By David Jacobson, Temblor

Check your seismic hazard rank

As reported this morning by the Los Angeles Times, the city of Santa Monica, just west of Los Angeles, is poised to undertake the nation’s most extensive retrofitting program. If a law is passed tomorrow by the Santa Monica City Council, as many as 2,000 buildings will have to be retrofitted throughout the city. This program would target not only wooden apartments and concrete buildings, but steel-framed ones as well. Such a move would surpass the regulations held in Los Angeles, which does not require steel-framed structures to undergo a retrofit.

Last December, the Santa Monica City Council held a study session in which seismically vulnerable buildings were identified, and amendments were recommended to the 1999 retrofit standards. The focus of this discussion was to determine ways to ensure that residential and commercial structures are as safe as possible during a large earthquake.

While retrofit programs are common in various West Coast cities (Including San Francisco), the inclusion of steel-framed structures within the Santa Monica initiative makes it unique. Steel-framed structures were once believed to be some of the safest structures. However, in the 1994 Northridge earthquake, numerous steel-framed buildings performed extremely poorly, shocking engineers. Additionally, in the 1995 Kobe, Japan earthquake, some steel building saw floors collapse.

Despite the fact that retrofitting buildings can be expensive, and that steel-framed structures are less vulnerable to collapse than others, according to the 2008 ShakeOut Scenario run by the USGS, the collapse of up to five high-rise steel buildings is seen as possible. Such an occurrence could result in significant loss of life and infrastructure. Because of this, the estimated cost of $5,000-$10,000 per retrofit of wooden apartment buildings, and $50-$100 per square foot in concrete or steel retrofits is seen as minimal in comparison to potential losses. While this cost will be passed to the building owner, depending on the type of structure, various time periods to complete the retrofit will be given. Highest priority structures include unreinforced masonry buildings (2 years to complete) while the lowest are steel structures (20 years to complete).

Based on the likelihood of shaking, and site amplification, Santa Monica has a Temblor Hazard Rank of 53. Additionally, the Global Earthquake Activity Rate (GEAR) model forecasts that a M=6.5-6.75 is likely in your lifetime for the region. Therefore, ensuring the safety of residents is at the forefront of the council’s thinking.

Sources

LA Times

Santa Monica City Government

Caltech/USGS Southern California Seismic Network