M5.9 earthquake hits Southern Alaska at intermediate depth, U.S.

m5-9-earthquake-southern-alaska-december-22-2021

A strong earthquake registered by the USGS as M5.9 hit Southern Alaska at 22:42 UTC (13:42 LT) on December 22, 2021. The agency is reporting a depth of 152.6 km (94.8 miles). The EMSC is reporting M5.9 at a depth of 146 km (90.7 miles).

The epicenter was located about 62 km (38 miles) E of Port Alsworth (population 159) and 217 km (135 miles) SW of Anchorage (population 298 695), Alaska.

There are about 4 000 people living within 100 km (62 miles).

227 000 people are estimated to have felt light shaking.

The USGS issued a Green alert for shaking-related fatalities and economic losses. There is a low likelihood of casualties and damage.

Overall, the population in this region resides in structures that are resistant to earthquake shaking, though vulnerable structures exist. The predominant vulnerable building types are unreinforced brick masonry and reinforced masonry construction.

Image credit: TW/SAM, Goolge

Residents are advised to be aware of the possibility of aftershocks, especially when in or around vulnerable structures such as unreinforced masonry buildings.

This earthquake could be part of a sequence that may have larger and potentially damaging earthquakes in the future.

The USGS estimates the chance of more aftershocks as follows
(within the next 1 week until 23:40 UTC on December 28):

  • The chance of an earthquake of magnitude 3 or higher is 96 %, and it is most likely that as few as 0 or as many as 360 such earthquakes may occur in the case that the sequence is re-invigorated by a larger aftershock.
  • The chance of an earthquake of magnitude 5 or higher is 26 %, and it is most likely that as few as 0 or as many as 4 such earthquakes may occur.
  • The chance of an earthquake of magnitude 6 or higher is 5 %, and it is most likely that as few as 0 or as many as 1 such earthquakes may occur.
  • The chance of an earthquake of magnitude 7 or higher is 1 in 200, such an earthquake is possible but with a low probability.

Regional seismicity

Featured image credit: TW/SAM, Google

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