Miyazaki Quakes Raise Awareness Of Nanakai Trough

Japan Meteorological Agency Graphic Of Nankai Trough

The Central Disaster Prevention Council is urging reinforced countermeasures against a huge Nankai Trough earthquake in light of the recent activity along the trough in the last week.

Since Friday there have been a total of 7 earthquakes in the trough area near the Miyazaki coastline. The quakes have ranged in magnitude from 6.4 to 3.8.  Other quakes have occured since Tuesday in Kochi Prefecture on the island Shikoku, the bay of Hiroshima and in the Tokai bay off the coast of Southeast Aichi Prefecture.  These quakes ranged from 3 to 4.5.

Part of a review of disaster prevention steps based on the Act on Special Measures Concerning Countermeasures for Large-Scale Earthquakes has been underway since Saturday. 
 

The government is to review measures to send out disaster management information, which are in place based on the assumption that such a powerful earthquake is predictable. In the report, Shizuoka and Kochi prefectures, as well as the Chubu economic region centered in Nagoya, are selected as model areas, with discussion about specific disaster prevention measures. 

While there is no specific mention of reviewing the Act on Special Measures Concerning Countermeasures for Large-Scale Earthquakes itself, it states that disaster prevention steps should be reviewed on the grounds that "it is not possible to predict an earthquake with a high degree of certainty." 

In addition, there are four scenarios of a major earthquake occurring. These are: 1) a huge tremor occurring east of the hypocentral region of a major Nankai Trough earthquake; 2) a magnitude 7 earthquake occurring in the same hypocentral region; 3) observation of changes such as a decrease in the number of quakes -- as was the case before the Great East Japan Earthquake in 2011; 4) and observation of ominous "sliding plates" that would suggest a Tokai tremor is imminent. 

In the case of 1) and 2), the probability of additional quakes occurring becomes higher, therefore making it necessary to consider evacuating residents in advance and other measures. In addition, in the case of 3), "it is not possible to determine whether this will lead to a major tremor," and therefore it is judged that prior evacuation measures are not possible. 

On the other hand, in the case of 4), the prime minister is supposed to issue warning statements in accordance with the Act on Special Measures Concerning Countermeasures for Large-Scale Earthquakes -- asking residents to evacuate in advance as well as halting public transport services. 

However, it has been pointed out that it is not possible to judge the extent to which an earthquake occurring has become more likely. But administrative bodies need to be on alert, but at the same time it is difficult to ask residents to evacuate in advance.

Chief Cabinet Secretary Yoshihide Suga said yesterday, "We need to hurry ahead with these disaster prevention measures." In particular, disaster countermeasures in cases 1), 2) and 4) need to be revised. 

With regard to local authorities that have been selected as model districts in the report, aspects such as the kinds of residents who should be evacuated in advance, the length of the evacuation, and evacuation areas will be discussed. Based on this, local authorities will draw up guidelines relating to disaster prevention in their respective areas. 

Since the 6.4 quake in Miyazaki on Friday morning the latest aftershock earthquake occurred today at 7:20am in Hyuga Bay off the coast of Nobeoka, Miyazaki Prefecture with a magnitude of 3.7.  There were no reports of damage or injury.