By Heather Haffener with contributions from Amy Mestas, SE, PE
On the morning of November 30, 2018, the earth awoke the residents Southcentral Alaska with a 7.1 magnitude earthquake. For Anchorage, it was the second-largest earthquake to strike the area in the short time it has been a city. After the quake, the hard part was over for many and the only recovery was cleaning broken glass, straightening photos, and calling loved ones. For PDC Engineers the work was just beginning. As the hours passed that morning, more and more phone calls began to come into the Anchorage office.
PDC’s structural engineers responded immediately after the event, quickly beginning to evaluate the damage done to commercial and residential structures. Post-quake cracks and displacements appeared in walls, ceilings, foundations, and roofs that needed to be inspected to determine the scope of the effects. Of the damage witnessed, the most extensive was caused by ground failure and liquefication. Ground failure is responsible for landslides, slope failure slides, and lateral spread. Liquefication is a result of certain types of susceptible soils being water-saturated during an earthquake, causing it to act as a fluid.
The most common failures identified across the Anchorage Municipality were:
- ceiling grid damage caused by improper installation
- improper compaction of soil leading to foundation settlement
- masonry damage to older buildings not meeting current codes
- failed roof and wall connections
The majority of the structural damage sustained that deemed a property unsafe to inhabit was located in Chugiak or Eagle River; only two instances were recorded in Anchorage. Much of this can be linked to a lack of construction inspections and building codes outside of the Municipality of Anchorage. As a result, members of PDC’s structural team are working through the Structural Engineers Association of Alaska and with the Chugiak/Eagle River community to develop a review and inspection program for residential and commercial construction as required by the International Building Code.
One year later, inspections are still taking place and repairs continue to be made. However, even with all the work to correct the effects of the earthquake, there is a strong chance that additional damage is hiding behind the sheetrock and exterior siding. Given the seismic history of Alaska, a more serious earthquake can be expected at some point prompting structural engineers and property owners alike to be wary.
PDC’s Senior Structural Engineer in Anchorage, Amy Mestas, notes that structures are not designed to hold up to multiple design level earthquakes. Rather, when built to code, their primary function is to protect life and allow occupants to escape safety. The more a building suffers from aftershocks or additional earthquakes, the weaker its structure may become. She further notes that last year’s event should be a wake-up call, not a sigh of relief that it has passed. A larger earthquake could cause much more damage and anything not addressed from the last event could suffer greatly.
PDC’s earthquake response team has been presenting the information gathered from their building inspections at a variety of conferences and public meetings over the past year with the ambition of better educating the public about the effects of the November 30th earthquake.
Through this and other means, PDC continues to be an ardent supporter of stronger code requirements for the construction of new buildings in Southcentral Alaska.
If you are hosting a conference or other organizational event and would like to feature one of PDC’s engineers to speak in regards to the 7.1 earthquake of 2018, please call us at (907) 743-3200.