One of the primary concerns for public safety in Tokyo is the expectation of the next big earthquake, which is overdue considering large quakes occur every 70 years on average and the last was in 1923. Earthquake drills are held on the anniversary of the 1923 earthquake, when people are reminded to turn off open flames and take proper shelter. Open spaces in the form of parks are maintained throughout the city to accommodate expected populations rendered homeless by a quake.