About J-RISQ earthquake report

J-RISQ earthquake report is a compact summary of information concerning an earthquake disaster based on data estimated by the J-RISQ system immediately after an earthquake. The report contains the spatial and frequency distributions of seismic intensity ("I_s") for cities, population exposed to certain level of I_s, and historical damaging earthquake data as well as seismic hazard information for the region.

Specific Disclaimer

• The observed I_s shown in a J-RISQ earthquake report is not always the same value as the information reported by the JMA (Japan Meteorological Agency).
• The estimated I_s is sometimes larger than the maximum observed I_s due to the site amplification factors.
• The population data is based on the past survey.
• Click here for details.
• It may take time to update a municipal merger, and therefore, the old names of cities, towns, and villages may be shown.

About Released reports

How to Use a J-RISQ Earthquake Report

Access with a Laptop or Desktop

• Access to J-RISQ Report web site.
• 1. Click on the date on the calendar.
• 2. The reports of the day are displayed under the calendar. Click on the report from the list.
• 3. The J-RISQ earthquake report is displayed on the right side.
• 4. Click on PDF Download button to get the PDF file.
• 5. Click on KML Download button to get the KML file.
• 6. Click on Auto Update button to turn on/off the automatic updates.
  * If you select a date or select an earthquake, automatic updates turn off.
• 7. Announcement field is displayed when we have notification.

Access with a Smartphone

Accessing web site with a smartphone, the mobile website is shown automatically.

Example of Report

Information in a J-RISQ Earthquake Report

1. Versions

The J-RISQ system is triggered to make a first version of the report when the system receives the I_s data of 2.5 or greater from more than 2 stations. The system revises the report versions if the I_s data received after making the previous version meet the above-mentioned criteria. Usually, the first version is issued around 1 minute after receiving the first I_s data and 3-5 versions are made after that. The system starts to make a final version using all the available data 10 minutes after triggered.

2. Hypocenter Information

A J-RISQ earthquake report shows the hypocenter information provided by the JMA that seems to be related to the shakings or I_s data set. "Undetermined" is displayed if the J-RISQ system does not receive the hypocenter information when making the report.

3. 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 in the following methods.
• Reports other than final version
• Delaunay triangular interpolation algorithm (Shewchuk, 1996)
• Final version report
• 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).

4. 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.

5. 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.

6. 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.

7. Seismic Hazard Information of J-SHIS

Seismic hazard information is referenced from National Seismic Hazard Maps of Japan (2012 model 1) 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.