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Persistent Seismicity and Missing Eruptivity: Analysis and Classification of 2003-2019 Earthquakes Recorded at Gareloi Volcano, Aleutian Islands, Alaska

Session: Waveform Cross-Correlation-Based Methods in Observational Seismology [Poster]

Type: Poster

Date: 4/21/2021

Presentation Time: 03:45 PM Pacific

Description: 

Mount Gareloi, one of the westernmost volcanoes in the Aleutian arc, has not erupted since 1989, yet it displays extremely high levels of volcanic seismicity on a daily basis. Hundreds of earthquakes are recorded per day on the island since seismometer installation in 2003. We analyzed and classified seismic data collected from 2003-2019 to explore the geophysical processes causing the consistent seismicity with no subsequent eruptive activity. Analysis of waveforms and their corresponding spectra indicate the vast majority of Gareloi earthquakes are characterized by frequencies between 1 and 4 Hz, which are typical of long period (LP) events. Approximately 5,900 earthquake hypocenters calculated by the Alaska Volcano Observatory (AVO) were relocated using the algorithm hypoDD. From 2003-2007, hypocenters locate shallowly between 2 and 10 kilometers depth, while seismicity from 2016-2019 was broadly deeper, between 6 and 16 kilometers depth and included significantly more high frequency (HF) events. Although relocated hypocenters have similar spatial distribution to the initial locations, events from 2003-2007 cluster more tightly and vertically beneath the island, whereas events from 2016-2019 are more scattered through the region with no obvious clustering. Unfortunately, the seismic network experienced numerous station failures from 2008-2015, resulting in inconsistencies within the AVO catalog. Thus, we cannot accurately determine when the transition to deeper, more scattered hypocenters and the increase in HF events occurred. Cross correlation of waveforms provides evidence of repeating LP earthquakes directly associated with Gareloi from May through July of 2007 and few repeating earthquakes from 2008-2019. Based on these analyses, we attribute the shallow LP events of 2003-2007 to volcanic processes while the shift to deeper hypocentral depths coincides with the increase in HF activity and may reflect a change in the magmatic system at Gareloi.

Presenting Author: Kiana T. Harris

Student Presenter: Yes

Authors