The M7.0 November 30, 2018, Anchorage, Alaska, Earthquake and Response of the USGS Earthquake Hazards Program

Date: 4/26/2019

Time: 02:15 PM

Room: Cascade II

The November 30, 2018, Mw 7.0 earthquake near Anchorage, Alaska, occurred as the result of normal faulting at a depth of about 40 km. The locations and mechanisms of the mainshock and its aftershocks indicate that rupture occurred on an intraslab fault within the subducting Pacific slab, rather than on the shallower subduction interface between the Pacific and North American plates. Descriptions of the mainshock and associated hazards were quickly posted to the Earthquake Hazards Program event page, including two new products: aftershock forecasts and ground failure forecasts. The Anchorage area is relatively well instrumented with seismometers and accelerometers, including in a number of tall buildings and other structures. These seismic sensors generally performed well, recording a maximum acceleration of about 0.55g. Additional temporary seismic stations were deployed in the days following the mainshock in an attempt to better understand the effects of the Anchorage basin on ground motions from the robust aftershock sequence. The USGS loss estimation tool PAGER issued a green alert for fatalities and an orange alert for economic losses, in accord with the observed impacts from the mainshock. About 700 people provided Did You Feel It (DYFI) reports, and the maximum reported shaking intensity was MMI VIII. PGAs in the Anchorage area were generally higher than 0.3 g, and PGVs were on the order of 30 cm/s. As of the end of January 2019, there were >350 magnitude 3 or larger earthquakes, and seven magnitude 5 or larger aftershocks. The aftershock forecasts have been updated multiple times and have been well received by the public and emergency managers. A team of USGS ground failure experts visited the impacted area, along with local geologists and engineers, to map ground failure (liquefaction and landsliding – no surface rupture occurred) and evaluate the performance of the new, rapid ground failure forecasting products. In our presentation, we will summarize the earthquake, results of the new USGS products, and lessons learned during our response to this earthquake.

Presenting Author: Keith L. Knudsen

Authors