Seismic structure and its implication on the hydrothermal system beneath Mt. Ontake, central Japan

Abstract

AbstractMt. Ontake is an active volcano in central Japan where phreatic eruption activity is prominent. A shallow subsurface structure in the summit region of this volcano has been scarcely studied despite its importance. Our study examines the structure from three seismic analyses: a typical P-wave velocity from the semblance of the vertical propagation of intermediate-depth earthquakes (IDEs), a layered velocity model from P- and S-wave arrival times of shallow volcanic earthquakes, and a pseudoreflection profile from the autocorrelation functions of the IDEs. Our results consistently indicate the presence of three layers, which are interpreted as younger (> 0.1 Ma) and older (0.39–0.78 Ma) eruptive deposits and the basement. A comparison of the structure with hypocentres and deformation sources suggests fluid migration controlled by the structure. Graphical Abstract