Velocity Changes Associated With the Three Year Buildup of Activity at Great Sitkin Volcano, Alaska – Are Precursory Signals Detectable?

Date: 4/26/2019

Time: 06:00 PM

Room: Fifth Avenue

Great Sitkin volcano is located in the western Aleutian Islands, Alaska near the town of Adak where large explosive eruptions have the potential to impact local and trans-Pacific air traffic and produce ashfall on populated areas. In the spring of 2016, earthquake activity at Great Sitkin began a steady increase over background levels. The heightened activity further increased in the summer of 2018 but has leveled off in early 2019. In January 2017, the first of 9 explosions occurred with 6 of the 9 explosions recorded between Aug-Nov 2018. While the explosions are thought to be phreatic in origin, an explosion in June 2018 is known to have deposited ash, although the ash is thought to be fragmented country rock rather than juvenile material. Identifying potential precursors before explosions could help improve eruption forecasts if the current increase in seismicity continues.

Previous studies have proposed that seismic velocity changes, dv/v, may precede volcanic eruptions via ascent of magmatic material and volatile fluids. Such changes are useful for forecasting possible eruptions. It has been shown that these changes in aquifer depth and pore fluid pressurization have the potential to decrease seismic velocity on the order of 0.1%. In this work, we look for velocity changes over the long buildup of activity at Great Sitkin. To do this, we cross-correlate synchronous seismic data from pairs of stations and calculate dv/v from a moving reference. We also examine the auto-correlations of stations. Of particular interest in our analysis is whether velocity changes are different prior to the June 2018 event compared to the other explosions.

Presenting Author: Paul Bremner

Authors