Using the M7.0 Anchorage Earthquake to Validate Ground Response Modeling at the Delaney Park Downhole Array in Anchorage, Alaska

Date: 4/26/2019

Time: 01:45 PM

Room: Cascade II

On November 30, 2018 Anchorage, Alaska was struck by a M7.0 earthquake, the largest earthquake since the 1964 Great Alaska Earthquake to shake Anchorage. Numerous strong motion instruments recorded the earthquake, including the Delaney Park Downhole Array (DPDA). The DPDA consists of seven strong motion three-component accelerometers at depths ranging from the surface to 61 meters below ground. It is located in downtown Anchorage, near where significant ground failure occurred in 1964. Significant improvements related to modeling ground response at the DPDA have been achieved by the authors over recent years to better estimate ground shaking at high intensities despite the absence of observations from such events. Thanks to the data collected during the 2018 earthquake at the DPDA a comparison can now be made between the model, calibrated with earthquakes of lower intensity, and the observations in the 2018 event. The largest ground motion measured at DPDA prior to November 30, 2018 was from the M7.1 Iniskin Earthquake on January 24, 2016, which was over 200km from Anchorage. Comparisons in site response among the Anchorage, Iniskin and other recent earthquakes is presented with consideration to site response modeling, with a focus on the transfer function.

The DPDA site model leads to a good fit of the large earthquake ground motion response and gives greater confidence in the analysis of site response within downtown Anchorage. There are some limitations to the equivalent-linear model with respect to nonlinear behavior of soil in large earthquakes where larger shear strains are developed. An evaluation of the modeled response with respect to estimation methods for nonlinear effects utilizing recent strain proxies is presented. The results of these evaluations create the groundwork for changes proposed to local building codes related to slope stability analysis within Anchorage.

Presenting Author: John Thornley

Authors