Japan (JPN)

Authors:

H. Fujiwara, N. Morikawa, S. Kawai, S. Aoi, S. Senna, T. Maeda, H. Azuma, K. X. Hao, A. Iwaki, K. Wakamatsu, M. Imoto, N. Hasegawa, T. Okumura, T. Hayakawa, M. Takahashi

Summary

The Global Hazard Mosaic coverage of Japan is based on the 2014 seismic hazard model issued by the Headquarters for Earthquake Research Promotion (HERP). The model is described by Fujiwara et al. (2009) and Fujiwara et al. (2015). The model has been translated from its original format into the OpenQuake (OQ) engine within a collaboration between the National Research Institute for Earth Science and Disaster Resilience (NIED), Japan, and GEM.

Information about the OQ model versions and input files can be found on the Results and Dissemination page.

Interactive Viewer

The viewer below depicts the seismic sources and hazard results in terms of PGA for a return period of 475 years. Click on the menu in the upper right corner to select the layer.

viewer_legend

Tectonic overview

Japan is located on the upper plates of several subduction zones, where oceanic plates of the western Pacific system subduct under crust of eastern Asia (primarily the Amur plate). At the latitude of central Honshu and farther north, the Pacific plate suducts under Japan at the Japan and Kuril trenches, which are continuous along strike. South of this latitude, the Pacific plate subducts under the Philippine Sea plate along the Izu-Bonin-Marianas trench, while the Philippine Sea plate subducts under Japanese crust in the Nankai Trough and, farther south, the Ryukyu Trench, which continues south to Taiwan (e.g., Loveless and Meade, 2010). Suduction of the Philippine Sea Plate under southern Japan is oblique, with a large right-lateral component, which is expressed in the right-lateral Median Tectonic Line dextral fault system through Shikoku and Kyushu. Stepovers in this system as well as additional slip partitioning and other second-order tectonic complexities result in distributed reverse, normal and strike-slip faults throughout the islands, which generate shallow, moderate-magnitude earthquakes that pose substantial hazard and risk for local populations.

Basic Datasets

See Fujiwara et al. (2009) and Fujiwara et al. (2015) for a description of the datasets used for developing the hazard model.

Hazard Model

Seismic Source Characterisation

The seismic source characterisation (SSC) consists of various seismic source typologies to describe earthquake occurrence in different tectonic settings. They are classified according to three categories: the first includes subduction-zone earthquakes modelled on well-constrained faults; the second includes subduction interplate and intraplate earthquakes which lack well-defined source faults (i.e. modelled in the background); and the third comprises all other shallow crustal earthquakes sources occurring onshore, offshore, on well-constrained faults, and in the background.

The SSM for Japan considers the time-dependent earthquake occurrence on some crustal and subduction faults. For mega-subduction interface ruptures, a number of possible mutually exclusive and collectively exhaustive sets of ruptures are defined in a finite period of time and each assigned a corresponding probability of occurrence.

The OQ implementation uses three OQ source typologies. The background (gridded) seismicity is implemented as collections of Point Sources. Crustal and Subduction faults with a time-independent model are modelled using Characteristic Fault Sources with planar surfaces, and those with a time-dependent behavior are modeled as Nonparametric Sources. The OQ sources are depicted in the interactive viewer.

Ground Motion Characterisation

The table below shows the ground motion characterisation (GMC), which is comprised of a set of ground motion prediction equations (GMPEs).

The origial seismic hazard maps for Japan provide estimates of JMA seismic intensity and peak ground velocity. To compute hazard in terms of peak ground acceleration (PGA), an updated to the GMPE Si and Midorikawa (1999) GMPE was added to OQ and used for the hazard computation.

The GMM for the 2014 Japan model distinguishes between five main tectonic regions: Active Shallow Crust, Subduction Interface, Subduction Interface - North East Correction, Subduction IntraSlab - North East Correction,and Subduction IntraSlab - South West Correction.

Active Shallow Crust Weight
SiMidorikawa1999Asc 1.0
Subduction Interface Weight
SiMidorikawa1999SInter 1.0
Subduction Interface - North East Correction Weight
SiMidorikawa1999SInterNorthEastCorrection 1.0
Subduction IntraSlab - North East Correction Weight
SiMidorikawa1999SSlabNorthEastCorrection 1.0
Subduction IntraSlab - South West Correction Weight
SiMidorikawa1999SSlabSouthWestCorrection 1.0

Results

Hazard curves were computed with the OQ engine for peak ground acceleration (PGA) and spectral acceleration (SA) at 0.2s, 0.5s, 1.0s, and 2s. The computation was performed on a grid of 13879 sites (spaced at approximately 10 km) with reference soil conditions with shear wave velocity in the upper 30 meters (Vs30) of 760-800 m/s.

The hazard map for PGA corresponding to a 10% probability of exceedance in 50 years (475 year return period), can be seen using the interactive viewer. For a more comprehensive set of hazard and risk results, please see the GEM Visualization Tools.

References

Fujiwara, H., Kawai, S., Aoi, S., Morikawa, N., Senna, S., Kudo, N., Ooi, M., Hao, K. X., Wakamatsu, K., Ishikawa, Y., Okumura, T., Ishii, T., Matsushima, S., Hayakawa, Y., Toyama, N. and Narita, A. (2009). Technical reports on national seismic hazard maps for Japan, Technical Note of the National Research Institute for Earth Science and Disaster Resilience, No. 336, 512 pp.

Fujiwara, H., Morikawa, N., Kawai, S., Aoi, S., Senna, S., Maeda, T., Azuma, H., Hao, K. X., Iwaki, A., Wakamatsu, K., Imoto, M., Hasegawa, N., Okumura, T., Hayakawa, T., Takahashi, M. (2015). Improved seismic hazard assessment after the 2011 great East Japan earthquake,” Technical Note of the National Research Institute for Earth Science and Disaster Resilience, No. 399