July 2020 Alaska Peninsula earthquake

The shallow earthquake was the result of thrust faulting[1] on the Aleutian subduction zone[6] where the Pacific plate subducts underneath the North American plate, forming the Aleutian Trench and Arc. This convergent boundary is one of the most active in the world, and was the location of the M_w9.2 1964 Alaska earthquake; the largest recorded in North America, and the second largest in the world.[7] On average, the rate at which these plates converge is about 64 mm/year.[8] The earthquake struck east of the Shumagin Gap, a 125 mile-wide (200 km) seismic gap in the subduction zone which hasn't ruptured with a large quake for at least 100 years.[9] Previously, it was thought that the subducting plate in the Shumagin Gap was poorly coupled to the overriding crust, quietly slipping and preventing large quakes. However, research suggests that the seismic gap, contrary to speculation that it might be a relatively “safe” seismic zone in the arc, may pose a threat similar to that of the rest of the Aleutian subduction zone.[10]

The earthquake ruptured an area of about 120 mi × 60 mi (193 km × 97 km), equal to about 7,200 sq mi (19,000 km²). The estimated maximum slip along this fault surface was about 3 to 4 m (9.8 to 13.1 ft).[11] It was reportedly felt as far as Vancouver and Victoria, more than 1,500 miles (2,400 km) away.[12][13]

There have been no reports of severe damage or injuries.[14][15] Mild damage occurred in Sand Point with reports of damaged docks, cracked roads and cement.[16]

Within the first 5 hours proceeding the mainshock, there were 6 aftershocks at or above M 4.5, including a mb 6.1 occurring less than 4 minutes later.[22][23] One week later on July 28, another M_ww6.1 aftershock occurred west of the mainshock.[24][4]

On October 19, an M_ww 7.6 aftershock affected the same area, prompting tsunami warnings and advisories.[25] It is the largest aftershock of the sequence.