Seismic Velocity Changes Associated With the 2018 Collapse of Kīlauea’s Summit

Date: 4/26/2019

Time: 08:45 AM

Room: Puget Sound

Several weeks after the eruption of lava began in the lower east rift zone of Kīlauea volcano in 2018, seismicity at the summit settled into a remarkably cyclic pattern: increase in number and size of earthquakes, culminate in a ~M5 collapse event, quiescence, then increase and repeat again. Deformation at the summit was also similarly cyclic. Overprinted on a general trend of deflation as magma exited the shallow reservoir, steps of inflation occurred at the times of the large collapse events. Using a repeating earthquake catalog, we solved for changes in seismic velocity in the shallow subsurface with half-hourly temporal resolution using coda wave interferometry. To first order, seismic velocity changes as a function of volumetric strain, where velocity decreases as cracks open in dilatation. We also solved for temporal changes in mean free path related to crack formation with a similar technique.

We find that over the duration of a single cycle, velocity decreased prior to the collapse event and immediately increased afterwards. These changes likely reflect the opening and closing of cracks due to volumetric strain caused by elastic rebound from slip on the newly formed caldera walls and/or changes in pressure in the shallow magmatic system. Over the course of the last two months of the eruption, long-term trends in the seismic velocity timeseries can be divided into two linear segments: a decrease in velocity of ~5% from early to late June, and then roughly constant velocities in July through the end of the eruption in early August. We interpret the long-term velocity decrease was related to crack formation and opening during the creation of the ring fault outlining the roof block above the shallow magmatic system. Then, the constant velocities were due to a stable configuration of the system where the episodic sliding and down-dropping of the roof along that established margin did not further open cracks.

Presenting Author: Alicia J. Hotovec-Ellis

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