Abstract
On 27 September 2014, Ontake volcano, in central Japan, suddenly erupted without precursory activity. We estimated and tracked the source locations of volcanic tremor associated with the eruption at high temporal resolution, using a method based on the spatial distribution of tremor amplitudes. Although the tremor source locations were not well constrained in depth, their epicenters were well located beneath the erupted crater and the summit. Tremor sources were seen to descend approximately 2 km over a period of several minutes prior to the beginning of the eruption. Detailed analysis of the time series of tremor amplitudes suggests that this descent is a robust feature. Our finding may be an important constraint for modeling the 2014 eruption of Ontake volcano as well as for monitoring activities on this and other volcanoes.
Highlights
Ontake volcano, in central Japan, is the nation’s second highest volcano with an elevation of 3067 m
Source locations of volcanic earthquakes As a check of the amplitude source location (ASL) method, we compared locations of volcano tectonic earthquakes at Ontake estimated by the ASL with the locations estimated from phase arrivals of P and S waves by Tokyo VOIC
To estimate an error of the ASL method, we added random fluctuations to the site amplification factor of each station based on the assumption that the site amplification factor follows a log-normal distribution, we conducted a grid search 100 times for each event with the fluctuated site amplification factors
Summary
In central Japan, is the nation’s second highest volcano with an elevation of 3067 m. On-site survey estimated that the eruption occurred between 13 and 18 May. Preceding the eruption, seismicity at Ontake had increased since late April and many tremors were observed at the same time (Matsumoto Weather Station 1991; Nagoya University 1991).
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