PSHA input model documentation for Japan(JPN)GEM Hazard TeamVersion history
Table 1 summarises version history for the JPN input model, named according to the versioning system described here, and indicating which version was used in each of the global
maps produced since 2018. Refer to the GEM Products Page for information on whichmodel versions are available for various use cases. The changelog describes the changes
between consecutive versions and are additive for all versions with the same model year.

Table 1 – Version history for the JPN input model.

Versionv2014.0.0

2018.1 2019.1 2022.1 2023.1 Changelog
XXXv2021.0.0

First version of the model implemented in OpenQuake.
The 2021 version of the nationalmodel by NIED. Translated into OQby GEM.

XThe following text describes v2021.0.0.

2Authors: H. Fujiwara, N. Morikawa, T. Maeda, A. Iwaki, S. Senna, S. Kawai, H. Azuma, X. Hao,
M. Imoto, K. Wakamatsu, J. Miyakoshi, T. Morii, N. Shimazu, M. Takahashi, M. Akatsuka

1Summary

The Global Hazard Mosaic coverage of Japan is based on the 2021 seismic hazard modelissued by the Headquarters for Earthquake Research Promotion (HERP). The model is described by Fujiwara et al. (2009), Fujiwara et al. (2015), and Fujiwara et al. (2023). 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.

2Tectonic 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 atthe Japan and Kuril trenches, which are continuous along strike. South of this latitude, thePaciﬁc 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, moderatemagnitude earthquakes that pose substantial hazard and risk for local populations.

3

Basic Datasets

See Fujiwara et al. (2009), Fujiwara et al. (2015), and Fujiwara et al. (2023) for a descriptionof the datasets used for developing the hazard model.

4Hazard Model

4.1Seismic Source Characterisation

The seismic source characterisation (SSC) consists of various seismic source typologies todescribe earthquake occurrence in different tectonic settings. They are classiﬁed according to three categories: the ﬁrst includes subduction-zone earthquakes modelled on wellconstrained faults; the second includes subduction interplate and intraplate earthquakes
3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 wellconstrained faults, and in the background.
The SSM for Japan considers the time-dependent earthquake occurrence on some crustaland 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 oftime 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 atime-independent model are modelled using Characteristic Fault Sources with planar surfaces, and those with a time-dependent behavior are modeled as Nonparametric Sources.

4.2Ground Motion Characterisation

The table below shows the ground motion characterisation (GMC), which is comprised ofa set of ground motion prediction equations (GMPEs).
The origial seismic hazard maps for Japan provide estimates of JMA seismic intensity andpeak ground velocity. To compute hazard in terms of peak ground acceleration (PGA), an
update to the GMPE Si and Midorikawa (1999) GMPE was added to OQ and used for thehazard computation. This was used to calculate PGA values on rock. A second logic tree
(Table 3) was used for other intensity measure types (IMTs) and for all results computedfor spatially varying vs30.
The GMM for the 2021 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
SiMidorikawa1999Asc
Subduction Interface
SiMidorikawa1999SInter
Subduction Interface - North East Correction
SiMidorikawa1999SInterNorthEastCorrection
Subduction IntraSlab - North East Correction
SiMidorikawa1999SSlabNorthEastCorrection
Subduction IntraSlab - South West Correction
SiMidorikawa1999SSlabSouthWestCorrection

Weight1.0
Weight1.0
Weight1.0
Weight1.0
Weight
1.0

Table 2 – GMPEs used in the Japan model for calculating PGA on rock.

Subduction Interface - South West Correction
AbrahamsonEtAl2015SInter
ParkerEtAl2020SInter
4

Weight0.5
0.25

ZhaoEtAl2016SInter
Subduction IntraSlab
AbrahamsonEtAl2015SSlab
ParkerEtAl2020SSlab
ZhaoEtAl2016SSlab
Subduction Interface - North East Correction
AbrahamsonEtAl2015SInter
ParkerEtAl2020SInter
ZhaoEtAl2016SInter
Subduction IntraSlab - South West Correction
AbrahamsonEtAl2015SSlab
ParkerEtAl2020SSlab
ZhaoEtAl2016SSlab
Subduction Interface
AbrahamsonEtAl2015SInter
ParkerEtAl2020SInter
ZhaoEtAl2016SInter
Active Shallow Crust
ChiouYoungs2014
BooreEtAl2014
ZhaoEtAl2016Asc
Subduction IntraSlab - North East Correction
AbrahamsonEtAl2015SSlab
ParkerEtAl2020SSlab
ZhaoEtAl2016SSlab

0.25
Weight
0.5
0.25
0.25
Weight
0.5
0.25
0.25
Weight
0.5
0.25
0.25
Weight
0.5
0.25
0.25
Weight
0.35
0.35
0.3
Weight0.50.25
0.25

Table 3 – GMPEs used in the JPN model for calculating results on spatially varying vs30 and forintensity measure types other than PGA.

5Results

Hazard curves were computed with the OQ engine for the following:• Intensity measure types (IMTs): peak ground acceleration (PGA) and spectral acceleration (SA) at 0.2s, 0.3s, 0.6s, 1.0s, and 2s• reference site conditions with shear wave velocity in the upper 30 meters (Vs30) of760-800 m/s, as well as for Vs30 derived from a topography proxy (Allen and Wald,2009)
Hazard maps were generated for each reference site condition-IMT pair for 10% and 2%
probabilities of exceedance (POEs) in 50 yrs. Additionally, disaggregation by magnitude,
distance, and epsilon was computed for the following cities: Tokyo. The results were produced as csv ﬁles and bar plots for each of the following combinations:5• hazard levels for 10% and 2% POE in 50 yrs• PGA and SA at 0.2s, 0.3s, 0.6s, and 1.0s
• Vs30=800 m/s
All calculations used a ground motion sigma truncation of 5. Results were computed forsites with 6 km spacing
Visit the GEM Interactive Viewer to explore the Global Seismic Hazard Map values (PGA for
Vs30=800 m/s, 10% poe in 50 years). For a comprehensive set of hazard and risk results,
see the GEM Products Page.

6References

Allen, T. I., and Wald, D. J., 2009, On the use of high-resolution topographic data as a proxyfor seismic site conditions V s30, Bulletin of the Seismological Society of America, 99, no.
2A, 935-943
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. andNarita, 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
Fujiwara, H., Morikawa, N., Maeda, T., Iwaki, A., Senna, S., Kawai, S., Azuma, H., Hao, X.,Imoto, M., Wakamatsu, K., Miyakoshi, J., Morii, T., Shimazu, N., Takahashi, M. and Akatsuka, M. (2023). Improved seismic hazard assessment after the 2011 great East Japanearthquake (Part 2). Technical Note of the National Research Institute for Earth Scienceand Disaster Resilience, No. 489

6Last processed: Thursday 8th June, 2023 @ 18:18
www.globalquakemodel.org
If you have any questions please contact the GEM Foundation Hazard Team at: hazard@globalquakemodel.org

7