Recent Recorded California Earthquakes
California is no stranger to earthquakes and the San Francisco area has certainly seen some powerful quakes over the years. The San Francisco area has experienced seven earthquakes in the last seven days and thirty-two in the last 30 days, which is essentially an earthquake a day (earthquaketrack.com). Although these quakes are not of a particularly high magnitude, their frequent occurrences still call for attention to be paid. In addition, although it is not a recent earthquake, it is important to remember the historical 1906 San Fransisco earthquake. With a magnitude of over 7.7, this earthquake was extremely destructive in San Francisco and the surrounding areas. This quake has gone down in history as being one of the worst in United States history, when considering the damage caused and the lives that were lost as a result. The 1906 is still to date the largest quake that has occurred in the San Francisco area. Many Californian’s may be thinking, “accompanying all of these frequent and small earthquakes must be the big one as well too right?” The answer is yes! It is a general understanding from various scientific outlets such as the USGS and academic studies that another high magnitude and destructive quake could come at any time. This consensus is what has driven policies regarding mandatory soft-story and non-ductile seismic retrofitting in San Francisco and Berkeley. Mandatory seismic retrofit ordinances have already begun and are actively being implemented and now and for the next twenty plus years. Greater recognition of the importance of seismic retrofitting has been made possible through the efforts of many earthquake experts and structural engineers over the last decade. These experts, although sometimes ignored historically, have been explaining for some time that the frequency and unpredictability of California quakes combined with deficient infrastructure is why seismic retrofitting should no longer be voluntary, but mandatory. The preventive measures of seismic retrofitting that is now required in many cities in California will be to the benefit of all, when inevitably a larger and more powerful earthquakes hits the state.
Industry News for Seismic Retrofit Service for San Francisco
The San Francisco Community Action Plan for Seismic Safety (CAPSS) estimated back in 2013 that “43 to 85 percent of the most vulnerable multi-unit, wood-frame buildings would be posted with a red UNSAFE placard (“red tagged”) following a magnitude 7.2 earthquake on a nearby segment of the San Andreas fault, representing 1,200 to 2,400 red-tagged buildings. Red-tagged buildings are uninhabitable and may not be occupied after an earthquake until they are either repaired or replaced… The CAPSS study estimates that with appropriate seismic retrofit the overall rate of collapse in a 7.2 San Andreas fault earthquake drops dramatically.” (Per the San Francisco Ordinance No. 66-13)
In the event of an earthquake there has to be some type of system to evaluate how well a building will hold up. One such rating system is known as the United States Resiliency Council Building Rating System. Per the USRC website, “The USRC Building Rating System assigns one to five stars for three performance measures – Safety, Damage expressed as repair cost, and Recovery expressed as time to regain basic function.”
It is the discretion of the owner to what level of resiliency they desire for their building. At minimum, the seismic retrofit ordinances aim to make buildings safe enough for tenants to exit the building safely in the event of a large earthquake. This does not guarantee that the building will be habitable after an earthquake. For other buildings that would in fact need to be in operation after a large quake, i.e. hospitals, these buildings must be kept to a higher standard of resiliency.
Every city should be concerned first and foremost about the safety of its residents, but secondly, they should want to make sure that the City would still be able to thrive after an earthquake. Would the residents be able to return to their homes and/or jobs after a quake, or will they move to an area of less seismic activity? Per www.fema.gov/building-codes, “If you live or work in retrofitted structures, you’re less likely to be injured during an earthquake. After the earthquake, you’re also more likely to have a home and a job to which you can quickly return. Businesses that use retrofitted buildings are more likely to survive damaging earthquakes and to sustain shorter business interruptions and fewer inventory losses.”
April 14, 2017