Deformation in the August 2018 Mw 6.4 Kaktovik (North Slope), Alaska Earthquake

Date: 4/24/2019

Time: 11:00 AM

Room: Pike

On August 12, 2018, a M=6.4 earthquake ruptured a roughly ESE-WNW-striking fault in the Sadlerochit Mountains on Alaska’s North Slope, ~90 km southwest of the nearest settlement of Kaktovik. The earthquake caused no injuries or damage due to its remote location, but it was the largest ever recorded on the North Slope and demonstrated that moderate to large earthquakes can and do occur in this corner of Alaska despite its distance from the effective Pacific-North American plate boundary (e.g. the Alaska-Aleutian subduction zone and Denali Fault) and comparatively low strain rate. Although no GPS stations were close enough to the earthquake to record substantial coseismic displacements, the earthquake’s location in sparsely vegetated terrain meant that the Sentinel-1 satellite provided excellent InSAR coverage of the coseismic displacement field (perhaps uncommon for Alaska earthquakes) on both ascending and descending tracks. These data suggested that the earthquake occurred on or near the Sadlerochit Mountains Fault, which runs west to east through the middle of this local mountain range. We invert the ascending and descending data (after applying adaptive downsampling) for coseismic displacements on a best-fit fault plane. The best-fitting fault plane appears to be slightly nonplanar and the InSAR data suggest mostly right-lateral slip with a slight normal component, consistent with the USGS focal mechanism. The geodetic moment is equivalent to Mw=6.4, consistent with the seismological estimate. Comparison of the InSAR pattern with aftershock locations suggests that 3D structure may substantially affect seismic travel times in this part of Alaska, making the Transportable Array and the coverage it provides all the more valuable in this region.

Presenting Author: Chris Rollins

Authors