DOCSLIB.ORG

Monitoring Eruption Activity Using Temporal Stress Changes at Mount Ontake Volcano

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Monitoring Eruption Activity Using Temporal Stress Changes at Mount Ontake Volcano ARTICLE Received 27 Jul 2015 | Accepted 21 Jan 2016 | Published 19 Feb 2016 DOI: 10.1038/ncomms10797 OPEN Monitoring eruption activity using temporal stress changes at Mount Ontake volcano Toshiko Terakawa1, Aitaro Kato1, Yoshiko Yamanaka1, Yuta Maeda1, Shinichiro Horikawa1, Kenjiro Matsuhiro1 & Takashi Okuda1 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. 1 Earthquake and Volcano Research Center, Graduate School of Environmental Studies, Nagoya University, D2-2 (510) Furo-cho Chikusa-ku, Nagoya 464-8601, Japan. Correspondence and requests for materials should be addressed to T.T. (email: [email protected]). NATURE COMMUNICATIONS | 7:10797 | DOI: 10.1038/ncomms10797 | www.nature.com/naturecommunications 1 ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms10797 he local stress field around volcanoes represents the reaching a peak on 11 September 2014 before decaying over time superposition of the regional stress field and stress until the eruption, although the seismicity increased again Tperturbations related to volcanic activity1–4. Temporal between 15 and 21 September 2014 during this period. stress changes over periods of weeks to months are generally Long-period earthquakes with peak frequencies of 1–5 Hz were attributed to volcanic processes. Examining the focal mechanism recorded beginning around 15 September, but less than 10 solutions of volcano-tectonic (VT) earthquakes provides detailed long-period events were detected in real time. Application of a information on the state of a volcano via the local stress field. This matched-filter technique to continuous waveforms (23 August to has the potential to contribute to prediction of eruptions over the 30 September 2014) resulted in detection of thousands of micro- short and medium term (weeks to months). seismic events, indicating that an increase in VT events was Mt. Ontake volcano is the second highest stratovolcano in followed by an increase in the number of long-period events 5 Japan and is located at the southern end of the Northern Japan days later6. This detailed analysis also revealed that VT events Alps. On 27 September 2014, around 11:52 hours JST (UTC þ 9), beneath the craters migrated upwards as well as laterally in the Mt. Ontake produced a hydrothermal (steam-type) eruption with NNW–SSE direction for the final 10 min preceding the eruption6. a volcanic explosivity index (VEI) value of 2 (ref. 5). Mt. Ontake The phenomenon synchronized with a rapid increase of pre- had been considered dormant until its first historical eruption in eruptive tremor amplitudes and with an unusual tiltmeter signal October 1979. The 2014 eruption struck on a sunny Saturday in indicating summit upheaval6. After the eruption, the magnitudes the autumn foliage season, resulting in the worst volcanic disaster of events became larger (Mo1); in contrast, most pre-eruption in Japan in the last 90 years: 58 people died and 5 are still missing. events had a magnitude of less than 0. Mt. Ontake is continuously monitored by several relatively The time history of volcanic earthquakes during the pre- dense networks of permanent seismic stations operated by eruption period was explained by the generic volcanic earthquake Nagoya University, Japan Meteorological Agency (JMA), swarm model7. In this respect, the history was similar to that National Research Institute for Earth Science and Disaster associated with a previous minor eruption in 2007 (VEI ¼ 0)8. Prevention (NIED), and Gifu and Nagano prefectures However, unlike the 2007 eruption, the 2014 eruption was not (Fig. 1a,b). The summit region of Mt. Ontake (Fig. 1a,b; latitude preceded by active volcanic tremors and inflation of the volcanic 35.875° N–35.900° N, longitude 137.44° E–137.50° E) is normally edifice until 7 min before the eruption6,9. The time scale for the almost aseismic, with an average of less than one event (Mo0) precursor period was also different from that in 2007. In general, per month, whereas the surrounding region is characterized by a the various observations of precursor processes make eruption high level of background seismicity (see Methods). The onset of forecasting difficult, although changes in volcanic seismicity have VT earthquakes was observed on 31 August 2014 (Fig. 1b,c), been successfully used empirically for predicting eruptions10,11. ab137.4° 137.5° 35.95° M 2 1,000 1,000 M 1 M 0 1,000 2,000 M −1 1,000 M −2 2,000 1,000 36.2° 1,000 2,000 2,000 2,000 35.90° 1,000 2,000 1,000 1,000 2,000 1,000 (km) 1,000 1,000 2,000 1,000 36.0° 1,000 1,000 0 1 2 1,000 1,000 35.85° 1,000 1,000 2,000 1,000 –2 0 2 4 6 1,000 2,000 1,000 Depth (km) 1,000 1,000 2,000 1,000 1,000 c 35.8° Eruption 1,000 400 1,000 2,000 1,000 1,000 2,000 300 1,000 1,000 M3 (km) 1,000 M2 M1 01020 M0 200 35.6° 137.2° 137.6° 138.0° 100 Number of events 0 0152053010 25 9/1 11 21 10/1 11 21 31 Depth (km) Year 2014 Figure 1 | Seismicity around Mount Ontake. (a) Earthquake hypocentres and seismic stations in the Ontake region and (b) summit region. The circles denote hypocentres, and the colour scale corresponds to focal depth. The light blue, grey and black squares denote seismic stations operated by the Nagoya University, the national institutes and prefectural institutes, respectively. The blue rectangle in the inset in a shows the location of the Ontake region. The triangle, star, red rectangles and pink rectangle denote Mt. Ontake, the hypocentre of the 1984 Western Nagano Prefecture Earthquake, the summit region and the region depicted in Fig. 3b, respectively. The black dashed lines in a,b indicate the boundary between Nagano and Gifu prefectures. (c) Histogram of VT events per day in the summit region. 2 NATURE COMMUNICATIONS | 7:10797 | DOI: 10.1038/ncomms10797 | www.nature.com/naturecommunications NATURE COMMUNICATIONS | DOI: 10.1038/ncomms10797 ARTICLE The local stress field beneath volcanoes is directly influenced a Eruption by the inflation of the ascending magma and magmatic/ 16 Before the eruption After the eruption Normal 1–4 6 hydrothermal fluids . As the focal mechanism solution of VT 14 % Strike-slip 23 % Reverse 29 % 24 % events contains information on the local stress field, the 52 % Odd 12 10% 41 % relationships between stresses and volcanic processes have been 10 14% studied by examining focal mechanisms and using theoretical 8 models with the aim to successfully predict eruptions1–4,12–17. However, systematic spatiotemporal changes in focal mechanisms 6 4 do not necessarily indicate changes in the stress field18, because Number of events earthquakes can be triggered at faults that are misoriented to the 2 stress field by a decrease in fault strength caused by an increase in 0 pore fluid pressure19,20. This effect cannot be ignored when 9/1 10/1 11/1 12/1 1/1 2/1 3/1 Year 2015 evaluating the local stress fields beneath active volcanoes because Year 2014 the existence of over-pressurized fluids is certain. b 60 35.90° 0 Here we propose a method to detect true temporal changes in (km) 31/08/2014−27/09/2014:11:502,400 the local stress field beneath Mt. Ontake by examining the focal 0 1 3,000 2,200 mechanism solutions of VT events relative to the regional stress 3,000 pattern. Enhanced volcanic activity causes significant stress 35.89° perturbation with E–W tension, using the crustal structure 2,600 2,800 controlled by the regional stress field. This results in a large M 1.0 35.88° 2,400 deviation of the local stress field from the regional stress field 2,600 M 0.0 before the 2014 eruption. We demonstrate that quantitative M −0.5 evaluation of temporal stress changes is an effective tool for c 60 eruption monitoring. 0 35.90° (km) 27/09/2014:11:50−31/10/20142,400 0 1 Misfit angles 3,000 2,200 180° Results 3,000 Focal mechanism solutions of VT earthquakes. We estimated 35.89° the focal mechanism solutions of 94 VT earthquakes in the 2,600 90° summit region (August 2014 to March 2015) from S:P amplitude 2,800 35.88° 2,400 ratios and P wave polarity data obtained through the dense 2,600 21 seismic networks (Fig. 1a) using the HASH software package .In 0° the analysis, we assumed that the source was double couple (DC) 137.44° 137.46° 137.48° 137.50° and considered three velocity models (Supplementary Fig. 1) to Figure 2 | Temporal changes in focal mechanism solutions. account for possible errors in the hypocentres and take-off angles (a) Classification of focal mechanism solutions22.
Load more

Recommended publications
  • The Phreatic Eruption of Mt. Ontake Volcano in 2014 Editorial Board (December 2016) Editor-In-Chief Yasuo Ogawa, Tokyo Institute of Technology, Japan
    The Phreatic Eruption of Mt. Ontake Volcano in 2014 Editorial Board (December 2016) Editor-in-Chief Yasuo Ogawa, Tokyo Institute of Technology, Japan Vice Editors-in-Chief Masato Furuya, Hokkaido University, Japan Nozomu Nishitani, Nagoya University, Japan Solid Earth Science Space Science Editors Yosuke Aoki Huixin Liu Takeshi Sakanoi Nanan Balan Takuto Maeda Martha K. Savage Stephen Bannister Koji Matsumoto Benoit Taisne Shanaka de Silva Mitsuhiro Nakagawa Hiroshi Takenaka Koji Fukuma Junichi Nakajima Hiroaki Toh Lin-Ni Hau Yasuhiro Nariyuki Yih-Min Wu Hauke Hussmann Azusa Nishizawa Akimasa Yoshikawa Attila Komjathy Keiji Ohtsuki Alexey Kuvshinov Taku Ozawa Advisory Board Benjamin Fong Chao Hiroo Kanamori Toshitaka Tsuda Bernard Chouet Jun'ichiro Kawaguchi Zhongliang Wu Yoshimori Honkura Takafumi Matsui Kiyoshi Yomogida Toshihiko Iyemori Hitoshi Mizutani Journal Scope Earth, Planets and Space (EPS) is the official journal of the Society of Geomagnetism and Earth, Planetary and Space Sciences, The Seismological Society of Japan, The Volcanological Society of Japan, The Geodetic Society of Japan, and The Japanese Society for Planetary Sciences. EPS is a peer-reviewed, open-access journal published under SpringerOpen. It is an international journal covering scientific articles in the entire field of earth and planetary sciences, particularly geomagnetism, aeronomy, space science, seismology, volcanology, geodesy, and planetary science. EPS also welcomes articles in new and interdisciplinary subjects, and technical reports on instrumentation and software. The journal was launched in 1998 and has since published over 2700 articles. All of them are available for free on SpringerLink: http://link.springer.com/journal/40623 More information about the journal, its article collections, and the submission process is available on the journal homepage: http://earth-planets-space.springeropen.com Submit your next research article to Earth, Planets and Space via: https://www.editorialmanager.com/epsp Yours sincerely, Prof.
    [Show full text]
  • Sulfur Isotopic Characteristics of Volcanic Products from the September 2014 Mount Ontake Eruption, Japan
    Sulfur isotopic characteristics of volcanic products from the September 2014 Mount Ontake eruption, Japan 著者 Ikehata Kei, Maruoka Teruyuki journal or Earth, planets and space publication title volume 68 number 1 page range 116 year 2016-07 権利 (C) 2016 The Author(s). This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. URL http://hdl.handle.net/2241/00143733 doi: 10.1186/s40623-016-0496-z Creative Commons : 表示 http://creativecommons.org/licenses/by/3.0/deed.ja Ikehata and Maruoka Earth, Planets and Space (2016) 68:116 DOI 10.1186/s40623-016-0496-z LETTER Open Access Sulfur isotopic characteristics of volcanic products from the September 2014 Mount Ontake eruption, Japan Kei Ikehata* and Teruyuki Maruoka Abstract Components and sulfur isotopic compositions of pyroclastic materials from the 2014 Mt. Ontake eruption were inves- tigated. The volcanic ash samples were found to be composed of altered volcanic fragments, alunite, anhydrite, bio- tite, cristobalite, gypsum, ilmenite, kaolin minerals, native sulfur, orthopyroxene, plagioclase, potassium feldspar, pyrite, pyrophyllite, quartz, rutile, and smectite, and most of these minerals were likely derived from the acidic alteration zones of Mt. Ontake. The absence of juvenile material in the eruptive products indicates that the eruption was phre- atic. The sulfur isotopic compositions of the water-leached sulfate, hydrochloric acid-leached sulfate, acetone-leached native sulfur, and pyrite of the samples indicate that these sulfur species were produced by disproportionation of magmatic SO2 in the hydrothermal system at temperatures of 270–281 °C.
    [Show full text]
  • 6. Research Contributions 6.1 Outline of Research Contributions
    6. Research Contributions 6.1 Outline of Research Contributions Published papers are classified as follows: Average umbers of papers for one researcher are as (A) refereed papers, follows; (B) research reviews, (A) 10.43 (previous review 5.68) (C) books, (A1) 4.89 (previous review 2.60) (D) research papers in bulletins and reports, (A2) 3.76 (previous review 2.23) (E) textbooks for lectures, (A3) 1.78 (previous review 0.85) (F) articles in newspapers and magzines, Papers of all categories have increased, in particular, (G) non-refereed papers, papers in (A1) increased by about 30%, considering the (H) data acquisition and collection reports. periods of collections. This indicates that many researchers are conscious of the importance of publishing papers in The refereed papers (A) are subdivided into three refereed journals. 57% of the refreed papers (A) were categories; (A1) complete refereed papers, which are usual written in English. refereed papers published in the scientific or technical In 2001, a book, ‘Handbook of Disaster Prevention journals. (A2) refereed papers, which are refereed papers ‘ was published as a memorial publication of the Disaster read at scientific meetings. (A3) abstract refereed papers, Prevention Research Institute. Besides, lectures to peoples of which abstracts are refereed. The papers in (G) are also were initiated as part of the 21st Century COE (Center Of subdivided into two categories; (G1) papers presented at Excellence) Program. It is quite important to inform the meetings or conferences and (G2) non-refreed papers public of recent research results to popularize knowledge published in academic journals. of disaster mitigation.
    [Show full text]
  • Reconstruction of a Phreatic Eruption on 27 September 2014 at Ontake
    Maeno et al. Earth, Planets and Space (2016) 68:82 DOI 10.1186/s40623-016-0449-6 FULL PAPER Open Access Reconstruction of a phreatic eruption on 27 September 2014 at Ontake volcano, central Japan, based on proximal pyroclastic density current and fallout deposits Fukashi Maeno1*, Setsuya Nakada1, Teruki Oikawa2, Mitsuhiro Yoshimoto3, Jiro Komori4, Yoshihiro Ishizuka2, Yoshihiro Takeshita5, Taketo Shimano6, Takayuki Kaneko1 and Masashi Nagai7 Abstract The phreatic eruption at Ontake volcano on 27 September 2014, which caused the worst volcanic disaster in the past half-century in Japan, was reconstructed based on observations of the proximal pyroclastic density current (PDC) and fallout deposits. Witness observations were also used to clarify the eruption process. The deposits are divided into three major depositional units (Units A, B, and C) which are characterized by massive, extremely poorly sorted, and multimodal grain-size distribution with 30–50 wt% of fine ash (silt–clay component). The depositional condition was initially dry but eventually changed to wet. Unit A originated from gravity-driven turbulent PDCs in the relatively dry, vent-opening phase. Unit B was then produced mainly by fallout from a vigorous moist plume during vent develop- ment. Unit C was derived from wet ash fall in the declining stage. Ballistic ejecta continuously occurred during vent opening and development. As observed in the finest population of the grain-size distribution, aggregate particles were formed throughout the eruption, and the effect of water in the plume on the aggregation increased with time and distance. Based on the deposit thickness, duration, and grain-size data, and by applying a scaling analysis using a depth-averaged model of turbulent gravity currents, the particle concentration and initial flow speed of the PDC 4 3 at the summit area were estimated as 2 10− –2 10− and 24–28 m/s, respectively.
    [Show full text]
  • List of Volcanoes in Japan
    Elevation Elevation Sl. No Name Prefecture Coordinates Last eruption Meter Feet 1 Mount Meakan Hokkaidō 1499 4916 43.38°N 144.02°E 2008 2 Mount Asahi (Daisetsuzan) Hokkaidō 2290 7513 43.661°N 142.858°E 1739 3 Lake Kuttara Hokkaidō 581 1906 42.489°N 141.163°E - 4 Lake Mashū Hokkaidō 855 2805 43.570°N 144.565°E - 5 Nigorigawa Hokkaidō 356 1168 42.12°N 140.45°E Pleistocene 6 Nipesotsu-Maruyama Volcanic Group Hokkaidō 2013 6604 43.453°N 143.036°E 1899 7 Niseko Hokkaidō 1154 3786 42.88°N 140.63°E 4050 BC 8 Oshima Hokkaidō 737 2418 41.50°N 139.37°E 1790 9 Mount Rausu Hokkaidō 1660 5446 44.073°N 145.126°E 1880 10 Mount Rishiri Hokkaidō 1721 5646 45.18°N 141.25°E 5830 BC 11 Shikaribetsu Volcanic Group Hokkaidō 1430 4692 43.312°N 143.096°E Holocene 12 Lake Shikotsu Hokkaidō 1320 4331 42.70°N 141.33°E holocene 13 Mount Shiretoko Hokkaidō 1254 4114 44°14′09″N 145°16′26″E 200000 BC 14 Mount Iō (Shiretoko) Hokkaidō 1563 5128 44.131°N 145.165°E 1936 15 Shiribetsu Hokkaidō 1107 3632 42.767°N 140.916°E Holocene 16 Shōwa-shinzan Hokkaidō 731 2400 42.5°N 140.8°E 1945 17 Mount Yōtei Hokkaidō 1898 6227 42.5°N 140.8°E 1050 BC 18 Abu (volcano) Honshū 571 - 34.50°N 131.60°E - 19 Mount Adatara Honshū 1718 5635 37.62°N 140.28°E 1990 20 Mount Akagi Honshū 1828 5997 36.53°N 139.18°E - 21 Akita-Komaga-Take Honshū 1637 5371 39.75°N 140.80°E 1971 22 Akita-Yake-Yama Honshū 1366 4482 39.97°N 140.77°E 1997 23 Mount Asama Honshū 2544 8340 36.24°N 138.31°E 2009 24 Mount Azuma Honshū 1705 5594 37.73°N 140.25°E 1977 25 Mount Bandai Honshū 1819 5968 37.60°N 140.08°E 1888
    [Show full text]
  • Reconstruction of the 2014 Eruption Sequence of Ontake Volcano From
    Oikawa et al. Earth, Planets and Space (2016) 68:79 DOI 10.1186/s40623-016-0458-5 FULL PAPER Open Access Reconstruction of the 2014 eruption sequence of Ontake Volcano from recorded images and interviews Teruki Oikawa1*, Mitsuhiro Yoshimoto2, Setsuya Nakada3, Fukashi Maeno3, Jiro Komori4, Taketo Shimano5, Yoshihiro Takeshita6, Yoshihiro Ishizuka1 and Yasuhiro Ishimine7 Abstract A phreatic eruption at Mount Ontake (3067 m) on September 27, 2014, led to 64 casualties, including missing people. In this paper, we clarify the eruption sequence of the 2014 eruption from recorded images (photographs and videos obtained by climbers) and interviews with mountain guides and workers in mountain huts. The onset of eruption was sudden, without any clear precursory surface phenomena (such as ground rumbling or strong smell of sulfide). Our data indicate that the eruption sequence can be divided into three phases. Phase 1: The eruption started with dry pyroclastic density currents (PDCs) caused by ash column collapse. The PDCs flowed down 2.5 km SW and 2 km NW from the craters. In addition, PDCs moved horizontally by approximately 1.5 km toward N and E beyond summit ridges. The temperature of PDCs at the summit area partially exceeded 100 °C, and an analysis of interview results suggested that the temperature of PDCs was mostly in the range of 30–100 °C. At the summit area, there were violent falling ballistic rocks. Phase 2: When the outflow of PDCs stopped, the altitude of the eruption column increased; tephra with muddy rain started to fall; and ambient air temperature decreased. Falling ballistic rocks were almost absent during this phase.
    [Show full text]
  • Volcanic Plume Measurements Using a UAV for the 2014 Mt. Ontake
    Mori et al. Earth, Planets and Space (2016) 68:49 DOI 10.1186/s40623-016-0418-0 FULL PAPER Open Access Volcanic plume measurements using a UAV for the 2014 Mt. Ontake eruption Toshiya Mori1* , Takeshi Hashimoto2, Akihiko Terada3, Mitsuhiro Yoshimoto4, Ryunosuke Kazahaya5, Hiroshi Shinohara5 and Ryo Tanaka6 Abstract A phreatic eruption of Mt. Ontake, Japan, started abruptly on September 27, 2014, and caused the worst volcanic calamity in recent 70 years in Japan. We conducted volcanic plume surveys using an electric multirotor unmanned aerial vehicle to elucidate the conditions of Mt. Ontake’s plume, which is flowing over 3000 m altitude. A plume gas composition, sulfur dioxide flux and thermal image measurements and a particle sampling were carried out using the unmanned aerial vehicle for three field campaigns on November 20 and 21, 2014, and June 2, 2015. Together with the results of manned helicopter and aircraft observations, we revealed that the plume of Mt. Ontake was not directly emitted from the magma but was influenced by hydrothermal system, and observed SO2/H2S molar ratios were decreasing after the eruption. High SO2 flux of >2000 t/d observed at least until 20 h after the onset of the eruption implies significant input of magmatic gas and the flux quickly decreased to about 130 t/d in 2 months. In contrast, H2S fluxes retrieved using SO2/H2S ratio and SO2 flux showed significantly high level of 700–800 t/d, which continued at least between 2 weeks and 2 months after the eruption. This is a peculiar feature of the 2014 Mt.
    [Show full text]
  • Lahar Characteristics As a Function of Triggering Mechanism at A
    Kataoka et al. Earth, Planets and Space (2018) 70:113 https://doi.org/10.1186/s40623-018-0873-x FULL PAPER Open Access Lahar characteristics as a function of triggering mechanism at a seasonally snow‑clad volcano: contrasting lahars following the 2014 phreatic eruption of Ontake Volcano, Japan Kyoko S. Kataoka1*, Takane Matsumoto1, Takeshi Saito2, Katsuhisa Kawashima1, Yoshitaka Nagahashi3, Tsutomu Iyobe4, Akihiko Sasaki5,6 and Keisuke Suzuki5 Abstract In association with the September 2014 phreatic eruption (VEI 1–2) at Ontake Volcano, a syn-eruptive and two post-eruptive lahars occurred in the Akagawa–Nigorigawa River, southern fank of the volcano. The present contribu- tion describes and discusses the contrasting features of the two post-eruptive lahars, which caused a major impact on downstream river morphology, and re-examines the description of the syn-eruptive lahar in the previous study. The frst post-eruptive lahar occurred 8 days after the eruption by the rainstorm (October 5, 2014, before the snowy season), and the second lahar was associated with the rain-on-snow (ROS) event on April 20, 2015, in the early spring of the snowmelt season. The October rain-triggered lahar, which can be interpreted as a cohesive debris fow, reached at least ~ 11 km downstream and left muddy matrix-rich sediments with high clay content (10–20 wt% of clay in matrix). The lahar deposits contain hydrothermally altered rock fragments, sulfde/sulfate minerals, and clay miner- als and show extremely high total sulfur content (10–14 wt%) in matrix part, indicating source material from the September phreatic eruption deposits.
    [Show full text]
  • Title: Locating Hydrothermal Fluid Injection of the 2018 Phreatic Eruption at Kusatsu
    Locating hydrothermal uid injection of the 2018 phreatic eruption at Kusatsu-Shirane volcano with volcanic tremor amplitude Taishi Yamada ( [email protected] ) Kyoto University https://orcid.org/0000-0002-5919-9195 Aika K Kurokawa National Research Institute for Earth Science and Disaster Resilience Akihiko Terada Volcanic Fluid Research Center, School of Science, Tokyo Institute of Technology Wataru Kanda Volcanic Fluid Research Center, School of Science, Tokyo Institute of Technology Hideki Ueda National Research Institute for Earth Science and Disaster Resilience Hiroshi Aoyama Institute of Seismology and Volcanology, Faculty of Science, Hokkaido University Takahiro Ohkura Aso Volcanological Laboratory, Kyoto University Yasuo Ogawa Volcanic Fluid Research Center, School of Science, Tokyo Institute of Technology Toshikazu Tanada National Research Institute for Earth Science and Disaster Resilience Full paper Keywords: Kusatsu-Shirane, Phreatic eruptions, Volcanic tremor, Hydrothermal system Posted Date: September 16th, 2020 DOI: https://doi.org/10.21203/rs.3.rs-74868/v1 License: This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License Version of Record: A version of this preprint was published on January 11th, 2021. See the published version at https://doi.org/10.1186/s40623-020-01349-1. Title: Locating hydrothermal fluid injection of the 2018 phreatic eruption at Kusatsu- Shirane volcano with volcanic tremor amplitude Author #1: Taishi Yamada, Sakurajima Volcano Research
    [Show full text]
  • Preparatory Process Preceding the 2014
    Murase et al. Earth, Planets and Space (2016) 68:9 DOI 10.1186/s40623-016-0386-4 FULL PAPER Open Access Preparatory process preceding the 2014 eruption of Mount Ontake volcano, Japan: insights from precise leveling measurements Masayuki Murase1*, Fumiaki Kimata2, Yoshiko Yamanaka3, Shinichiro Horikawa3, Kenjiro Matsuhiro3, Takeshi Matsushima4, Hitoshi Mori5, Takahiro Ohkura6, Shin Yoshikawa6, Rikio Miyajima2, Hiroyuki Inoue6, Taketoshi Mishima6, Tadaomi Sonoda7, Kazunari Uchida4, Keigo Yamamoto7 and Harushisa Nakamichi7 Abstract Preparatory activity preceding the 2014 eruption of Mount Ontake volcano was estimated from vertical deformation detected using a precise leveling survey. Notable uplift (2006–2009) and subsidence (2009–2014) were detected on the eastern flank of the volcano. We estimated pressure source models based on the vertical deformation and used these to infer preparatory process preceding the 2014 eruption. Our results suggest that the subsidence experienced between 2009 and 2014 (including the period of the 2014 eruption) occurred as a result of a sill-like tensile crack with a depth of 2.5 km. This tensile crack might inflate prior to the eruption and deflate during the 2014 activity. A two-tensile-crack model was used to explain uplift from 2006 to 2009. The geometry of the shallow crack was assumed to be the same as the sill-like tensile crack. The deep crack was estimated to be 2 km in length, 4.5 km in width, and 3 km in depth. Distinct uplifts began on the volcano flanks in 2006 and were followed by seismic activities and a small phreatic eruption in 2007. From the partially surveyed leveling data in August 2013, uplift might continue until August 2013 without seismic activity in the summit area.
    [Show full text]
  • Anatomy of Active Volcanic Edifice at the Kusatsu–Shirane Volcano
    Tseng et al. Earth, Planets and Space (2020) 72:161 https://doi.org/10.1186/s40623-020-01283-2 EXPRESS LETTER Open Access Anatomy of active volcanic edifce at the Kusatsu–Shirane volcano, Japan, by magnetotellurics: hydrothermal implications for volcanic unrests Kuo Hsuan Tseng1, Yasuo Ogawa2* , Nurhasan1,3, Sabri Bülent Tank1,4, Naoto Ujihara1,5, Yoshimori Honkura2, Akihiko Terada2, Yoshiya Usui1,6 and Wataru Kanda2 Abstract We aimed to perform three-dimensional imaging of the underlying geothermal system to a depth of 2 km using magnetotellurics (MT) at around the Yugama crater, the Kusatsu–Shirane Volcano, Japan, which is known to have frequent phreatic eruptions. We deployed 91 MT sites focusing around the peak area of 2 km 2 km with typical spacings of 200 m. The full tensor impedances and the magnetic transfer functions were inverted,× using an unstruc- tured tetrahedral fnite element code to include the topographic efect. The fnal model showed (1) low-permeability bell-shaped clay cap (C1) as the near-surface conductor, (2) brine reservoir as a deep conductor (C3) at a depth of 1.5 km from the surface, and (3) a vertical conductor (C2) connecting the deep conductor to the clay cap which implies an established fuid path. The columnar high-seismicity distribution to the east of the C2 conductor implies that the fushed vapor and magmatic gas was released from the brine reservoir by breaking the silica cap at the brit- tle–ductile transition. The past magnetization/demagnetization sources and the infation source of the 2014 unrest are located just below the clay cap, consistent with the clay capped geothermal model underlain by brine reservoir.
    [Show full text]
  • Preparatory and Precursory Processes Leading up to the 2014 Phreatic
    Kato et al. Earth, Planets and Space (2015) 67:111 DOI 10.1186/s40623-015-0288-x FRONTIER LETTER Open Access Preparatory and precursory processes leading up to the 2014 phreatic eruption of Mount Ontake, Japan Aitaro Kato1,2*, Toshiko Terakawa1, Yoshiko Yamanaka1, Yuta Maeda1, Shinichiro Horikawa1, Kenjiro Matsuhiro1 and Takashi Okuda1 Abstract We analyzed seismicity linked to the 2014 phreatic eruption of Mount Ontake, Japan, on 27 September 2014. We first relocated shallow volcano tectonic (VT) earthquakes and long-period (LP) events from August to September 2014. By applying a matched-filter technique to continuous waveforms using these relocated earthquakes, we detected numerous additional micro-earthquakes beneath the craters. The relocated VT earthquakes aligned on a near-vertical plane oriented NNW–SSE, suggesting they occurred around a conduit related to the intrusion of magmatic–hydrothermal fluids into the craters. The frequency of VT earthquakes gradually increased from 6 September 2014 and reached a peak on 11 September 2014. After the peak, seismicity levels remained elevated until the eruption. b-values gradually increased from 1.2 to 1.7 from 11 to 16 September 2014 then declined gradually and dropped to 0.8 just before the eruption. During the 10-min period immediately preceding the phreatic eruption, VT earthquakes migrated in the up-dip direction as well as laterally along the NNW–SSE feature. The migrating seismicity coincided with an accelerated increase of pre-eruptive tremor amplitude and with an anomalous tiltmeter signal that indicated summit upheaval. Therefore, the migrating seismicity suggests that the vertical conduit was filled with pressurized fluids, which rapidly propagated to the surface during the final 10 min before the eruption.
    [Show full text]