The Simeonof cluster is named for Simeonof Island, in the Shumagin
Islands group of the Aleutian Islands, southern Alaska, U.S.A. It
includes the magnitude 7.8 Mw and 7.6 Mw Simeonof earthquakes on July 22
and October 19, 2020, and the 7.2 Mw earthquake on July 16, 2025. All
events have depth control, primarily from arrival time observations at
stations at near-epicentral and local distances and many of the larger
events also have depth control from teleseismic depth phases. There are
many cases with both types of constraint in which the agreement is very
good. The ability to calibrate the location of this cluster depends
heavily on including deeper events (to ~60 km) that provide raypaths to
the north and northwest, balancing the raypaths to events offshore to
the southeast.
