About J-RISQ past earthquake Report

J-RISQ past earthquake Report is analysis of earthquakes which cause seismic intensity (I_s) of 3 or above from May 1996 to March 2011.
See Information in a J-RISQ Earthquake Report for details on J-RISQ Real-time Report on and after April 2011.

1. Earthquake Information

• I_s data observed by K-NET or KiK-net
• I_s data observed by JMA (Japan Meteorological Agency) or local governments
• JMA seismic intensity data in the Seismological Bulletin of Japan by JMA
• Hypocenters
• Hypocenters in the Seismological Bulletin of Japan by JMA

2. I_s Distribution Map

Draw Spatial distribution of I_s estimated from the observed data.

Calculation Process

1. Estimate PGV (Peak Ground Velocity) by using the following relationship between I_s and PGV (Fujimoto and Midrorikawa, 2005),
   ... (1).
2. Estimate PBV (Peak Basement Velocity) by dividing PGV by site amplification factor.
3. Estimate spatial distribution of PBV in 250-m meshes by IDW (Inverse distance weighting) interpolation algorithm.
4. Multiply PBV by the amplification factor to derive the PGV distribution and then convert to the I_s distribution using the relationship (1).

3. Table of Estimated I_s for Major Cities

The table lists the maximum observed I_s and frequency distribution (histogram) of the estimated Is for major cities considering the maximum observed value and populations.

Estimation Process of I_s Frequency Distribution

1. Calculate a number of 250-m meshes for each municipality and each I_s scale from the estimated I_s distribution data. If the meshes are across the plural municipalities, the number of meshes is allocated to municipalities considering the ratio of the areas.
2. Divide the number of 250-m meshes for each I_s scale by the total number of the meshes in the municipality and round the number by 5% scale.

4. Maps and Table of I_s Exposed Populations for Municipalities and Prefectures

1. Pick up the 250-m mesh which experiences a threshold I_s.
2. Count the exposed population for the I_s level in the meshes.
3. Calculate a sum of the I_s exposed population for each municipality and prefecture. If the meshes are across the plural municipalities, the populations are allocated to municipalities considering the ratio of the areas.

5. Major Historical Damaging Earthquakes in This Region

Historical damaging earthquakes around the epicenter are referenced from the Chronological Scientific Tables, “Rika Nenpyo Web Edition”, written by National Astronomical Observatory of Japan, published by MARUZEN.

6. Seismic Hazard Information of J-SHIS

Seismic hazard information is referenced from National Seismic Hazard Maps of Japan (2016 version) provided by J-SHIS. J-SHIS is a Web service by NIED, to help prevent and prepare for earthquake disaster by providing a public portal for seismic hazard information across Japan.

• Probabilistic Seismic Hazard Map of I_s for a 2% probability of exceedance in 50 years (Return period is 2,500 years)
  represents relatively high-frequency seismic hazard.
• Averaged Hazard Map of I_s with a return period of 50,000 years
  represents relatively low-frequency seismic hazard.

Acknowledgments

This work was partially supported by the Council for Science, Technology and Innovation (CSTI) through the Cross-ministerial Strategic Innovation Promotion Program (SIP), titled "Enhancement of social resiliency against natural disasters" (Funding agency: JST).

We are grateful to the JMA for providing the I_s data observed at the JMA and local government stations and hypocenter information.