Near Islands Aleutian Earthquake with MW = 7.8 on July 17, 2017: I. Extended Rupture along the Commander Block of the Aleutian Island Arc from Observations in Kamchatka

Abstract

The largest instrumentally recorded regional back-arc earthquake with MW = 7.8, MC = 8.2 occurred on July 17, 2017 on the Bering transform fault (the boundary between the Beringia minor lithospheric plate and the Komandorskii (Commander) block of the Aleutian island arc). This seismic event, called the Near Islands earthquake or Near Islands Aleutian earthquake, caused the ground to shake with intensity I = 5–6 on Bering Island and a small tsunami wave on the Near Islands. The specific aspects of the peculiarities of the pattern of seismicity of the northwestern segment of the Aleutian arc and the tectonic position of the Near Island Aleutian earthquake, the details of its prompt processing, macroseismic manifestations, analysis results of ground motion peak amplitudes, focal mechanisms, and earthquake source models are discussed. The coseismic displacements according to the GNSS data are presented. It is concluded that the source of the Near Islands Aleutian earthquake did not fill the seismic gap near the Commander Islands, and the possibility of the strongest earthquake hitting the northwestern part of the Aleutian arc remains.