The 1 May 2017 British Columbia‐Alaska Earthquake Doublet and Implication for Complexity Near Southern End of Denali Fault System

Abstract

On 1 May 2017, two MW6.2 earthquakes occurred near the border of northwestern British Columbia and Alaska separated by about 2 hr in time. Despite their close distance (~10 km), the two events have different focal mechanisms, with the first featuring a reverse focal mechanism and the second strike slip. Both focal plane solutions are inconsistent with the nearby southeastern Denali fault system. To resolve their ruptured fault planes, we invert for the earthquake point source parameters and analyze rupture directivity via regional and teleseismic waveforms. We also model the near‐field GPS data and relocate the aftershocks to determine the fault planes. The results indicate that the first event ruptured updip along a steep SW‐dipping fault and the second event ruptured to the ESE along a left‐lateral fault. We infer that the earthquake doublet was related to the regional stress field and slip on the active Duke River fault. The involved faults are associated with transpression caused by the oblique collision of the Yakutat block.

Thermotectonic History of the Kluane Ranges and Evolution of the Eastern Denali Fault Zone in Southwestern Yukon, Canada

“…GPS measurements show ~5–10 mm/year of distributed horizontal shortening in the adjacent Kluane Ranges in response to ongoing Yakutat microplate collision (Marechal et al, ). Focal mechanisms of modern‐day earthquakes throughout the larger Kluane Ranges area indicate an active transpressional strain regime (He et al, ; Vallage et al, ).…”

Source parameters of the 2017Mw 6.2 Yukon earthquake doublet inferred from coseismic GPS and ALOS-2 deformation measurements

“…Three deformation components at GPS station TRTH were selected by He et al (2018) in their modelling. TRTH is located near the epicentre of eq.…”

“…MPSO has been successfully used in over 20 earthquakes, for example 2011 Figure 6. Spatial location of the best-fitting uniform slip faults inferred from the joint inversion of the InSAR and GPS data, and the GPS coseismic changes with the coseismic interferogram of T181 (20 160 731-20 170 730), where the GPS coseismic data were adopted from He et al (2018). The beach ball symbols are based on the fault solutions of the InSAR only data and a combination of the InSAR and GPS data, respectively.…”

“…(1) based on a preliminary earthquake report from the United States Geological Survey (USGS). He et al (2018) estimated the source characteristics of the earthquake doublet eqs (1) and (2) using seismic and GPS data and reported that they were reverse and strike-slip faulting processes, respectively. Vigorous ground motion triggered by the earthquake doublet were felt by residents at Whitehorse, the capital of the Yukon Territory, ∼130 km northeast of the epicentres.…”

“…1). Due to the close spatial relationship and consistent focal mechanisms with the local mechanical context of the Duke River fault, He et al (2018) (hereafter referred to as 'He2018') proposed that the two events were associated with the reactivation of the Duke Rive fault. Tectonically, the local tectonic activities in the region are driven by the plate collision between the North American plate and the Pacific plate (Christeson et al 2010).…”