Observations of the Magna Earthquake

Observation of damages

Last month our team shared their observations of the Magna Earthquake during an AIA Utah webinar. While the 5.7 magnitude earthquake was considered moderate, it was a memorable wake up call for preparedness. Here’s a recap of what our engineers shared with 270 attendees.

Measuring an Earthquake
While we’re all familiar with the Richter Scale to describe and measure earthquakes, scientists measure magnitude scales in several other ways. Moment magnitude is the most commonly used and reliable method for measuring an event. It measures how much energy is released by an earthquake. The Modified Mercalli Intensity Scale measures the intensity of shaking produced by an earthquake (instead of the force or strength) and describes how the earthquake is felt by people. The map below highlights what Utahns reported feeling that morning.

Given the variety of experiences we had, we jumped at the chance to install a new seismic monitoring system in our building. Reaveley partnered with Safehub to set up monitors and connect to their web platform in time to record the M4.2 aftershocks on April 16. The monitors also picked up two other events and recorded approximately 2mm of side-to-side movement at our downtown fourth floor office.

University of Utah’s Seismograph Station records the magnitude and duration of earthquakes. While aftershocks are common, most of them were not felt. As of June 24 there have been 2320 aftershocks. We have experienced more earthquakes than you have ever imagined!

Damage Observed
In the days following the earthquake our engineers surveyed building damage to anchors and expansion joints as well as veneer facades. In the mind of the post-earthquake public, minor cosmetic damage like hanging light fixtures, falling hazards, partitions, collapsed ceilings and drywall cracks was unnerving. And while masonry buildings give many of our cities their historic charm, many unreinforced masonry (URM) structures sustained damage. Offices, buildings and construction sites were closed and required inspections before reopening.

Generally we were surprised how such little damage shut down so many structures. The data, photos and reports help to improve building codes, the design and construction of infrastructure and other life safety measures.

Lessons Learned
The quake gave our firm the opportunity to practice our emergency management processes. We know the Wasatch fault zone has the potential for a 7.0M event – which would release at least 100 times the energy of the Magna Earthquake and result in significantly more damage. ATC-20 is a procedure used to standardize building assessments following an event. Utah adopted this system and training is performed by the Utah Department of Emergency Management and includes two classes of inspectors, one of which requires structural engineering licensure.

It’s estimated over 300,000 building inspections will be required after a major earthquake. That would necessitate roughly 2400 inspection teams. Right now Utah has approximately 200 certified inspectors (including many of our engineers). There is clearly a need to have more qualified professionals ready to perform evaluations and decisions requiring continued use and occupancy of damaged buildings. The lessons of the recent earthquake, coupled with the COVID-19 pandemic, have provided real reminders of the importance of emergency preparedness. The biggest lesson remains the need to reduce the risk of disasters before they happen and to prepare for them more systematically, not just to respond to them afterwards.