Quake lessons after 13 years

Thirteen years have passed since the Great Hanshin Earthquake on Jan. 17, 1995. The magnitude 7.3 quake occurred in the Inland Sea and caused 6,434 deaths. Since then, other deadly quakes and quake studies have shown that Japan needs to improve its earthquake preparedness and to strengthen quake-related observation and research.

According to a worst-case scenario predicted by a panel of the Central Disaster Prevention Council, more than 10,000 people would die in each major earthquake in five of eight fault zones studied in the Kinki region. A major quake in the Uemachi fault zone in Osaka Prefecture would kill up to 42,000 people, followed by 19,000 in a major quake in the Ikoma fault zone in the Osaka-Kyoto-Nara border area.

While quake predictions are impossible, enhanced observation and research can improve warnings that tell how many seconds it will take tremors from a major earthquake to reach specific areas. They can also make a positive contribution to studies aimed at determining the patterns of future quake vibrations and improving the designs of buildings and other structures.

Creating a better network of strong-motion seismographs to record strong quake vibrations will be especially important. Depending on the types of quakes — whether they occur directly below populated areas or as a result of tectonic plate collisions — the periods of vibrations differ. Structural designs must be able to cope with these differences.

In the Great Hanshin Earthquake, which occurred close to populated areas such as Kobe, the periods of strong tremors were one to two seconds. In the case of interplate earthquakes, the corresponding periods are believed to be longer. High-rise structures can vibrate in resonance with long-period tremors, with the vibrations of the structures growing stronger. The government should realize that a better network of strong-motion seismographs would help reduce damage in major quakes.