A recent estimate by a government panel in late 2013 reported that a magnitude-7 earthquake directly under Tokyo could destroy as many as 610,000 buildings in Tokyo and the neighbouring three prefectures. 70% of the affected buildings could be destroyed by fires that quickly spread through densely packed neighbourhoods.
Many of the Olympic events are centred around the islands in Tokyo Bay. While they may be spared from the risk of fire due to the open space, these man-made islands can suffer damage from liquefaction and are even at risk of being submerged by a tsunami. A working group from the Cabinet Office's Disaster Management Group are requesting that urgent measures be taken to reduce the risk of any damage and to make sure that the Olympics can be held without disruption.