Abstract
Observing changes in the magmatic system of an active volcano before and during an eruption is imperative to the forecasting of volcanic eruptions, which are among the most destructive geological phenomena on Earth, causing significant environmental and societal hazards. Cross-correlation of seismic ambient noise has become a popular tool to detect variations in the subsurface velocity structure and numerous studies have investigated pre-eruptive changes at active volcanoes. In this study, we examine temporal velocity variations associated with the 2020-2021 eruption of Kilauea volcano in Hawai'i, the first major eruptive activity at Kilauea since the marked 2018 eruption. We downloaded hourly continuous waveform data from the Incorporated Research Institutions for Seismology (IRIS) from 60 days before to 30 days after the onset of the eruption on December 20, 2020. We focus on the data recorded by the eight broadband seismic stations around the summit caldera and in the Middle East Rift Zone operated by the U.S. Geological Survey Hawaiian Volcano Observatory. After the removals of trend, mean, and instrument response, the data were resampled to a uniform 100-Hz sample rate and bandpass filtered from 1 to 5 Hz. Cross-correlation functions of the hourly segments were calculated for 28 station pairs and then stacked for each day during the study period. A time-domain stretching method was applied to these stacked cross-correlation pairs and a best-fitting set of velocity changes was solved for the entire study period. We observe a velocity decrease in the days leading to the eruption, which may be related to magma/fluid/gas movement or an increase in pressure in the crust. We find that cross-correlation of ambient noise continues to show promise in revealing precursors of volcanic eruptions. Our study may provide insight into how a volcano adjusts after a large expulsion of material and collapse.