Volcano Seismicity in Alaska

Abstract

I examine the many facets of volcano seismicity in Alaska: from the short-lived

eruption seismicity that is limited to only the few weeks during which a volcano is active,

to the seismicity that occurs in the months following an eruption, and finally to the longterm

volcano seismicity that occurs in the years in which volcanoes are dormant.

I use the rich seismic dataset that was recorded during the 2009 eruption of

Redoubt Volcano to examine eruptive volcano seismicity. I show that the progression of

magma through the conduit system at Redoubt could be readily tracked by the seismicity.

Many of my interpretations benefited greatly from the numerous other datasets collected

during the eruption. Rarely was there volcanic activity that did not manifest itself in some

way seismically, however, resulting in a remarkably complete chronology within the

seismic record of the 2009 eruption. I also use the Redoubt seismic dataset to study post-eruptive seismicity. During

the year following the eruption there were a number of unexplained bursts of shallow

seismicity that did not culminate in eruptive activity despite closely mirroring seismic

signals that had preceded explosions less than a year prior. I show that these episodes of

shallow seismicity were in fact related to volcanic processes much deeper in the volcanic

edifice by demonstrating that earthquakes that were related to magmatic activity during

the eruption were also present during the renewed shallow unrest. These results show that

magmatic processes can continue for many months after eruptions end, suggesting that

volcanoes can stay active for much longer than previously thought.

In the final chapter I characterize volcanic earthquakes on a much broader scale

by analyzing a decade of continuous seismic data across 46 volcanoes in the Aleutian arc

to search for regional-scale trends in volcano seismicity. I find that volcanic earthquakes

below 20 km depth are much more common in the central region of the arc than they are

in the eastern and western regions. I tie these observations to trends in magma

geochemistry and regional tectonic features, and present two hypotheses to explain what

could control volcanism in the Aleutian arc.