Joint ESC/VSC Seminar: Damage and Stress-Induced Seismic Velocity Changes During the Progressive Collapse of Kīlauea’s Summit
Alicia Hotovec-Ellis, USGS Volcano Science Center
Wednesday, August 28, 2019 at 10:30 AM
- Building 3, Rambo Auditorium
The detection of small, spatiotemporal changes in seismic velocity structure has shown promise in recent years as a tool for monitoring volcanoes. Much of this promise is due to the repeated observation that seismic velocity decreases prior to volcanic eruptions. These decreases are thought to occur in response to the opening and closing of cracks and are considered a proxy for volumetric strain. However, it is unclear which specific underlying processes create velocity changes. Kīlauea Volcano, Hawai‘i, and its dense, modern geophysical monitoring network, is an ideal natural laboratory to test hypotheses about the genesis of seismic velocity changes. Using coda-wave interferometry of repeating earthquakes during the last two months of the summit eruption in 2018, we measured velocity changes with sub-hourly temporal resolution and compare these results with other timeseries of seismicity and deformation.
The Kīlauea summit caldera collapsed in a series of events with near-daily periodicity spanning mid-May through early August. Seismic velocity also showed a pattern of near-daily cyclicity in phase with seismicity levels and deformation, where velocity increased at the time of each collapse and slowly decreased between them. Multiple processes provide possible explanations for this cycle, including pressurization of the shallow magmatic system and stress-induced dilatation. Long-term trends in the seismic velocity timeseries can be divided into two distinct periods: a linear decrease in velocity from early to late June, followed by overall constant velocity in July through the end of the eruption in early August. We propose the first phase to be related to crack development and opening during the formation of the ring fault outlining the roof block above the shallow magmatic system, and the second phase to the down-dropping of the roof along that established margin.