A pair of major earthquakes shook Southern California over the weekend, and while the damage wasn’t as bad as it could have been in a more populated area, many were left thinking, “Is the big one coming next?” Thursday’s 6.4 magnitude earthquake was followed by a 7.1 magnitude earthquake on Friday, both originating 11 miles outside of Ridgecrest, Calif., a city with a population of nearly 29,000 as of 2017 U.S. Census Bureau data. However, Friday’s earthquake could be felt as far as Las Vegas.
According to Desert Sun, roads and buildings suffered the most damage, with glass blown out of some buildings in Kern County, Calif. A representative for Kern Glass in Bakersfield, Calif., said the company hasn’t received any calls about broken glass due to the earthquake. 702 Glass & Windows, a glass shop based in Las Vegas, wished people well on its Facebook page and asked people to give them a call if any windows, glass or mirrors needed to be replaced. When USGNN™ reached out to the company inquiring if they’d yet received any calls, a representative said they had not.
Many areas along fault lines in California are assessing their own situations in case of a major earthquake. According to NBC 7 San Diego, the San Diego County Office of Emergency Services used a FEMA disaster evaluation model to determine damage estimates for a 6.9 magnitude earthquake along the Rose Canyon fault line, which runs through San Diego County. The model estimated that an earthquake of that size would cost nearly $1.1 billion in structural damage and around $5.3 billion in non-structural damage, which includes glass.
The American Architectural Manufacturers Association (AAMA) recently updated two documents related to seismic drift, AAMA 501.4-18, Recommended Static Test Method for Evaluating Window Wall, Curtain Wall and Storefront Systems Subjected to Seismic and Wind-Induced Inter-Story Drift, and AAMA 501.6-18, Recommended Dynamic Test Method for Determining the Seismic Drift Causing Glass Fallout from Window Wall, Curtain Wall and Storefront Systems.
While AAMA 501.4 provides a means of evaluating the performance of windows, window wall, curtainwalls and storefront systems when subjected to specified horizontal displacements in the plane of the wall, AAMA 501.6 focuses on determining the horizontal racking displacement amplitude of exterior wall system framing members that would cause fallout of representative architectural glass panels under controlled laboratory conditions, according to the organization.
JA Weir Associates principal Jon Weir says, “Recent earthquakes have us all reminded of where we live and what the future holds. Current code is solid on what we have to do to design not only the building structures, but also the exterior facades. We work directly with the engineers who design the structure and have to meet specific criteria set forth by the state and local municipalities. Overall expectations for the performance of an exterior wall under an inelastic seismic event (typically a 2% earthquake) is that we do not even break glass. Of course, this is for new structures so older buildings can have lesser performance.”