Aftershock Analysis of the Mw 7 November 30, 2018 Anchorage Earthquake: Locations and Regional Moment Tensors

Date: 4/26/2019

Time: 10:45 AM

Room: Cascade II

The magnitude 7 Anchorage earthquake occurred in the morning hours of November 30, 2018 and generated intense ground shaking resulting in significant damage to the private property and public infrastructure. It was followed by a vigorous aftershock sequence with nearly 7,000 aftershocks reported through the end of December, 2018. Dozens of aftershocks were felt in the greater Anchorage area further increasing anxiety and keeping heightened public interest in the aftershock sequence updates. The Alaska Earthquake Center produced reviewed aftershock catalog with the magnitude of completeness of 1.6. When available, picks from temporary aftershock monitoring stations installed by the USGS in early December were used. This well recorded sequence provides additional constraints on the mainshock rupture process. The relocated hypocenters spread over a 25-km-long and 15-km-wide zone between 35-50 km depth confined to the subducting slab and indicate two aftershock clusters, a more diffuse shallow-dipping southern cluster and a more clearly-defined and steeply dipping northern cluster. However, regional moment tensor solutions for the aftershocks do not exhibit significant variability and, on average, agree well with the mainshock focal plane parameters, thus not necessarily supporting a multi-plane rupture. We use long-period regional seismic waveforms to estimate a point-source moment tensor for the mainshock. We grid search over the moment tensor space (double couple vs full moment tensor) and a range of depths. This presentation will address the M7 source geometry and rupture characteristics through the aftershock relocation analysis combined with the detailed investigations of the moment tensors.

Presenting Author: Natalia Ruppert

Authors