All of Iran lies within a major earthquake zone, and the country has suffered terrible temblors before. But a similar quake in the congested capital of Tehran would be a shattering catastrophe. Unlike building codes in other endangered cities such as San Francisco and Tokyo, Tehran's are relatively lax, and many residents live in the sort of unreinforced-concrete houses that turn into death traps in the event of a strong quake. The Iranian Health Ministry once estimated that a 7-magnitude quake would destroy 90% of the city's hospitals.
Cascadia sits on top of major faults, and although it doesn't get hit very often, the region has seen massive quakes before. The geologic record indicates that a catastrophic quake hits Cascadia only about every 500 years, but the cities of the Pacific Northwest, like Seattle and Vancouver, are far less prepared than San Francisco and Los Angeles for a major earthquake, so when the next powerful temblor comes around, the region could suffer.