Seismic campaign in Showa-Shinzan lava dome in Usu Volcano, Northern Japan

Slides on seismic campaign in Usu Volcano to investigate the internal structure of the Showa Shinzan lava dome that emerge during the 1943-1945 eruption. They are prepared for an informal meeting at ISTerre, but not used.

Transcript

1. Seismic campaign in Showa- Shinzan lava dome in Usu Volcano, Northern Japan 1 October, 2019 ISTerre, France A. Takeo1, K. Nishida1, Y. Aoki1, H. Aoyama2, M. Ishise1, T. Maeda3, Y. Mizutani1, T. Kai1, Y. Nakashima1, S. Nagahara1, R. Kurihara1, L. Ye4, X. Wang5, T. Akuhara1 1ERI, Univ. Tokyo, 2Hokkaido Univ., 3Hirosaki Univ. 4Sun Yat-sen Univ., 5Southwest Jiaotong Univ.
2. Internal structure of lava domes ( ) Y. Goto, J. McPhierJournal of Volcanology and Geothermal Research 84 1998 273–286 277 Fig. 4. View of the Momo-iwa dome from the west, showing the dome in cross-section. Large-scale banding is parallel to the hemispherical surface of the dome. Locations for Figs. 6, 7 and 8B are also shown. A sketch of this cross-section is given in Fig. 5. ( ) Y. Goto, J. McPhierJournal of Volcanology and Geothermal Research 84 1998 273–286 278 Fig. 5. Sketch of the internal structure of the Momo-iwa dome, showing the concentric structure consisting of a massive core, banded rim and brecciated border. Radial columnar joints are well developed through the massive core to the banded rim. ally decrease outwards in diameter, from 150–200 cm in the centre to 60–80 cm at the margin of the core. Table 1 XRF major-element chemical analysis of the Momo-iwa dome Momo-8 SiO 62.89 2 TiO 0.89 The dacite is porphyritic, with 5 vol.% plagio- Ž . clase phenocrysts -1 mm long and trace amounts Ž . Ž . of augite -0.5 mm and opaque -0.5 mm phe- Ž . nocrysts. The groundmass 95 vol.% shows a pi- lotaxitic texture dominated by plagioclase microlites Ž . Ž . 82 vol.% , pale brown glass 7 vol.% , opaque Ž . Ž . Ž minerals 3 vol.% , quartz 2 vol.% and augite 1 . vol.% . Although no macroscopic flow banding is present in the massive core, the plagioclase micro- Goto & McPhie (JVGR, 1998) In-situ observation of exposures can view only the shallowest part of the intruded lava.
3. Usu Volcano and Showa-Shinzan lava dome 1910 Activity time Eruptive Interval (yr) Location Eruption type Upheaval height (m) July ̶ Nov. 1910 57 North flank Phreatic 170 Dec. 1943 ̶ Sep. 1945 33 East flank Phreatomagmatic 280 Aug. 1977 ̶ Mar. 1982 32 Summit Phreatomagmatic 180 Mar. ̶ Aug. 2000 18 West flank Phreatomagmatic 80
4. A phreatomagmatic eruption in 2000 Showa Shinzan that emerged during the 1943-1945 eruption 280 m
5. Muon radiography + Gravity 1910 ਤ2. ࡾদμΠΞάϥϜͱ ོىதͷՐޱࣸਅ(ࡾদ2004; Ճච) ࢁ௖ !"# mod ਤ4. ີ౓ߏ଄(Nishiyama et al. 2017ΑΓ) ü High density at the core of the lava dome. ü Seismic velocity combined with density gives elastic constants, thus material properties.
6. Seismic campaign 1910 ü 22 1-Hz seismometers (7 on the summit, 10 on the flank, and 5 on the foot) ü Instrumental response pre-calibrated. ü Recorded ambient noise to infer the velocity structure ͯ࢑ఆ1࣍ݩ଎౓ߏ଄Λਪఆͨ͠ɻ ͷॱʹS೾଎౓͕଎͍͜ͱ͕Θ͔ͬͨɻ
7. CCs and phase velocities: Summit 1910 4Hz 2Hz 1Hz ࢁ௖෇ۙ ԰ࠜࢁ
8. CCs and phase velocities: flank 1910 4Hz 2Hz 1Hz ԰ࠜࢁ
9. CCs and phase velocities: foot 1910 ࢁ௖෇ۙ ࿢ ԰ࠜࢁ ਤ12. (ࠨ)3άϧʔϓͦΕͧ (ӈ)ඪߴΛͣΒͨ͠S 4Hz 2Hz 1Hz ࿢
10. Phase and S-wave velocities 1910 Red: Summit Green: Flank Blue: Foot
11. Some earthquake signals 1910 ෇ۙͷ஍தͰൃੜͨ͠ͱݟΒΕΔ௿प೾஍਒ͷ೾ܗ΋ಘΔ͜ͱ͕Ͱ͖ ·ͱΊɾࠓޙͷల๬ ਤ13. 2018/5/12 21:03:00͔Β1෼ؒͷ೾ܗ ʢՖՐʣ ਤ14. 2018/6/3 00:01:00͔Β1෼ؒͷ೾ܗ ʢࢁ௖͔Βॱʹฒ΂ͨ; ࢁ௖෇ۙͷ௿प೾஍਒ʁʣ ۙͷ஍தͰൃੜͨ͠ͱݟΒΕΔ௿प೾஍਒ͷ೾ܗ΋ಘΔ͜ͱ͕Ͱ͖ͨ ͱΊɾࠓޙͷల๬ ਤ13. 2018/5/12 21:03:00͔Β1෼ؒͷ೾ܗ ʢՖՐʣ ਤ14. 2018/6/3 00:01:00͔Β1෼ؒͷ೾ܗ ʢࢁ௖͔Βॱʹฒ΂ͨ; ࢁ௖෇ۙͷ௿प೾஍਒ʁʣ 1 min. 1 min. Firework Low-frequency earthquake near the summit Near the summit Far from the summit