Measures to cope with earthquakes

Similarly, to scientifically advance earthquake-resistant design, we conduct analyses of what will happen when assumed earthquake motion is applied, and verify whether the results meet the objectives. However, it is not possible to analyze everything. And damage occurs in places that cannot be analyzed. We must humbly accept what did and did not happen in the actual earthquake, sort out the causal relationships with earthquake motion, and place importance on the facts to move forward with earthquake-resistant design as empirical engineering.

The Tohoku Pacific Ocean Earthquake caused a maximum seismic intensity of 5+ in central Tokyo. The term "seismic intensity 5+" was coined after the Great Hanshin-Awaji Earthquake, when the previous seismic intensity of 5 was divided into "5-weak" and "5+". Niigata City experienced a seismic intensity of 5 in the 1964 Niigata earthquake, and Sendai City experienced a seismic intensity of 5 in the 1976 Miyagi Prefecture offshore earthquake, so central Tokyo experienced seismic motion comparable to these. I was on the 8th floor of a 9-story building and was amazed by the shaking, which was undoubtedly of intensity 5+. The last time Tokyo was hit by a major earthquake was the Great Kanto Earthquake of 1923, 88 years ago, and this was the first major earthquake of intensity 5+ that Tokyo has experienced since then. It may be that the periodic components that cause damage to buildings were weak, but this earthquake is likely to be positioned as the standard for a major earthquake in Tokyo.

From this point of view, when we look at the relationship with earthquake-resistant design issues in Tokyo, the first issue is the problem of long-period earthquake motion. The shaking experienced this time in the super high-rise buildings in central Tokyo is exactly the long-period earthquake motion that has been pointed out and feared up until now. Of course, the strength of the long-period earthquake motion will vary depending on the process of destruction at the epicenter, but in any case, it will become the standard for long-period earthquake motion in Tokyo, in the sense that it actually occurred. In the same way, the shaking in central Tokyo in the case of a major earthquake such as the Tokai, Tonankai, or Nankai earthquakes would likely be at a similar level to the shaking this time, considering the relationship between the epicenter and Tokyo. Another problem is that in the feared Tokyo epicenter earthquake, shaking of intensity 6- or 6-upper will be added locally to the shaking this time.

In this earthquake, a maximum seismic intensity of 7 was observed in northern Miyagi Prefecture, and seismic motion of 6-6 and 6-6 was observed in a wide area from Iwate to Ibaraki. I also went to the affected areas immediately after the earthquake to provide support, and in areas that were not affected by the tsunami, structural damage appears to be minimal, in terms of the level of collapse prevention required by the Building Standards Act. However, the actual suffering of the damage and the difficulty of rescue are great. This is because the damage to the interior, facade, and facilities is great, as well as the damage to infrastructure including transportation. There are no concrete measures in place to prevent this damage when subjected to seismic motion of 6-6 and 6-6. It is imperative to clarify what needs to be done to prevent such damage from the damage caused by this earthquake.

Whenever I see the tsunami coming and the situation in the affected areas, I am speechless. Anyway, this is the truth. All we can do is take measures so that we do not forget this.

We must accept the damage caused by this huge earthquake and, based on the facts of what happened, come up with concrete measures to confront earthquakes. We are still in a situation where we must devote all our efforts to providing relief to the victims, but we must also tackle this issue as something that is essential for the development of Japan, a country prone to earthquakes.