United States

Southern California

Regional

6.7 M_w

1.8 g

The 6.7 Mw Northridge earthquake struck the Los Angeles region shortly before dawn on Monday Janury 17, 1995. It was caused by the sudden rupture of a previously unknown, entirely subsurface, 'blind' thrust fault. The system of blind thrust faults to the north of the Los Angeles basin is caused by north-south compressive stresses imposed by the 'big bend' of the San Andreas Fault system that marks a principal focus to the North America-Pacific boundary.

The are of strongest shaking in the Northridge earthquake was about 30 miles in diameter, encompassing southern Ventura and northern Los Angeles counties: a highly urbanized region in which a large inventory of buildings and structures were exposed to intense shaking.

10 - 100

1,000 - 10,000

> 100 M USD

The earthquake was the most destructive earthquake in the US sine the 1906 San Francisco earthquake. Overall about 4,000 buildings were severely damaged or destroyed and another 8,500 were moderately damaged.

Seven major freeway bridges in the area collapsed, and 170 were damaged, disrupting traffic in the Ventura-Los Angeles region for weeks following the earthquake.

Communication, water and power distribution systems were also affected.

The earthquake highlighted the vulnerability of apartment complexes built over parking garages (buildings with a 'soft' story). Many of these buildings sustained significant damage due to failure of columns at the parking level. Several precast tilt-up structures were also badly damaged due to the collapse of tilt-up walls. Nine parking structures collapsed, and nine hospitals had to be closed immediately after the earthquake. While much less visible than the collapses, many large steel frame buildings suffered significant cracking in their principal beam connections.

Although limited in their extent, several fires broke out, including one that burned seventeen homes in a mobile home park.

Considering its close proximity to the densely populated areas of downtown Los Angeles, the event had a relatively low mortality (57 people).

However, the economic losses estimated at $49.3 billion ($41.8 billion in direct economic loss and $7.5 billion in indirect economic loss) were the largest ever experienced from a natural or man-made disaster in the US.