Tsunami threat after huge 7.2 quake roars through Alaska

On the night of July 15, 2023, a significant 7.2 magnitude earthquake shook the offshore region of the Alaska Peninsula. Coming almost three years after the previous 7.8 magnitude Simeonof Earthquake, this seismic event occurred 50 miles south of Sand Point, and about 100 miles southeast of the earlier quake’s epicenter, with a depth of about 20 miles.

Authorities issued an immediate tsunami warning following the quake, which was downgraded to an advisory within an hour and eventually canceled before 1:00 a.m. Tsunami waves of up to half a foot were recorded in King Cove and Sand Point, and residents in multiple communities on the Alaska Peninsula and eastern Aleutian Islands reported experiencing ground shaking of moderate intensity.

It was noted by the Earthquake Center that this latest tremor occurred within the aftershock zone of the 7.8 magnitude event. Despite the fact that the aftershock activity from the larger quake had significantly decreased since its peak in the summer of 2022, the center had been observing heightened levels of seismic activity within the zone throughout 2023. Therefore, this 7.2 magnitude earthquake could be considered a late aftershock of the previous quake, with a source mechanism similar to the Simeonof event, pointing to a fault rupture along the Aleutian megathrust fault.

7.2 magnitude earthquake strikes offshore Alaska, brings Tsunami warning. Photo courtesy of Soham K from Pixabay.

Experts anticipate that this recent quake will trigger its own aftershock sequence, in line with the pattern observed with other moderate-sized earthquakes in the region. In fact, the largest aftershock so far, of 5.0 magnitude, took place just three minutes after the main quake.

Significantly, another major earthquake, of 8.2 magnitude, occurred on July 29, 2022, northeast of the Simeonof Earthquake epicenter, with its rupture propagating northeast, away from the 7.8 magnitude rupture zone.

This latest 7.2 magnitude earthquake represents another major event within a three-year span that has ruptured the subduction zone interface from the Shumagin Islands in the southwest to Kodiak Island in the northeast. This region, recognized as a seismic gap where no major earthquakes had recently occurred, has now been partially filled by this sequence of large seismic events.