A recent survey of large buildings in Japan built prior to 1981 has found that the status of earthquake retrofitting for about 70% of buildings surveyed is either unknown or insufficient. This is according to the results of an audit recently released by the Japanese government’s Board of Audit and reported by the Mainichi newspaper.
The audit specifically looked at large buildings, such as hospitals, schools, and hospitals compliant with pre-1981 building codes (known as kyuu-taishin earthquake building standards) which are not as stringent as those implemented after 1981 (known as shin-taishin earthquake building standards). All buildings surveyed had already been identified as being in need of seismic reinforcement.
It was found that the number of buildings for which the actual seismic retrofitting status was reported as unknown by local governments, had increased to over 20% in the last five years. Local governments are responsible for reporting the status of earthquake retrofitting under the 2013 Revised Act on the Promotion of Seismic Improvement. The law requires that owners of large buildings built prior to May 1981 inspect their buildings for earthquake resistance and take retrofitting measures if necessary.
In the audit, about 50% of buildings surveyed were found to have had no earthquake retrofitting measures implemented, for a total of about 70% of buildings with a status of either “unknown” or “insufficient”.
3,800 buildings with “high” or “existing” chance of collapsing in a major quake
The Board of Audit surveyed 5,000 large buildings in 14 prefectures centered around the Tokyo metropolitan area whose owners had received government assistance in the last five years for earthquake retrofitting. Government subsidies are meant to be used to ascertain the actual degree of earthquake resistance of private buildings and to help owners upgrade buildings if necessary.
The audit identified 3,800 buildings that either had a “high” or “existing” risk of collapse in an earthquake with an intensity of “6”or “7”on the Japanese earthquake scale. In Japan, the Japan Meteorological Agency (JMA) measures seismic activity in units of shindo (震度, seismic intensity, “degree of shaking”). The shindo scale or JMA scale describes the degree of shaking at various points on the earth’s surface, not the amount of energy released by the earthquake. Seismic activity is divided into ten levels from zero to seven.
Of the 3,800 high risk buildings,
- 1,300 buildings had completed seismic retrofitting or are in the process of being retrofitted.
- The owners of 1,500 buildings had received some form of government aid but had not yet implemented any seismic retrofitting measures (but may have formulated a plan for doing so).
- Local government authorities were unable to ascertain the actual status of retrofitting for 1,000 buildings. Of these 1,000, the authorities were unable to contact the owners of 600 buildings. Of the 400 who could be contacted, 75% of owners said that they had not implemented any seismic retrofitting measures.
The Board of Audit will make recommendations to the Ministry of Land with an eye to having the Ministry give more guidance and help to local governments so that they can better ascertain the actual status of seismic retrofitting for large buildings under their jurisdiction.
Pre-1981 earthquake building codes
Prior to 1981, buildings only had to be designed to withstand major damage from a quake registering 5 on the Japanese earthquake scale.
Buildings designed after 1981 have to be built to withstand major damage from a quake registering 6-7 on the Japanese earthquake scale. More specifically, buildings which received their Construction Confirmation Certificate (建築確認済書) before June 1, 1981 are subject to the old earthquake standards. In addition, under the new standards buildings constructed after 1981 must be designed not only to withstand shocks to the building itself, but also with an eye to lowering the potential harm to life and limb from a quake.
You may also be interested in: Earthquake buildings codes in Japan – What you need to know
Source: Mainichi shinbun, October 8, 2019
Lead image: Earthquake retrofitting, via smile.re-agent.info