Prepare for a magnitude 6-6 earthquake

Regarding the situation and damage caused by a magnitude 6-low earthquake, the Japan Meteorological Agency explains that it would be "difficult to stand," "heavy, unsecured furniture would topple or move," "doors would have trouble opening and closing," "exterior wall tiles and glass would break or fall in many buildings," "cracks and destruction in building walls and pillars," "interruption of infrastructure supplies," and "occurrence of ground fissures and landslides." The current Building Standards Act assumes two levels of earthquake motion strength, and aims to ensure no damage in rare earthquakes, and to avoid fatal damage such as collapse in extremely rare earthquakes. From this, the reality of earthquake-resistant design for a magnitude 6-low earthquake can be roughly stated as follows: both new buildings and existing buildings that have been reinforced to be earthquake-resistant will avoid fatal damage such as collapse, but various types of damage are possible.

However, not all buildings suffered severe damage, and some only suffered minor damage. For example, buildings with seismic isolation structures and high-rise buildings designed to limit the elasticity of their structures and suppress inter-story deformation against a maximum speed of 25cm/sec. also suffered little damage. Buildings that have been designed with storm countermeasures in place and therefore have a margin of resistance against earthquakes, and buildings designed with high seismic resistance ratings based on the Quality Assurance Act also suffered little damage. Furthermore, there are regions, such as Shizuoka Prefecture, that require high earthquake resistance as a measure against the Tokai earthquake.

However, it is important to note that the goal of earthquake-resistant design is centered on the structure. If the structure is undamaged, the deformation of the building will generally be small, and damage to the finishes, equipment, and furniture supported by the structure is expected to be small as well. However, breakage or movement or toppling of these items may cause human injury or hinder recovery efforts.

Regarding the probability, it goes without saying that we must prepare for areas with a high probability, but what about areas with a low probability? The Headquarters for Earthquake Research Promotion considers a probability of occurrence of 3% or more to be high, and 0.1% to 3% to be somewhat high, so in the end, we are forced to think that an earthquake will occur in most areas.

To summarize the above, preparations for a magnitude 6-6 earthquake should be: (1) when building new buildings, consider measures to prevent damage from a magnitude 6-6 earthquake, (2) immediately implement seismic reinforcement for buildings that require it, and (3) for all buildings, take earthquake-proofing measures for furniture, fixtures, finishes, doors, and equipment other than the structural components, or take soft measures to ensure that damage to these items is not linked to man-made disasters and to recover quickly. The more likely an earthquake is to occur, the more urgent this should be.

Companies are now working on business continuity plans (BCPs) related to earthquake risks. These are truly preparations for a magnitude 6-low earthquake from both the hard and soft aspects. Progressive condominium management associations have also begun similar initiatives as life continuity plans (LCPs). Expert organizations such as the NPO Earthquake Safety Organization have also begun to support such comprehensive measures. Furthermore, if emergency earthquake warnings function effectively, even a few seconds of grace is expected to be effective in reducing human damage.

In the event of a magnitude 6.0 earthquake, which is sure to occur at some point, we in the construction industry will support building owners and managers in taking measures, and will also work to increase the preparedness of those around us.

After I wrote this article, a major earthquake caused devastating damage in Sichuan Province, China. Although the situations in China and Japan are different, I think this has reminded us of the importance of preparing for major earthquakes.