Descent of tremor source locations before the 2014 phreatic eruption of Ontake volcano, Japan

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.

Special issue “The phreatic eruption of Mt. Ontake volcano in 2014”

“…Ontake, rapid growth of tremor activity (Fig. 3 of Ogiso et al 2015) and tilting (Fig. 7 of Takagi and Onizawa 2016) were observed about 7 min before the eruption.…”

“…Maeda et al (2015) infer crack opening immediately before the eruption. Ogiso et al (2015) track the source location of tremor beneath the crater. Finally, Terakawa et al (2016) reveal stress changes associated with the eruption, strongly implying fluid-pressure changes.…”

“…They infer that hydrothermal fluid flowed through the crack toward the surface. Ogiso et al (2015) use the spatial amplitude distribution of tremor data associated with the eruption to track the source location of the tremor. They find that it was located beneath the crater and descended 2 km over the course of several minutes following the onset of the eruption; this appears to be a robust solution.…”

Mineralogical study on volcanic ash of the eruption on September 27, 2014 at Ontake volcano, central Japan: correlation with porphyry copper systems

“…Miyagi et al (2014) reported that the volcanic ash consists exclusively of hydrothermally altered minerals with minor primary igneous particles. Some geophysical studies have reported analyses on seismicity linked to the eruption, investigating pre-and post-eruptive processes (e.g., Kato et al 2015;Maeda et al 2015;Ogiso et al 2015).…”

Groundwater pressure changes and crustal deformation before and after the 2007 and 2014 eruptions of Mt. Ontake

“…The toll of dead and missing was 63 (e.g., Cyranoski 2014). The seismic activities including tremors linked to the 2014 eruption have been deeply analyzed Maeda et al 2015;Ogiso et al 2015).…”