Dear Tom,

What major city in the world is most threatened by an earthquake?

—Kenny Millert, Rockford

Dear Kenny,

Any city that has experienced a major earthquake might seem to qualify as the world’s most earthquake-threatened city, but some places are struck more frequently. A strong case can be made that Tokyo, Japan, is the world’s most earthquake-threatened city. The population of metropolitan Tokyo is about 37.5 million; the city proper, 14 million. Japan lies in the earthquake-prone “ring of fire” that surrounds the Pacific Ocean. Tokyo has experienced a major earthquake about every 65 years, and its last major quake struck on Sept. 1, 1923—nearly 99 years ago. This means the city is alarmingly overdue for a major earthquake. The 1923 catastrophe claimed 143,000 lives.