What happened
On 1 September 1923, just before noon local time, the plate boundary beneath Sagami Bay south of Tokyo ruptured. Many households were cooking lunch over open fires, and strong winds spread the flames through the wooden buildings of Tokyo and Yokohama. More than 100,000 people died in the fires, collapses and tsunami. In the chaos that followed, Koreans living in Japan were also massacred. The anniversary of the earthquake is Japan's Disaster Prevention Day.
How to read these data
Magnitude measures the energy released at the focus: each step is about 32 times more energy, so an M 9 earthquake releases about a thousand times more energy than an M 7. Its effects, however, also depend on focal depth, distance to cities, ground conditions and building quality – a shallow M 7 beneath a city can be deadlier than a deep M 8 under the ocean.
For earthquakes before the era of dense seismic networks, location, depth and magnitude are estimates from later analyses of records and accounts (e.g. the ISC-GEM catalogue).
Data: USGS ComCat (iscgem911526) · Wikipedia (pl) · Wikipedia (en)