Initial Observations From the GEER Reconnaissance Evaluation of the 2018 M7.0 Anchorage Alaska Earthquake

Date: 4/26/2019

Time: 01:15 PM

Room: Cascade II

The 2018 M7.0 Anchorage Alaska earthquake occurred on November 30^th and was located 11.3 km north of the city at a hypocentral depth of 40 km. Widespread damage reported in the media prompted the Geotechnical Extreme Events Reconnaissance Association (GEER) to rapidly mobilize a team to the affected area to assess general patterns of damage to better understand earthquake effects. The main objectives were to document perishable geotechnical and geologic data and evaluate lessons learned from the event. Close collaboration with municipal, state, and federal officials, as well as the local geotechnical engineering community greatly assisted the GEER team’s efforts and highlights the importance of open communication during the immediate post-event response and recovery period.

Here we present the GEER team’s initial observations from reconnaissance surveys conducted between December 8 and 15, 2018. Damage was characterized based on field mapping and aerial drone photogrammetry at sites within the affected area. We assessed damage to highway embankment slopes and bridges, sites with geotechnical ground improvements, sites with nearby ground motion recording stations, sites of critical infrastructure (e.g., Port of Alaska, Port Mackenzie rail expansion project), and sites impacted by settlement, liquefaction and/or slope failure. The observations indicate that the majority of the infrastructure damage was related to localized liquefaction in granular fills beneath structures, slope instabilities in native slopes and anthropogenic fills, and bearing capacity failures in organic soil deposits due to cyclic softening. Within a week of the event, highway and road bridges had been inspected, major highway embankment damage had been repaired, utility services had been mostly restored, and structural repairs to many residences were underway highlighting the effectiveness of the engineering response and the resiliency of the Anchorage region.

Presenting Author: Rich D. Koehler

Authors