S-wave modelling of the Showa-Shinzan lava dome in Usu Volcano, Northern Japan, from seismic observations

Abstract

Summary To obtain an internal S-wave velocity structure, we conducted a passive seismic campaign with 21 1-Hz seismometers on and around the Showa-Shinzan lava dome, which emerged during the 1943–1945 eruption of Usu Volcano, Japan. Before the campaign, we calibrated seismometers and found slight phase-response differences between seismometers of less than 1–2 degrees. After the campaign, we extracted seismic wavefield by taking cross-correlations of vertical-component ambient noise records between seismic sites. We developed a new method to measure phase velocities of the Rayleigh wave automatically by assuming layered structure and finally obtained one-dimensional S-wave velocity models in summit, roof and base regions. The obtained S-wave velocity right beneath the intruded lava dome is higher than that in surrounding areas by a few tens of percent down to a few hundred meters below sea level, indicating narrow but deep existence of the root of the lava dome. The obtained S-wave velocity at depths shallower than ∼50 m inside the lava dome in the summit area was ∼1 km/s, significantly lower than that predicted from the density of 2.3 × 103 kg/m3 estimated in previous muon-radiography studies and a conventional scaling, indicating the effect of cracking in the lava dome.

Seismic Structure of the Lithosphere‐Asthenosphere System Beneath the Oldest Seafloor Revealed by Rayleigh‐Wave Dispersion Analysis

“…Under this expression, however, unrealistic peaks and/or troughs are potentially introduced to the dispersion curve because of its dependency on the knot intervals. In order to introduce physically realizable constraints on the dispersion curve, we directly calculate the dispersion curves from an isotropic velocity model as for the cases of teleseismic waveforms (e.g., Takeo et al., 2018; Yoshizawa & Kennett, 2002) and the ambient noise on land (Takeo et al., 2022). The model has 14 layers of piecewise constant S‐wave velocity from the seafloor to the depth of 190 km.…”

Research on the prediction method of string-supported dome cable force based on digital twin technology

“…The string-supported dome structure, in which the tension cables are subjected to huge tensile forces, is the core component of the structure. In terrorist attacks, construction defects and other unexpected circumstances will occur the phenomenon of broken cables; the sudden breakage of the tension cable will produce a certain dynamic impact effect on the structure, causing the vibration of the nearby rod position [11][12][13]. The internal force changes and the sudden impact effect will make the internal force of the rod oscillate up and down substantially, and its magnitude can far exceed the original level, so the study of the dynamic impact effect of the broken cable is very important [14][15][16][17][18].…”