According to the Japan Wood-frame House Earthquake Reinforcement Business Cooperative, made up of contractors and architects that provide earthquake-retrofitting services, 93% of the 4,000 homes that have had earthquake-resistance inspections carried out over the past 15 years in Tokyo were at risk of collapse in an earthquake that produced a seismic-intensity (shindo) level of upper 6 or higher (*Note: The seismic intensity scale is difference to magnitude). The average age of a house surveyed by the Cooperative was 37 years.