City of Hiroshima finds parts of A-Bomb Dome vulnerable to earthquakes

by Aya Kano, Staff Writer

On January 29, the City of Hiroshima announced the results of its computer analysis of the Atomic Bomb Dome’s ability to withstand earthquakes. The A-bomb Dome, a World Heritage site located in downtown Hiroshima, is reportedly not in imminent danger of collapse in the event of an earthquake measuring a lower 6 on the Japanese 7-point seismic scale. But it has been discovered that some portions of the walls could be vulnerable if a tremor should strike. In April, samples will be collected by cutting into the walls. Based on a close examination of these samples, a decision will then be made whether thorough seismic retrofitting is required.

In fiscal 2007, the city carried out an investigation on the seismic resistance of the dome. Using the data obtained through that investigation, the first computer analysis of the structure was conducted from January to October 2012. For this analysis, three conditions were simulated: the Geiyo Earthquake of March 2001 (intensity of lower 5 on the Japanese scale); a strong earthquake that is likely to occur within 30 years (intensity of upper 5); and the maximum scale among those expected to occur in the city (intensity of lower 6).

It has been found that four areas not supported by beams may suffer stress in the event of an earthquake, resulting in cracks or other damage. However, since the dome endured the Geiyo Earthquake without incident, city officials believe that the epoxy resin injected into the walls during previous preservation efforts has been effective.

The city has decided that samples will be collected from the walls of the four areas in April, and the effects of the past preservation work will be evaluated by testing the strength of the bricks and the condition of the resin. Based on these findings, a decision will be made on whether full-scale measures to strengthen the dome are needed.

“For the time being, we needn’t be worried about the safety of the dome,” commented Hiroshima Mayor Kazumi Matsui. “But we do need to carry out detailed inspections to determine if reinforcement work is necessary. These inspections will be completed by the 70th anniversary of the atomic bombing.”

The A-bomb Dome was designated a historic site by the Japanese government in 1995, and in 1996, it was added to the list of UNESCO World Heritage sites. In fiscal 2005, the City of Hiroshima decided to defer a large-scale repair project and maintain the current state of the dome until at least the 100th anniversary of the bombing.

(Originally published on January 30, 2013)