The Golden Gate Bridge

1994 Northridge Quake

TIME   January 17, 1994 / 4:30 am PST

LOCATION 20 miles west-northwest of Los Angeles, 1 mile south-southwest of Northridge. Along with the Northridge Thrust (also known as Pico Thrust) several other faults experienced minor rupture.

MAGNITUDE  6.7

HUMAN/PHYSICAL TOLL $44 Billion in damage, 25,000 Dwellings uninhabitable, 9 Hospitals closed (loss of 2,500 beds), 9 parking garages collapsed and major freeways collapsed. Moment steel frames suffered huge, unexpected cracks.

LESSONS LEARNED The January 17, 1994 Northridge Earthquake was the most damaging earthquake in the United States since 1906, and overturned a number of assumptions on earthquake science and engineering. First, the earthquake occurred on a previously unrecognized fault and shaking from the earthquake caused the fracturing of buildings previously considered protected from earthquake-related damages. Direct economic losses from the Northridge earthquake were in excess of $40 billion.

Northridge Earthquake
Car is crushed under the collapsed building
The problems that surfaced with respect to welded steel frame buildings, wood frame housing, and building and business losses galvanized partnerships between universities, industry, and government to investigate and provide answers to the questions that were generated by the earthquake’s effects.

The consequences of these collaborative activities were improved codes, inspection procedures, and construction practices for steel and timber buildings.

Most notable was the discovery of widespread welding failures at the beam-column connections of steel moment resisting frame structures. As a result, input ground motions used in building design were modified to reflect the experience of the earthquake, and Structural Engineers established design and detailing requirements for steel moment resisting frame structures.

While inspection and quality procedures have been upgraded and new standards developed for the design and retrofit of pre-existing buildings, regulatory wheels turn slowly. Some elements of the legacy of Northridge are still working their way through the code regulatory bodies.

Sources: Southern California Earthquake Data Center, UC Berkeley/NISEE