the 2018 Kīlauea Eruption Using Temporary Dense Geophone Arrays

Abstract:

Between May and August 2018, the Kīlauea eruption was predominantly focused on a persistent eruptive vent, Fissure 8, in the Lower East Rift Zone (LERZ). The magma was supplied from the summit reservoir, more than 30 km away, through an underground dike structure. Following near-daily summit caldera collapse events, a surge of magma influx driven by reservoir pressurization migrated down to the LERZ and caused an increase in effusion rate observed at Fissure 8. Targeting the ongoing eruptive activity and the subsurface magma movement, we deployed a dense nodal geophone array across the Kīlauea volcano system from mid-June through mid-July 2018. Using seismic noise coda wave interferometry, we investigate the time-lapse changes in seismic velocity associated with the crustal response to the summit collapse and the resultant dynamic magma pressurization between the summit and the LERZ. Across the LERZ dike, we observe a clear co-collapse velocity reduction followed by an exponential recovery. A maximum velocity drop of ~0.27% is observed immediately above the presumed dike structure indicating that the medium in the immediate vicinity of the dike is more susceptible to dynamic weakening. Adjacent to Fissure 8, we observe a gradual velocity increase of ~0.18% with a maximum amplitude ~2–3 hours after the collapse. We interpret this as the surge of magma influx within the dike in response to summit reservoir pressurization, which requires a compliant and elastic-walled dike structure. At the summit, we observe a gradual velocity increase of ~0.34% with a maximum amplitude that peaks ~4 hours after the collapse. We interpret the observed variation as the superposition of two distinct exponential relaxation processes in response to the instantaneous pressurization from the reservoir and the following depressurization from the progressive magma removal. In addition to the crustal velocity structure, we will be exploring advanced seismic event identification and characterization incorporating data from the dense array within the LERZ. This area is relatively seismically quiet based on the current seismic catalog. However, based on preliminary results, there seems to be higher seismicity rates in the LERZ during the eruption in the enhanced catalog, which can provide for a better understanding of eruption dynamics.