The Geotechnical Extreme Events Reconnaissance (GEER) Association has released Version 1.0 of their report for the November 30, 2018, M7.0 Anchorage Earthquake. The GEER Phase I team collaborated closely with a number of other agencies as well as the local geotechnical community to perform their investigation in Early December, 2018. The event was noteworthy for a number of reasons, including the fact that no fatalities were recorded, and that most of the infrastructure damage reported was non-structural. They also note that nearly all of the significant embankment slope failure that occurred along Alaska’s highway and arterial roads were repaired by AKDOT within one week…a remarkable feat. Despite these factors, the report cautions that the event should not be dismissed as an “insignificant event.”
Some of the significant lessons learned that are discussed in the report include:
- Only three instances of structural collapse were observed by the GEER Phase I Team.
- The duration of the event was not long enough to initiate movement on historic landslides from the 1964 M9.2 earthquake.
- Minimal impact to the Port of Alaska, perhaps thanks to recent interim improvements to address corrosion issues.
- The isolated cases of structural damage appeared to be caused by geotechnical issues such as settlement of the foundation or slope deformations.
- Most structural damage occured in areas with significant amounts of organic soils.
- Only isolated instances of soil liquefaction were observed by Phase I team. Additional studies needed in the spring after the snowmelt.
- They observed possible liquefaction issues in improperly placed or insufficiently compacted granular fills which were used to replace over-excavated organic soil. Additional study is needed.
- Several sites in Anchorage that they visited had soil ground improvement and performed well. But the GEER team noted many more sites without ground improvement also fared well.
- The local, state, and federal engineering response to the event was commendable with rapid repair and inspection of facilities.
The report was issued as Version 1.0 on January 2, 2019, and will be followed by a more detailed report (Version 2.0) in early 2019. The GEER Phase 2 investigation team will deploy in the spring of 2019 after snowmelt and will focus on remote sensing and geophysical data collection.
For more info and to download the report, visit the GEER 2018 Anchorage Earthquake page.