2018 M7.1 Anchorage Earthquake

This earthquake was felt widely across Alaska. Significant damage occurred in Anchorage, Eagle River, and throughout the Mat-Su Valley. The earthquake caused power outages, damage to roads and buildings, and closures of schools, businesses and government offices. While there were no fatalities, there were several cases of nonlife-threatening injuries.

The shaking varied widely depending on the geology of the region. The graphic below shows the variability in shaking across the Anchorage Bowl.

The graphic below compares instrumentally derived values (triangles) with USGS "Did you feel it?" reports (circles) for the Anchorage Bowl (left) and Eagle River (right).

Although shaking caused some direct structural damage, most damage appeared to be tied to foundation damage resulting from ground failure. The most common structural damage included foundation damage, wall cracking in wood and masonry buildings, and walls offset and disconnected from floors.

Damage to the region’s inventory of 245 bridges was generally minor. Twenty bridges were identified by the Alaska Department of Transportation as having more significant damage. Common bridge damage included shifting girders, damage to shear keys, bent anchor bolts, and damage to the grout pads under bearings. Less common bridge damage included cracks in abutments and settling under approach ramps. The earthquake caused widespread nonstructural damage to highway road paving and substructures. Despite winter conditions pavement damage was generally repaired quickly, though much of this work will be redone at a later date under warmer conditions.

It is generally acknowledged that structures built to building code standards fared better during this earthquake. More research is needed to identify the factors that contributed to the higher rates of damage to structures outside the Anchorage Bowl, including the influence of soils.

SOURCE: West, et al. (2019) The 30 November 2018 Mw7.1 Anchorage Earthquake, SRL, https://doi.org/10.1785/0220190176