Utah Engineers Journal 2021 Issue

49 Figure 4. Population per ~1 sq. km. from LandScan https://earthquake.usgs.gov/earthquakes/eventpage/ uu60363602/pager Continued on the following page Notably, in 2011, the USSC and Structural Engineers Association of Utah (SEAU) published a preliminary survey of K-12 schools. 8 This report highlighted the risk to students’ safety in school buildings and requested funding for additional study from the Utah Legislature. This call for funding went unanswered by the legislature, but the governor’s office offered partial funding in 2015. The effort to find funding to complete the school building survey is ongoing now, 10 years after the report. Leading up to the 2020 Magna earthquake, the largest recorded by modern technology on the Wasatch Fault, the seismic risk to our community is characterized by a few things unique to the Wasatch Front Region: - Unretrofitted unreinforced masonry buildings are common. - National building codes were not enforced reliably across the state until 1980. - The UBC underestimated design forces for the Wasatch Front compared to other high seismic regions such as California (in place until 2001). - Utah is politically averse to regulation; even the state’s parapet bracing ordinance has been subject to attack (Utah Code Section 15A-3-801). - The state does not have any statewide geologic-hazard ordinances related to earthquakes and secondary effects (e.g., surface fault rupture, earthquake-induced landslides, and liquefaction). Misperceptions surround what our building code life-safety standards really deliver to our communities regarding seismic design. Life safety standards aim to provide the likelihood that occupants will be able to escape a building unharmed during an earthquake but do not aim to eliminate damage to the building itself. Any reduction in damage beyond preventing building collapse to the building is a byproduct. In other words, a life safety standard saves lives during an earthquake but does not save the building, nor the meaningful life and the livelihoods we build within those buildings. Our building codes and seismic design are also predicated on the idea that a building’s useful life is 50 years — factoring in the probability the “big” earthquake will happen at a certain location in the next 50 years. Interestingly, though, I have not yet seen a bulldozer show up on-site when a building reaches that age. We should remember what Dr. Lucy Jones, a seismologist and science communication expert, frequently says: it is not a question of if the Big One will occur, but when. Give a building enough time, and an earthquake will affect it. The real question becomes whether we should be building a community that will recover adequately from a potential strong (M W 6.0-M W 6.9) or great (over M W 7.0) earthquake, 9 if not just for our sakes, but also for our children and grandchildren. Upon arriving at my office in Salt Lake on March 18, I felt the parking deck roll underneath me as an MW 4.4 aftershock hit. It was the first of three significant aftershocks I would feel throughout my workday. The office was buzzing with activity — even with less than half of the staff in the office. We received phone call requests for building inspections, and a coordinated effort was established to dispatch our engineers quickly to meet the most pressing needs. Structural engineers all over the county were busily visiting buildings and, in most cases, explaining the extensive damage was largely limited to nonstructural elements. The mainshock, as mentioned earlier, was the largest recorded by modern instruments on the Wasatch Fault. Even though seismologists classify anything from MW5.0-5.9 as a moderate earthquake, shaking intensity registered VII (very strong) on the Modified Mercalli Intensity (MMI) scale. USGS estimates it was experienced by 139,000 people (see Figures 3 and 4). This shaking intensity is a higher one than anticipated for this size event. Seismologists met the first week of February for the 2021 Virtual Utah Quaternary Fault Parameters Working Group Meeting. 10 Participants discussed the causes of the higher shaking intensity, along with the data and research that were generated by the community in the wake of the Magna sequence. According to one seismologist, Ivan Wong, P.G., the event was the best one ever recorded in the Basin and Range Province in terms of the strong motion. Due to extensive instrumentation and data collection, areas of greatest damage can be correlated with the strongest ground shaking. 11