<Tr> <Th> Peak acceleration </Th> <Td> 1.82g horizontal </Td> </Tr> <Tr> <Th> Casualties </Th> <Td> 57 killed> 8,700 injured </Td> </Tr> <P> The 1994 Northridge earthquake occurred on January 17, at 4: 30: 55 a.m. PST and had its epicenter in Reseda, a neighborhood in the north - central San Fernando Valley region of Los Angeles, California . It had a duration of approximately 10--20 seconds . The blind thrust earthquake had a moment magnitude (M) of 6.7, which produced ground acceleration that was the highest ever instrumentally recorded in an urban area in North America, measuring 1.8g (16.7 m / s) with strong ground motion felt as far away as Las Vegas, Nevada, about 220 miles (360 km) from the epicenter . The peak ground velocity at the Rinaldi Receiving Station was 183 cm / s (4.09 mph or 6.59 km / h), the fastest peak ground velocity ever recorded . In addition, two 6.0 M aftershocks occurred, the first about one minute after the initial event and the second approximately 11 hours later, the strongest of several thousand aftershocks in all . The death toll was 57, with more than 8,700 injured . In addition, property damage was estimated to be between $13 and $50 billion, making it one of the costliest natural disasters in U.S. history . </P> <P> The earthquake struck in the San Fernando Valley about 20 miles (31 km) northwest of downtown Los Angeles . Although given the name "Northridge", the epicenter was located in the community of Reseda; it took several days to pinpoint the epicenter in detail (both communities are neighborhoods of the City of Los Angeles). This was the first instance with a hypocenter directly beneath a U.S. city since the 1933 Long Beach earthquake . </P>

What was the magnitude of the northridge earthquake