The Alaska Earthquake Centre recorded a Magnitude 7.2 Earthquake at a depth of 32.6 km, to the south of the Alaska Peninsula, slightly before 10.50 pm on Saturday 15 July 2023, Alaskan Standard Time (slightly before 6.50 am on Sunday 16 July GMT). There are no reports of any damage or casualties associated with this event, but people have reported feeling it as far away as Anchorage, and the United States Geological Survey has issued a tsunami warning, due to the magnitude and shallow nature of the event.
Alaska lies on the North American Plate, with the Pacific Plate underlying the ocean to the south. The Aleutian Trench runs along much of the south coast of Alaska, with the Pacific Plate being subducted beneath this and passing under Alaska as it sinks into the Earth. Off the coast of southeast Alaska the Pacific and North American Plates pass one-another horizontally, with the Pacific Plate moving northward and the North American to the south (a transform plate margin). This is not a smooth process, and the plates frequently stick together, then break apart as the pressure builds up, causing Earthquakes.
Earthquakes along subductive margins are particularly prone to causing tsunamis, since these often occur when the overlying plate has stuck to the underlying plate, being pulled out of shape by its movement.. Eventually the pressure builds up to far and the overlying plate snaps back, causing an Earthquake and a tsunami.
Witness accounts of quakes can help geologists to understand these events and the rock structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) you can report it to the United States Geological Survey here.
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