19 Octobre 2012
October 19, 2012
The Seismological Society of Japan (SSJ) has drafted an action plan aimed at reforming itself. In the draft, the group admits that it is extremely difficult at the current stage to accurately predict earthquakes and says it will not use the phrase, "earthquake prediction," to mean stochastic forecasts.
However, just changing the phrase is far from sufficient. The society should continue to discuss specific measures that the government should take to prevent damage from earthquakes and how to forecast tremors.
Earthquake prediction has been defined as grasping when and where earthquakes will occur and how large and powerful they are in advance.
Such predictions are regarded as highly accurate information based on which the government issues quake warnings. The Act on Special Measures concerning Countermeasures against Large-scale Earthquakes, which came into force in 1978 in anticipation of a Tokai earthquake expected to hit central Japan, is based on this definition.
However, the Great Hanshin Earthquake that devastated Kobe and surrounding areas in 1995 has proven that predicting earthquakes is impossible at the present time. Nevertheless, the phrase, "earthquake prediction," has been widely used at universities and government bodies. The nation as a whole should reconsider the use of the phrase.
On the other hand, earthquake forecasting shows the chance that an earthquake with a certain scale will occur in a specific area within certain years. Since the Great Hanshin Earthquake, the government's Earthquake Research Committee has worked on long-term forecasts for powerful earthquakes in Japan.
However, the March 2011 Great East Japan Earthquake has shown that such long-term forecasting is also unreliable. The committee had forecast the chances of earthquakes hitting several areas off the Boso Peninsula in Chiba Prefecture to the Sanriku area in the Tohoku region within 30 years and the scales of the tremors. However, it was unable to forecast the magnitude-9 Great East Japan Earthquake, which occurred as a result of multiple plates moving together.
As such, an important lesson learned from the March 11, 2011 earthquake is that predicting earthquakes immediately before they occur and long-term forecasting are unreliable. It is theoretically difficult to forecast massive earthquakes because such disasters do not occur frequently and experts have not clarified the mechanism of such massive temblors occurring.
The SSJ should not send the wrong message that long-term earthquake forecasting is reliable while it is impossible to accurately predict earthquakes shortly before they hit by overemphasizing that it will stop using the phrase, "earthquake prediction." The SSJ should rather place priority on fulfilling its role of correctly notifying the public of the current seismology situation as it pledges in the draft of its action plan.
Limits on seismology should be kept in mind in surveying active faults near nuclear power plants. The government's Nuclear Regulation Authority will conduct an on-the-spot inspection on the Oi Nuclear Power Plant operated by Kansai Electric Power Co., and will consider whether it is necessary to conduct such an inspection on active faults near six other nuclear-related facilities. Regardless of the outcome of such inspections, it is indispensable to take into consideration the risks of massive earthquakes hitting these facilities.