Monitoring changes in seismic velocity related to an ongoing rapid inflation event at Okmok volcano, Alaska

Abstract

Okmok is one of the most active volcanoes in the Aleutian Arc. In an effort to improve our ability to detect precursory activity leading to eruption at Okmok, we monitor a recent, and possibly ongoing, GPS‐inferred rapid inflation event at the volcano using ambient noise interferometry (ANI). Applying this method, we identify changes in seismic velocity outside of Okmok's caldera, which are related to the hydrologic cycle. Within the caldera, we observe decreases in seismic velocity that are associated with the GPS‐inferred rapid inflation event. We also determine temporal changes in waveform decorrelation and show a continual increase in decorrelation rate over the time associated with the rapid inflation event. The magnitude of relative velocity decreases and decorrelation rate increases are comparable to previous studies at Piton de la Fournaise that associate such changes with increased production of volatiles and/or magmatic intrusion within the magma reservoir and associated opening of fractures and/or fissures. Notably, the largest decrease in relative velocity occurs along the intrastation path passing nearest to the center of the caldera. This observation, along with equal amplitude relative velocity decreases revealed via analysis of intracaldera autocorrelations, suggests that the inflation source may be located approximately within the center of the caldera and represent recharge of shallow magma storage in this location. Importantly, there is a relative absence of seismicity associated with this and previous rapid inflation events at Okmok. Thus, these ANI results are the first seismic evidence of such rapid inflation at the volcano.

Temporal Changes of Seismic Velocity Caused by Volcanic Activity at Mt. Etna Revealed by the Autocorrelation of Ambient Seismic Noise

“…Our results give an exclusive insight into the dynamics and the development of explosive and effusive eruptions, specifically when looking at the remarkable link between seismic velocity variation and ground deformation. Several existing studies have associated variations of seismic velocity and cycles of inflation and deflation with changes in magma pressurization (e.g., Brenguier et al, 2008;Bennington et al, 2015;Hotovec-Ellis et al, 2015;Donaldson et al, 2017). The compression associated with an increase in magma pressurization is expected to close pores and cracks in the medium, causing an increase of the elastic moduli and the seismic velocity, along with a potential inflation at the surface (O'Connell and Budiansky, 1974).…”

Decrease in Seismic Velocity Observed Prior to the 2018 Eruption of Kīlauea Volcano With Ambient Seismic Noise Interferometry

“…Ambient noise studies do not require an active source or repeating earthquakes and have been successfully applied to measure changes in seismic velocity in a range of different environments, such as volcanoes Donaldson et al, 2017;Sánchez-Pastor et al, 2018;Sens-Schönfelder & Wegler, 2006), landslides (Mainsant et al, 2012), underground mines , geothermal reservoirs (Hillers et al, 2015;Obermann et al, 2015), active faults zones , earthen dams (Olivier et al, 2017;Planès et al, 2015), and other environments. Notably, it has been shown that a detectable change in seismic velocity occurs in the days leading up to an eruption at some volcanoes (Bennington et al, 2015;Budi-Santoso & Lesage, 2016;Caudron et al, 2015;Grêt et al, 2005;Hirose et al, 2017;Patanè et al, 2006;Ratdomopurbo & Poupinet, 1995;Wegler et al, 2006). These virtual source signals can be constructed at different times, so small temporal changes in seismic velocity can be measured to study processes in the Earth's crust.…”

“…These virtual source signals can be constructed at different times, so small temporal changes in seismic velocity can be measured to study processes in the Earth's crust. Notably, it has been shown that a detectable change in seismic velocity occurs in the days leading up to an eruption at some volcanoes (Bennington et al, 2015;Budi-Santoso & Lesage, 2016;Caudron et al, 2015;Grêt et al, 2005;Hirose et al, 2017;Patanè et al, 2006;Ratdomopurbo & Poupinet, 1995;Wegler et al, 2006). Authors in these studies attribute precursory velocity changes to the dilation/compression of the edifice due to the increased pressure the magma chamber exerts on the edifice, which has been shown to cause measurable changes in seismic velocities at volcanoes (Sens-Schönfelder et al, 2014).…”

Inferring Magma Dynamics at Veniaminof Volcano Via Application of Ambient Noise

“…For the set of NCFs associated with the 2004 and 2013 eruptions at Veniaminof, narrow frequency band ANI analyses yielded wildly varying changes in seismic velocity with large associated error bars. Thus, we cannot apply the same methodology as Lesage et al (2014) and Bennington et al (2015). We present an alternative approach to estimate the frequency at which changes in seismic velocity occur in the time leading to eruption.…”

“…First, we utilize the technique of ambient noise interferometry (ANI), which detects subtle changes in seismic velocity associated with changes in the material properties of the subsurface. ANI has become a well‐established technique for identifying magmatic activity at active volcanoes (e.g., Bennington et al, ; Brenguier et al, ; Budi‐Santoso & Lesage, ; Duputel et al, ; Haney et al, ; Mordret et al, ; Obermann et al, ). This method typically uses ambient noise data derived from pairs of seismic stations; however, Haney et al () and De Plaen et al () demonstrate that changes in seismic velocity can also be determined using ambient noise data determined from individual stations.…”