Detection of crustal deformation prior to the 2014 Mt. Ontake eruption by the stacking method

Abstract

The phreatic eruption of Mt. Ontake in central Japan occurred in September 27, 2014. No obvious crustal deformation was observed prior to the eruption, and the magnitudes of other precursor phenomena were very small. In this study, we used the stacking method to detect crustal deformation prior to the eruption. The stacking method is a technique to improve the signal-to-noise ratio by stacking multiple records of crustal deformation. We succeeded in detecting a slight crustal deformation caused by a volume change in the shallow region beneath the volcano's summit from 1 month prior to the eruption. We also detected a slight crustal deformation that may have been caused by a volume increase in the deep region from one and a half months before the eruption. The magnitude of the volume change in the shallow region did not differ significantly in the 2014 eruption compared to the volume change during the small Mt. Ontake eruption in 2007, and the volume change in the deep region was rather smaller in 2014 than in 2007.

Migration of seismic activity associated with phreatic eruption at Merapi volcano, Indonesia

“…According to their interpretation, decompression caused by the transition of the volcanic fluid to a gaseous phase would propagate simultaneously downwards in the hydrothermal systems and upward, opening cracks beneath the crater. Ascending sources have been identified by other analyses, migration of seismicity (Kato et al, 2015) and ground inflation detected by tiltmeter (Miyaoka and Takagi, 2016). At Merapi, we observe both directions of migration, but shifted in time.…”

Heat source of the 2014 phreatic eruption of Mount Ontake, Japan

“…GNSS data indicate that the ground inflated by 0.38 × 10 6 m 3 7 min prior to the eruption, although the volume change at depth was comparatively small (Takagi and Onizawa, 2016). Stacking of GNSS data revealed that a small volume change occurred immediately beneath the summit from 1 month prior to the eruption, as well as a small volume increase at depth from 1.5 months before the eruption (Miyaoka and Takagi, 2016). These volume increases were much smaller than those associated with the 2007 eruption (Miyaoka and Takagi, 2016).…”

“…Stacking of GNSS data revealed that a small volume change occurred immediately beneath the summit from 1 month prior to the eruption, as well as a small volume increase at depth from 1.5 months before the eruption (Miyaoka and Takagi, 2016). These volume increases were much smaller than those associated with the 2007 eruption (Miyaoka and Takagi, 2016). A very long period (VLP) seismic event occurred 25 s before the eruption, suggesting that preexisting volcanic-tectonic faults ruptured immediately prior to the eruption at depths of 300-1000 m .…”

“…The relatively rapid rate of chemical diffusion in Fe-Ti oxides (Nakamura, 1995;Venezky and Rutherford, 1999) and the small amount of ground deformation prior to the 2014 eruption Miyaoka and Takagi, 2016;Takagi and Onizawa, 2016) indicate that the observed wide range of temperatures (700-1300°C, but likely 700-950°C) reflect derivation of material from a thermally heterogeneous, near-solid, to partially molten magma body.…”

Hidden pressurized fluids prior to the 2014 phreatic eruption at Mt Ontake

“…The former would be identified too late in issuing a successful warning while the long-term precursors are based on data too sparse to be useful for near-real-time forecasting 6 . Some mid-term precursors (days to 1 month) were highlighted by re-examining geodetic 9 and seismic data 10 . The ground uplift from geodetic data remained ambiguous, whereas the deviation of the local stress field from seismic data 10 would practically be difficult to implement in most volcano observatories.…”