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 A01: Seismic Observations (Area number: JP16H06473)
Study on the Mechanisms Involved in the Occurrence of Slow Earthquakes Based on Temporal Inland and Offshore ObservationsLeader: Kazushige OBARA, Earthquake Research Institute, The University of Tokyo

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

Purpose of the Research Project

Slow earthquakes are the phenomena characterized by slow fault ruptures. They have been discovered along subducting oceanic plates in Japan and the Circum-Pan-Pacific since around the end of the 20th century. Slow earthquakes are considered to have some sort of interactions with occurrence of huge earthquakes since slow earthquakes occur in adjacent areas of huge earthquake seismogenic zones. However, the physical process of the phenomena has not been explained well yet. Group A01 aims at clarifying spatiotemporal evolution of slow earthquakes, interaction of neighboring slow earthquakes, and triggering phenomena caused by tides or teleseismic waves based on temporal inland and offshore observations. Our ultimate goal is to achieve unified understanding of all the earthquakes such as low-speed deformation and high-speed slips, in other words, the significant viewpoint which is lacked in existing earthquake studies, through multidisciplinary understanding of slow earthquakes by integrating geodetic occurrence styles revealed by other research groups, geophysical/geological scientific environment and geoscientific/physical models associated with the phenomena.

Figure 1. Distribution of various slow earthquakes occurring in the Nankai Trough subduction zone. Migration is observed in deep slow earthquakes (ETS, long-term SSEs) and shallow slow earthquakes. Long-term SSEs are characterized by causing other slow earthquakes activities in surrounding areas. Similar mutual interactions are possibly expected between slow earthquakes and huge earthquakes.

Details of the Research

Based on permanent earthquake observations and temporal inland and offshore observations, research is targeted at slow earthquakes as follows.

  • A) Shallow Slow Earthquakes
    We intend to geodetically detect shallow SSEs expected to exist in the area of the western Nankai Trough and Ryukyu Islands, estimate the spatial distribution of the slips and clarify detailed spatiotemporal evolution of shallow tremor/very-low frequency earthquakes and behavior of tidal response for scaling and evaluation of correlation of such phenomena.
  • B) Deep Slow Earthquakes
    We aim at clarifying behavior of tidal response and phenomena caused by teleseismic surface waves as well as extract detailed spatiotemporal evolution of deep low frequency tremors including very high-speed migration and very-low frequency earthquakes in western Shikoku, where the activities are most noticeable in southwest Japan. After that we will intend to reveal applicability of the scaling rules in small events of deep very-low frequency earthquakes and determine mutual interaction of them.
  • C) Repeating Earthquakes
    We will work on evaluating slow slips by analyzing repeating earthquakes from the Nankai Trough to the Ryukyu Islands for clarifying spatiotemporal variation and mutual interaction of surrounding shallow slow earthquakes and usual earthquakes
    We intend to determine the mutual interaction of shallow/deep slow earthquakes described in A) and B) as well as the similarities/differences in behavior of them described in A), B) and C).

Then we will quantitively evaluate the influences of long-term slow slip events utilizing fault parameters measured by Group A02 (Study on physical mechanisms of slow earthquakes based on geodetic observations)


Project Leader
  • OBARA, KazushigeEarthquake Research Institute, The University of Tokyo
  • SHINOHARA, MasanaoEarthquake Research Institute, The University of Tokyo
  • YAMASHITA, YusukeDisaster Prevention Research Institute, Kyoto University
  • ASANO, YouichiEarthquake and Tsunami Research Division, National Research Institute for Earth Science and Disaster Resilience
  • NAKAMURA, MamoruFaculty of Science, University of the Ryukyus
  • TANAKA, SachikoEarthquake and Tsunami Research Division, National Research Institute for Earth Science and Disaster Resilience
  • MIYAZAWA, MasatoshiDisaster Prevention Research Institute, Kyoto University
  • UCHIDA, NaokiGraduate School of Science, Tohoku University
Research Collaborators
  • SUGIOKA, HirokoGraduate School of Science, Kobe University
  • TSURUOKA, HiroshiEarthquake Research Institute, The University of Tokyo
  • KATO, AitaroEarthquake Research Institute, The University of Tokyo
  • TAKEO, AkikoEarthquake Research Institute, The University of Tokyo
  • SUDA, NaokiGraduate School of Science, Hiroshima University
  • OKUBO, MakotoResearch and Education Faculty, Natural Sciences Cluster, Sciences Unit, Kochi University
  • KURASHIMO, EijiEarthquake Research Institute, The University of Tokyo
  • ISHISE, MotokoEarthquake Research Institute, The University of Tokyo
  • KANO, MasayukiGraduate School of Science, Tohoku University
  • TANAKA, YusakuGraduate School of Environmental Studies, Nagoya University
  • FUJITA, KoheiEarthquake Research Institute, The University of Tokyo

Group Research Subthemes

Co-investigater's Subjects
  • SHINOHARA, Masanao, YAMASHITA, Yusuke, SUGIOKA, Hiroko Study on the Activity of Shallow Slow Earthquakes Based on Ocean Bottom Broad-band Seismic and Geodetic Observations
  • ASANO, Youichi To be decided
  • NAKAMURA, Mamoru Spatial and temporal variation in tidal response of very low frequency earthquakes in the Ryukyu Trench
  • TANAKA, Sachiko Spatial and temporal changes in tidal modulation of nonvolcanic tremor and very low frequency earthquakes
  • MIYAZAWA, Masatoshi Detection of temporal changes of frictional parameters on the plate interface by using dynamic triggering of tremor
  • UCHIDA, Naoki Interaction between various slip events on the plate boundary
  • OBARA, Kazushige, TAKEO, Akiko Study on the activity of deep slow earthquakes from inland broadband seismic observation
  • OBARA, Kazushige, KATO, Aitaro, KURASHIMO Eiji Tremor scope through very dense seismic arrays