Relative Source Locations of Continuous Tremor Before and After the Subplinian Events at Shinmoe‐dake, in 2011

Abstract

Volcano monitoring systems are not always ready to resolve signals at the onset of eruptive activity. This study makes use of stations installed later to calibrate the performance of the stations that had been operated before the eruption. Seven stations recorded continuous volcanic tremor before and during the subplinian eruptions of Shinmoe-dake, Japan, in 2011. We estimated the source locations of the tremor using the amplitude distribution. The stability of the analysis was obtained by careful selection of time windows in which signals from a single source are dominated. The site effects and the regional attenuation factor were evaluated using tremor recorded after the major eruptions by a dense seismic array and a good number of stations. A tremor source changed its depth beneath the crater for 1 week before the major eruption, rising from a depth of a few kilometer to the water layer 3 times, each of which occurred following shallow inflation and minor eruptions. It is interpreted as migration of gas probably with magma, which further transported heat to the water layer and triggered the subplinian eruptions. Plain Language Summary Shinmoe-dake, Japan had a relatively large eruption in 2011 for the first time in 300 years. Although continuous seismic signal, which is called tremor, indicating magma or gas movement had been recorded before the main eruptive event, we did not have sufficient seismic stations to capture the magma movement. After the main eruption, more seismic stations were installed and recorded tremor that continued with less energetic eruptions. In this study, we make use of the data after the main eruption to calibrate the performance of the stations that had been operated before the eruption. We successfully revealed the movement of the tremor source before the eruption in correlation with shallow inflation and precursory eruptions. The result was interpreted as movement of magma and gas that supplied heat to the water layer in the ground and triggered the eruption. It is demonstrated that seismic stations even deployed after an eruption are useful in assessing processes preceding the eruption.

Locating hydrothermal fluid injection of the 2018 phreatic eruption at Kusatsu-Shirane volcano with volcanic tremor amplitude

“…However, amplitude variations of observed coda-wave affect the estimation of , and it causes potential errors for source location estimates (Ogiso et al, 2016;Walsh et al, 2017). Following Ichihara and Matsumoto (2017), the present study determines setting a reference time window that the source location is fixed at a certain point. In our case, a reference window is set from 10:02:10 with source location at the surface of the center of main vents ( Fig.…”

“…However, since no seismic station covers the south of Motoshirane, gridsearch for the minimum residual needs to be modified to suit our network configuration. Hence, we follow an improved version of the ASL proposed by Ichihara and Matsumoto (2017) for searching the minimum residual and determination.…”

“…Previous studies have demonstrated that seismic analysis is vital for understanding the phreatic eruption mechanism and related hydrothermal activities with locations, force system, and its temporal changes of seismic wave sources (e.g., Jolly et al, 2010;Kato et al, 2015;Maeda et al, 2015;Yukutake et al, 2017;Jolly et al, 2018). Amplitude Source Location (ASL) method has been applied at a lot of volcanoes to constrain the source location of volcanic tremor (e.g., Yamasato, 1997;Aki, 2003, Kumagai et al, 2010;Kurokawa et al, 2016;Ichihara and Matsumoto, 2017;Ichimura et al, 2018;Walsh et al, 2019). Since no investigation has been reported at Motoshirane in terms of geophysical ground observations, our primal objective is to locate where the hydrothermal fluid that drove the 2018 phreatic eruption came from.…”

Estimation of Relative Source Locations From Seismic Amplitude: Application to Earthquakes and Tremors at Meakandake Volcano, Eastern Hokkaido, Japan

“…Because the ASL method does not rely on phase arrival times, it is applicable to seismic events with unclear onset times, such as tremors. The ASL method has been applied to tremors and earthquakes within volcanoes (Battaglia 2003;Ogiso and Yomogida 2012;Kumagai et al 2013a;Kurokawa et al 2016;Ichihara and Matsumoto 2017;Walsh et al 2017;Ichimura et al 2018;Kumagai et al 2019), pyroclastic flows (Yamasato 1997;Jolly et al 2002), lahars or debris flows (Kumagai et al 2009;Ogiso and Yomogida 2015;Doi and Maeda 2020), and snow avalanches (Pérez-Guillén et al 2019). The ASL method has also revealed the source process of a large subduction zone earthquake (Kumagai et al 2013b), the detailed distribution of shallow low-frequency earthquakes near a trench axis (Tamaribuchi et al 2019).…”

Amplitude Source Location Method With Depth‐Dependent Scattering and Attenuation Structures: Application at Nevado del Ruiz Volcano, Colombia

“…The amplitude source location (ASL) method proposed by Yamasato () and Battaglia and Aki () and the seismic amplitude ratio method of Taisne et al () have enabled the locations of LP and VLP events and tremor with emergent onsets to be determined. These methods use high‐frequency seismic amplitudes and assume isotropic radiation of S waves and have been widely applied to volcanoseismic signals at various volcanoes (Battaglia, ; Battaglia, Aki, & Ferrazzini, ; Battaglia, Aki, & Staudacher, ; Caudron et al, ; Caudron, Taisne, et al, ; Caudron, White, et al, ; Ichihara & Matsumoto, ; Ichimura et al, ; Jolly et al, ; Kumagai et al, ; Kumagai et al, ; Kumagai, Palacios, et al, ; Kumagai et al, ; Kumagai et al, ; Kumagai et al, ; Kurokawa et al, ; Maeda et al, ; Ogiso et al, ; Ogiso & Yomogida, , ; Tan et al, ; Walsh et al, ; Walter et al, ). These methods have also been used to detect moving sources of tremor signals associated with eruptions (Ichihara & Matsumoto, ; Kumagai, Palacios, et al, ; Ogiso & Yomogida, ), magmatic intrusions (Caudron et al, 2018b; Taisne et al, ), and lahars (Ogiso & Yomogida, ).…”