Fracture Structures in and Around Hakone Volcano Revealed by Dense Seismic Observations
Ryou Honda*,, Yuki Abe*, Yohei Yukutake**, and Shin’ichi Sakai***
*Hot Springs Research Institute of Kanagawa Prefecture (HSRI)
586 Iriuda, Odawara, Kanagawa 250-0031, Japan
**Earthquake Research Institute, The University of Tokyo, Tokyo, Japan
***Interfaculty Initiative in Information Studies, The University of Tokyo, Tokyo, Japan
Preexisting fracture systems, including old fissures, dikes, and microfractures in the caldera, are possibly used as channels for magma and hydrothermal fluid intrusions during an eruption. To reveal such a fracture system in the Hakone volcano, we used the fuzzy c-means method to perform clustering on S-wave splitting analysis results. The results show that the fracture system in the Hakone caldera can be divided into two clusters (A and B) or four clusters (A1, A2, B1, and B2). In the central cone vicinity, craters or dikes corresponding to the compressive axis of the regional stress field are dominant, whereas the fault systems with the best orientation to the regional stress field develop around the central cone. Cluster B1 can be explained by the northwest–southeast alignment of micro cracks or dikes corresponding to the direction of maximum horizontal pressure of the regional stress field. The others are likely explained by fault fracture zones, which have an optimal orientation for regional stress fields, or by the alignment of micro cracks affected by the local stress field. Cluster B2 suggests the existence of fracture zones of the Tanna and Hirayama fault systems, which cross the Hakone volcano from north to south. Clusters A1 and A2 are possibly explained by the conjugate system of B2. However, the alignment of micro cracks generated by the local stress field or old volcanic structures can also be a cause of the clusters.
-  M. Kobayashi, “Eruption history of the Hakone central cone volcanoes, and geographical development closely related to eruptive activity in the Hakone caldera,” Res. Rep. Kanagawa Prefect. Mus. Nat. Hist., No.13, pp. 43-60, 2008 (in Japanese with English abstract).
-  M. Nagai and M. Takahashi, “Geology and eruptive history of Hakone volcano, central Japan,” Res. Rep. Kanagawa Prefect. Mus. Nat. Hist., No.13, pp. 25-42, 2008 (in Japanese with English abstract).
-  T. Seno, S. Stein, and A. E. Gripp, “A model for the motion of the Philippine Sea Plate consistent with NUVEL-1 and geological data,” J. Geophys. Res. Solid Earth, Vol.98, Issue B10, pp. 17941-17948, 1993.
-  H. Kuno, “Dike swarm in Hakone volcano,” Bull. Volcanol., Vol.27, pp. 53-59, 1964.
-  R. Doke, M. Harada, K. Mannen, K. Itadera, and J. Takenaka, “InSAR analysis for detecting the route of hydrothermal fluid to the surface during the 2015 phreatic eruption of Hakone Volcano, Japan,” Earth, Planets and Space, Vol.70, Article No.63, 2018.
-  R. Honda, Y. Yukutake, Y. Morita, S. Sakai, K. Itadera, and K. Kokubo, “Precursory tilt changes associated with a phreatic eruption of the Hakone volcano and the corresponding source model,” Earth, Planets and Space, Vol.70, Article No.117, 2018.
-  R. Honda, Y. Yukutake, A. Yoshida, M. Harada, K. Miyaoka, and M. Satomura, “Stress-induced spatiotemporal variations in anisotropic structures beneath Hakone volcano, Japan, detected by S wave splitting: A tool for volcanic activity monitoring,” J. Geophys. Res. Solid Earth, Vol.119, Issue 9, pp. 7043-7057, 2014.
-  Y. Yukutake, T. Tanada, R. Honda, M. Harada, H. Ito, and A. Yoshida, “Fine fracture structures in the geothermal region of Hakone volcano, revealed by well-resolved earthquake hypocenters and focal mechanisms,” Tectonophysics, Vol.489, Issues 1-4, pp. 104-118, 2010.
-  Y. Yukutake, H. Ito, R. Honda, M. Harada, T. Tanada, and A. Yoshida, “Fluid-induced swarm earthquake sequence revealed by precisely determined hypocenters and focal mechanisms in the 2009 activity at Hakone volcano, Japan,” J. Geophys. Res. Solid Earth, Vol.116, Issue B4, Article No.B04308, 2011.
-  Y. Yukutake, R. Honda, Y. Abe, and S. Sakai, “Installation of temporary seismic stations in 2016,” Bull. Hot Springs Res. Inst. Kanagawa Prefect., Vol.48, pp. 33-36, 2016 (in Japanese).
-  J. A. Hudson, “Wave speeds and attenuation of elastic waves in material containing cracks,” Geophys. J. Roy. Astr. Soc., Vol.64, pp. 133-150, 1981.
-  X. R. Shih and R. P. Meyer, “Observation of shear wave splitting from natural events: South moat of Long Valley Caldera, California, June 29 to August 12, 1982,” J. Geophys. Res. Solid Earth, Vol.95, Issue B7, pp. 11179-11195, 1990.
-  B. Kuo, C. Chen, and T. Shin, “Split S waveforms observed in northern Taiwan: Implications for crustal anisotropy,” Geophys. Res. Lett., Vol.21, Issue 14, pp. 1491-1494, 1994.
-  R. Honda, Y. Yukutake, Y. Abe, and S. Sakai, “Azimuth verification of temporary seismic observation sites in and around Hakone volcano,” Bull. Hot Springs Res. Inst. Kanagawa Prefect., Vol.52, pp. 69-77, 2020 (in Japanese).
-  M. Kano, H. Nagao, S. Sakai, S. Nakagawa, S. Mizusako, M. Hori, N. Hirata, K. Shiomi, and R. Honda, “Azimuth verification of the MeSO-net Seismographs,” ZISIN (J. Seismol. Soc. Jpn. 2nd ser.), Vol.68, Issue 2, pp. 31-44, 2015 (in Japanese).
-  J. C. Bezdek, “Pattern Recognition with Fuzzy Objective Function Algorithms,” Plenum Press, 1981.
-  T. J. Ross, “Fuzzy logic with engineering applications,” 3rd Edition, John Wiley & Sons, Ltd., 2010.
-  J. C. Bezdek, “Numerical taxonomy with fuzzy sets,” J. Math. Biol., Vol.1, No.1, pp. 57-71, 1974.
-  K. Mannen, “Hakone caldera: Structure, mode of formation, and role in present-day volcanism,” Res. Rep. Kanagawa Prefect. Mus. Nat. Hist., No.13, pp. 61-76, 2008 (in Japanese with English abstract).
-  S. Kaneshima, “Origin of crustal anisotropy: Shear wave splitting studies in Japan,” J. Geophys. Res. Solid Earth, Vol.95, Issue B7, pp. 11121-11133, 1990.
-  Y. Nihara, K. Tadokoro, Y. Yukutake, R. Honda, and H. Ito, “Spatial distribution of crack structure in the focal area of a volcanic earthquake swarm at the Hakone volcano, Japan,” Earth, Planet and Space, Vol.65, pp. 51-55, 2013.
-  R. Doke, R. Honda, M. Harada, K. Miyaoka, T. Kato, and M. Satomura, “Deformation of the seismogenic zone in the northern part of the Izu Peninsula, Japan, inferred from GNSS observations,” Y. Dilek, Y. Ogawa, and Y. Okubo (Eds.), “Characterization of Modern and Historical Seismic–Tsunamic Events, and Their Global–Societal Impacts (Geological Society, London, Special Publications, Vol.501),” pp. 111-129, Geological Society of London, doi: 10.1144/SP501-2019-104, 2020.
-  S. Kaneko, “Deformation of Hakone Volcano South-West of Tokyo, Japan,” J. Geol. Soc. Japan, Vol.76, No.5, pp. 247-258, 1970.
-  Y. Daita, T. Tanada, T. Tanbo, H. Ito, M. Harada, and K. Mannen, “Temporal change of the pressure source estimated by tilt records during the 2001 Hakone swarm activity,” Bull. Volcano Soc. Jpn., Vol.54, Issue 5, pp. 223-234, 2009 (in Japanese).
-  Y. Yukutake, Y. Abe, R. Honda, and S. Sakai, “Magma reservoir and magmatic feeding system beneath Hakone volcano, central Japan, revealed by highly resolved velocity structure,” J. Geophys. Res. Solid Earth, Vol.126, Issue 4, Article No.e2020JB021236, 2021.
This article is published under a Creative Commons Attribution-NoDerivatives 4.0 Internationa License.