Fig. 3: Seismic velocity combined with complementary observations.
From: Hidden pressurized fluids prior to the 2014 phreatic eruption at Mt Ontake
dv/v is estimated using daily ACF at station ONTA and inverting for a continuous velocity change time as in Brenguier et al.30 with a weighting coefficient of 100,000 (black line). The dv/v curve has been corrected for external perturbations due to rain and snow accumulation, following Wang et al.22. We have also smoothed the dv/v curve using a Hodrick Prescott filter63 with a factor of 10,000 (red line). The water level data (blue line) are from Koizumi et al.41. The sensor is located between MKO and MTB stations (GOT, blue square, Fig. 1). The spikes in July and August 2014 correspond to a period attributed to sensor problems41. The red vertical solid line indicates the 27 September 2014 eruption, whereas black vertical dashed lines correspond to local earthquakes detected by our study. Long Period (LP) and Volcano Tectonic (VT) catalogs shown as red and green dots from August onwards and are from Zhang and Wen44. Rain and snow data were recorded at the station located nearby ONTN between 2012–2014 (Fig. 1) to remove the seasonal component.
