It has been 17 days since the Noto Peninsula earthquake. The full extent of the damage to buildings is still unclear. One noticeable feature is the collapse of wooden houses in succession in areas where seismic intensity 6 or higher was observed. However, there is one place where the situation is different. Shika Town, Ishikawa Prefecture, recorded a maximum seismic intensity of 7. Looking at residential areas, despite the strong shaking, the buildings themselves have not collapsed. What is the reason for this? Professor Sakai of the Kyoto University Disaster Prevention Research Institute, who investigated on the ground, is focusing on the "period of the shaking" recorded by the seismometer. Professor Sakai Yuki of the Kyoto University Disaster Prevention Research Institute: "The place where the seismic intensity 7 was recorded is K-NET Tokuyoshi, but here the period is very short at 0.2 seconds, so five round trips per second, very fast, or rather, it was a shaky shake. This type of shaking increases the seismic intensity, but does not lead to major damage to buildings." "Short-period vibration" that occurred locally. On January 1, an experiment was conducted to reproduce the shaking based on the waveforms observed at four locations in Noto. The three locations of Wajima City, Suzu City, and Anamizu Town shook greatly back and forth and side to side, while Shika Town shook more in small increments. In this earthquake, vibrations with a period of 1 to 2 seconds were observed in various places, including Wajima City and Anamizu Town. This type of vibration has the characteristic of easily collapsing wooden houses and low- to mid-rise buildings, and is said to have led to the expansion of damage in the Great Hanshin-Awaji Earthquake. However, this type of vibration was not observed in Shika Town. Professor Sakai points out that the difference in damage may be due to the hardness of the ground. Professor Sakai Yuki of the Disaster Prevention Research Institute, Kyoto University: "It is said that the period of the shaking is determined by the product of the epicenter, the propagation path, and the surface ground, but the influence of the surface ground is quite large, and the ground in Shika Town is hard. The fact that it is hard means that the ground itself has a very short period, so short periods are likely to occur." Professor Sakai had another impression during the field survey. When I saw the scene in Anamizu Town. Professor Yuki Sakai, Disaster Prevention Research Institute, Kyoto University: "My first impression was that the damage was terrible, but in contrast, there were many buildings that were almost completely empty next to the collapsed and completely destroyed buildings. The earthquake resistance standards were revised in 2000, and these buildings were probably built within the last 20 years, so they were probably built after that." "2000 Earthquake Resistance Standards". This story comes from the Great Hanshin-Awaji Earthquake. On the 17th, 29 years ago, 64% of houses built to the "old earthquake resistance standards", which were designed to withstand a seismic intensity of 5, suffered severe damage. Furthermore, damage was also sustained in wooden houses built to the "new earthquake resistance standards", which were designed to withstand a seismic intensity of 6+, so another level of higher standards were created. That was the "2000 Earthquake Resistance Standards". Wooden houses built after 2000 were required to reinforce joints such as pillars with metal fittings and to be designed according to the condition of the ground. This may have been the reason for the difference in the collapse of houses in Anamizu Town. Professor Sakai has a reason for pointing this out. The Noto Peninsula was hit by an earthquake in 2007, and it is said that nearly 20% of wooden houses in Anamizu Town collapsed. It is believed that many of the houses in the town today are new buildings that were built after that, that is, houses built after 2000. Professor Sakai Yuki of Kyoto University Disaster Prevention Research Institute: "(Q. Was there less damage to buildings after the new standards) Rather than saying that there was less, I get the impression that there was 'overwhelmingly less.' The most important thing to avoid is 'collapse.' Although the methods for meeting the 2000 standards and for seismic reinforcement are different, they are the same in terms of increasing seismic performance, so if we do this, we may be able to avoid major damage even if an earthquake of this magnitude occurs. I would like you to consider this in the future." [TV Asahi News] https://news.tv-asahi.co.jp