Review and Assessment of Earthquake Intensity Information

Abstract

The manner in which earthquake intensity information is obtained and applied in Japan is in a state of constant revision. Increasingly, however, issues and problems are also brought to the forefront. After the occurrence of recent earthquakes, including the Mid Niigata Prefecture Earthquakes in 2004 and the Northwestern Chiba Prefecture Earthquake, critical assessments regarding earthquake intensity information have been issued. The problem regarding earthquake intensity information is nothing new; however, this problem has attracted increased attention since it was pointed out that the delay in the issuance of earthquake intensity information about the Great Hanshin-Awaji Earthquake in 1995 caused a delay in the initial reaction to it. The reasons for this are that problems have become pronounced due to the increase of unmanned observation points and observation points that are not managed by the Meteorological Agency due to the transition of intensity observation from the sensation to the seismic intensity meter, and an increase in the focus on the rapidity of information release rather than earthquake intensity recording performance. However, as long as measurements are conducted by machine, problems must be expected. Therefore, based on lessons from the Great Hanshin-Awaji Earthquake, it was decided that newly received but unconfirmed information on earthquakes of an intensity greater than 5 lower would be announced; however, this standard is still not applied effectively. There may be a need to review the delivery of earthquake intensity information, currently delivered as reference information for the purpose of understanding seismic conditions, to prioritize its use as conclusive information reflecting accurate seismic conditions.