Science of Slow Earthquakes

Science of Slow Earthquakes - Toward a unified understanding of all earthquake events from low-speed deformation to high-speed slip

Project OverviewGroup A02: Geodetic Observations (Area number: JP16H06474)
Study on Physical Mechanisms of Slow Earthquakes based on Geodetic ObservationsLeader: Hitoshi HIROSE, Research Center for Urban Safety and Security, Kobe University

  1. Admin, Int
  2. A01
  3. A02
  4. B01
  5. B02
  6. C01
  7. C02

Purpose of the Research Project

Various types of slow earthquakes have been found in a number of plate boundaries, particularly in subduction zones. The world's most diversified activities of slow earthquakes have been discovered along the Nankai Trough and Ryukyu Trench in western Japan. However, regional factors controlling the difference of those activities, interactions among regions and relationship among different types of slow earthquakes have not been clearly explained yet. Group A02 conducts an observational research to precisely detect activities of slow slip events (SSEs), the largest type of slow earthquakes that are thought to control the macroscopic patterns of slow earthquake activities and interplate slip modes, in some areas in western Japan where SSE activity is high by using multi geodetic techniques such as GNSS, tiltmeters, strainmeters, and gravimeters in order to address the regional characteristics of the interplate slip property, factors controlling them, interactions among activities in neighboring regions and relationship between SSEs occurrence and crustal fluid. Further, we aim to redefine the earthquake phenomena through understanding slow earthquakes by integrating findings from other research groups, such as observational results, laboratory experiments, and numerical models.

Figure 1. Target areas and locations of slow earthquakes.

Details of the Research

Based on geodetic observation techniques, we proceed following three themes integrally.

  • A) Determination of the slip areas of SSEs and the understanding of the interactions among SSEs
    We deploy new continuous GNSS stations to observe precise SSE slip processes around the Bungo Channel and associated SSE activity changes in neighboring areas. Integrating these data with those from existing observation networks of GNSS, tiltmeters and strainmeters, we determine the slip extents and slip velocities of each SSE and gain knowledge on friction characteristics in the SSE source areas and reveal the interactions between neighboring SSEs
  • B) Examination of environmental factors responsible for the occurrence mode of SSEs
    Setting two areas where isolated SSEs occur once or twice a year: 1) the area around the Okinawa Island where SSEs are located in a shallow area on the plate interface; 2) the Yaeyama Islands where SSEs are located in a deep area on the plate interface; as model areas, we conduct continuous GNSS observation in island areas not covered by GEONET (nationwide GNSS observation network operated by Geospatial Authority of Japan). We study the environmental factors controlling slip characteristics on the plate interface in those areas by clarifying the mode of SSE activity, such as recurrence intervals, slip duration, depth ranges, and so on.
  • C) Detection of crustal fluid migration associated with SSEs
    We try to detect gravity changes associated with the occurrence and progress of SSEs using portable and continuous gravimeters in order to determine the effect of crustal fluids existing in SSE areas on the generation of SSEs. By this observation with high temporal resolution, we improve the identification accuracy of crustal fluid behavior at depth.


Project Leader
  • HIROSE, HitoshiResearch Center for Urban Safety and Security, Kobe University
  • MIYAZAKI, ShinichiGraduate School of Science, Kyoto University
  • MATSUSHIMA, TakeshiFaculty of Science, Kyushu University
  • TABEI, TakaoResearch and Education Faculty, Natural Sciences Cluster, Sciences Unit, Kochi University
  • YAMAZAKI, KenichiDisaster Prevention Research Institute, Kyoto University
  • TAKAGI, RyotaGraduate School of Science, Tohoku University
  • TANAKA, YoshiyukiDepartment of Earth and Planetary Science, The University of Tokyo
  • KIMURA, TakeshiEarthquake and Tsunami Research Division, National Research Institute for Earth Science and Disaster Resilience
  • ITABA, SatoshiResearch Institute of Earthquake and Volcano Geology, National Institute of Advanced Industrial Science and Technology
Research Collaborators
  • NISHIMURA, TakuyaDisaster Prevention Research Institute, Kyoto University
  • OHTA, YusakuGraduate School of Science, Tohoku University
  • YARAI, HiroshiGeography and Crustal Dynamics Research Center, Geospatial Information Authority of Japan
  • IMANISHI, YuichiEarthquake Research Institute, The University of Tokyo
  • NAWA, KazunariGeological Survey of Japan, National Institute of Advanced Industrial Science and Technology
  • OGAWA, TsutomuEarthquake Research Institute, The University of Tokyo
  • KANO, MasayukiGraduate School of Science, Tohoku University
  • NAKATA, RyokoGraduate School of Science, Tohoku University
  • OHZONO, MakoEarthquake Research Institute, The University of Tokyo/Institute of Seismology and Volcanology, Graduate School of Science, Hokkaido University
  • IINUMA, TakeshiResearch and Development Center for Earthquake and Tsunami Forecasting, Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology
  • KINOSHITA, YoheiFaculty of Engineering, University of Tsukuba
  • ITOH, YujiEarthquake Research Institute, The University of Tokyo

Group Research Subthemes

Co-investigater's Subjects
  • Hirose, Hitoshi, MIYAZAKI, Shinichi, MATSUSHIMA, Takeshi, TABEI, Takeo, YAMAZAKI, Kenichi, NISHIMURA, Takuya Continuous GNSS observation for crustal deformation due to slow slip events in southwest Japan
  • TAKAGI Ryota Slow slip event inferred from GNSS data analysis and interaction with tremor activity
  • TANAKA, Yoshiyuki, IMANISHI, Yuichi, NAWA, Kazunari, OGAWA, Tsutomu Precise gravity and electromagnetic observations in slow slip areas
  • KIMURA, Takeshi To be updated
  • ITABA, Satoshi To be updated