title: Monitoring eruption activity using temporal stress changes at Mount Ontake volcano.
abstract: Volcanic activity is often accompanied by many small earthquakes. Earthquake focal mechanisms represent the fault orientation and slip direction, which are influenced by the stress field. Focal mechanisms of volcano-tectonic earthquakes provide information on the state of volcanoes via stresses. Here we demonstrate that quantitative evaluation of temporal stress changes beneath Mt. Ontake, Japan, using the misfit angles of focal mechanism solutions to the regional stress field, is effective for eruption monitoring. The moving average of misfit angles indicates that during the precursory period the local stress field beneath Mt. Ontake was deviated from the regional stress field, presumably by stress perturbations caused by the inflation of magmatic/hydrothermal fluids, which was removed immediately after the expulsion of volcanic ejecta. The deviation of the local stress field can be an indicator of increases in volcanic activity. The proposed method may contribute to the mitigation of volcanic hazards.
authors.affiliation: Earthquake and Volcano Research Center, Graduate School of Environmental Studies, Nagoya University, D2-2 (510) Furo-cho Chikusa-ku, Nagoya 464-8601, Japan.
authors.forename: Toshiko
authors.initials: T
authors.lastname: Terakawa
authors.affiliation: Earthquake and Volcano Research Center, Graduate School of Environmental Studies, Nagoya University, D2-2 (510) Furo-cho Chikusa-ku, Nagoya 464-8601, Japan.
authors.forename: Aitaro
authors.initials: A
authors.lastname: Kato
authors.affiliation: Earthquake and Volcano Research Center, Graduate School of Environmental Studies, Nagoya University, D2-2 (510) Furo-cho Chikusa-ku, Nagoya 464-8601, Japan.
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Yamanaka
authors.affiliation: Earthquake and Volcano Research Center, Graduate School of Environmental Studies, Nagoya University, D2-2 (510) Furo-cho Chikusa-ku, Nagoya 464-8601, Japan.
authors.forename: Yuta
authors.initials: Y
authors.lastname: Maeda
authors.affiliation: Earthquake and Volcano Research Center, Graduate School of Environmental Studies, Nagoya University, D2-2 (510) Furo-cho Chikusa-ku, Nagoya 464-8601, Japan.
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Horikawa
authors.affiliation: Earthquake and Volcano Research Center, Graduate School of Environmental Studies, Nagoya University, D2-2 (510) Furo-cho Chikusa-ku, Nagoya 464-8601, Japan.
authors.forename: Kenjiro
authors.initials: K
authors.lastname: Matsuhiro
authors.affiliation: Earthquake and Volcano Research Center, Graduate School of Environmental Studies, Nagoya University, D2-2 (510) Furo-cho Chikusa-ku, Nagoya 464-8601, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Okuda