What happened
Before dawn on 17 January 1994, local time, a “blind” fault that does not reach the surface slipped beneath the San Fernando Valley. Sections of freeways, multi-storey car parks and an apartment building in Northridge collapsed. Around 60 people died – few, because the shock struck at four in the morning on a public holiday. Losses ran into tens of billions of dollars. Cracked welds in steel-frame buildings forced changes to US structural codes.
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.
Data: USGS ComCat (ci3144585) · Wikipedia (pl) · Wikipedia (en)