Search

We conducted an active seismic experiment in Sakurajima volcano in December 2019, three years after the similar experiment that was conducted in 2016. We deployed 185 temporary seismic stations, most of which were installed at the same place as in 2013 and 2016. Eight and two explosive shots with 20 and 100 kg charges, respectively, were detonated in December 5, 2019. The 2019 shot locations differ from 0.4 to 12 m from the corresponding previous shot locations. We successively observed the all explosions during nighttime nine hours continuous recording. We examine reflection phases on the seismic records that obtained by the previous and 2019 experiment to detect temporal change of subsurface seismic structure beneath Sakurajima volcano.

Additional file 1. Discussion of Peacock et al. (2012)’s and Heise et al. (2007, 2008)’s phase tensor residual ellipse natures in a large phase tensor ellipticity case.

Additional file 3. Comparisons between the electrical resistivity and seismic velocity models. Figure S3.1: Plan or map view of the Vp model by Okada et al. (2015) superimposed on the resistivity model (Fig. 5). The white lines are Vp contours with the interval of 0.1 km/s. The background color represents the logarithmic resistivity value. The black and white circles, red character, and black triangles, are observation sites, sampling point of Vp model, Oana Crater, and edifice summits, respectively. The labels A and B for the conductors are referred to in the main text. Figure S3.2: Vertical profiles of the Vp model by Okada et al. (2015) superimposed on the resistivity model (Fig. 6) in the E-W direction. The white lines and circles are Vp contours and sampling point of the Vp model. Other features are the same as those in Fig. 6. Figure S3.3: Vertical profiles of the Vp model by Okada et al. (2015) superimposed on the resistivity model (Fig. 7) in the N-S direction. Other features are the same as those in Figs. 7 and S3.2. Figure S3.4: Plan or map view of the Vp/Vs distribution superimposed on the resistivity model (Fig. 5). The white lines are Vp/Vs contours with the interval of 0.025. The background color represents the logarithmic resistivity value. The black and white circles, red character, and black triangles, are observation sites, sampling point of Vp and Vs models, Oana Crater, and edifice summits, respectively. The label A and B for the conductors are referred to in the main text. Figure S3.5: Vertical profiles of the Vp/Vs distribution superimposed on the resistivity model (Fig. 6) in the E-W direction. The white lines and circles are Vp/Vs contours and sampling point of the Vp and Vs model. Other features are the same as those in Figures 6. Figure S3.6: Vertical profiles of the Vp/Vs distribution superimposed on the resistivity model (Fig. 7) in the N-S direction. Other features are the same as those in Figures 7 and S3.4.

Additional file 2. Comparisons between the observed and calculated MT, GDS responses. Figure S2.1: Map of site number for Figure S2.2. Figure S2.2: MT apparent resistivity and phase responses of each site. Top left number is site number as is shown in Figure S2.1. Observed responses of each component are represented by each character in the legend. Solid curves represent calculated responses with the final resistivity model (Figs. 5 to 7). Figure S2.3: Observed (left column), calculated (center column), and difference between the observed and calculated (right column) in-phase Parkinson vectors (Equation 11) at each site and various period or frequency. The calculated vector is obtained with the final resistivity model (Figs. 5 to 7). Figure S2.4: Observed (left column), calculated (center column), and difference between the observed and calculated (right column) quadrature-phase Parkinson vectors (Equation 12) at each site and various period or frequency. The calculated vector is obtained with the final resistivity model (Figs. 5 to 7).

Additional file 2: Figure S2.Inflation source during the 2014 unrest of the SPCG from March 2014 to October 2015. Optimal crack parameters are summarized at lower right in the figure. We searched for the best-fit combination of four parameters (Z, L, A, and U), assuming a sill-like source (D = 0°) and L/W = 2. The latitude and longitude of the center of the sill were fixed at 36.645° and 138.538°, respectively, representing the center of Mizugama crater. In this analysis, the smallest misfit (root mean square sum of the difference between the observed and calculated values of each tilt vector, and each uplift at KSYG (44 mm) and KSE (25 mm) measured by GNSS) was calculated by the grid-search method as described in Section “Modeling”. The optimal length (L), width (W), and dislocation (U) were 480 m, 240 m (assumed as half of the horizontal length), and 1.00 m, respectively, which resulted in a calculated volumetric expansion of ~1.2 × 105 m3.