Major M7.8 earthquake hits near the coast of Alaska Peninsula, U.S. — tsunami warning issued
A very strong and shallow earthquake registered by the USGS as M7.8 hit near the coast of Alaska Peninsula, U.S. at 06:12 UTC on July 22, 2020 (19:12 LT, July 21). The agency is reporting a depth of 28 km (17.4 miles). EMSC registered it as M7.8 at a depth of 30 km (18.6 miles).
The epicenter was located 98.9 km (61.3 miles) SSE of Perryville and 845.9 km (524.5 miles) SSW of Anchorage, Alaska.
There are just a few people living within 100 km (6.2 miles).
1 000 people are estimated to have felt moderate shaking and 1 000 light.
Based on all available data, hazardous tsunami waves are forecast for some coasts, PTWC said at 06:55 UTC, adding that it’s still waiting for more data to confirm.
A Tsunami Warning is in effect for:
SOUTH ALASKA AND THE ALASKA PENINSULA, Pacific coasts from Kennedy Entrance, Alaska (64 km / 40 miles SW of Homer) to Unimak Pass, Alaska (128 km / 80 miles NE of Unalaska).
ALEUTIAN ISLANDS, Unimak Pass, Alaska (128 km / 80 miles NE of Unalaska) to Samalga Pass, Alaska (48 km / 30 miles SW of Nikolski).
A Tsunami Advisory is in effect for:
SOUTH ALASKA AND THE ALASKA PENINSULA, Pacific coasts from Cape Suckling, Alaska (120 km / 75 miles SE of Cordova) to Kennedy Entrance, Alaska (64 km / 40 miles SW of Homer).
ALEUTIAN ISLANDS, Samalga Pass, Alaska (48 km / 30 miles SW of Nikolski) to Amchitka Pass, Alaska (201 km / 125 miles W of Adak) including the Pribilof Islands.
Actions to protect human life and property will vary within tsunami warning areas and within tsunami advisory areas.
If you are in a tsunami warning area:
* Evacuate inland or to higher ground above and beyond designated tsunami hazard zones or move to an upper floor of a multi-story building depending on your situation.
If you are in a tsunami warning or advisory area:
* Move out of the water, off the beach, and away from harbors, marinas, breakwaters, bays and inlets.
* Be alert to and follow instructions from your local emergency officials because they may have more detailed or specific information for your location.
* If you feel a strong earthquake or extended ground rolling take immediate protective actions such as moving inland and/or uphill preferably by foot.
* Boat operators, where time and conditions permit, move your boat out to sea to a depth of at least 55 m (180 feet).
* If at sea avoid entering shallow water, harbors, marinas, bays, and inlets to avoid floating and submerged debris and strong currents.
* Do not go to the shore to observe the tsunami.
* Do not return to the coast until local emergency officials indicate it is safe to do so.
Tsunami waves are forecast to be less than 0.3 m (1 foot) above the tide level for the coasts of Chuuk, Guam, Hawaii, Howland and Baker, Japan, Johnston Atoll, Kiribati, Kosrae, Marshall Islands, Mexico, Midway Island, Northern Marianas, Northwestern Hawaiian Islands, Palau, Palmyra Island, Pohnpei, Russia, Wake Island, and Yap.
The Tsunami Warning was canceled for the coastal areas of South Alaska and the Alaska Peninsula and the Aleutian Islands at 10:23 UTC.
“A tsunami was generated by this event, but no longer poses a threat,” NTWC said. “Some areas may continue to see small sea level changes. The determination to re-occupy hazard zones must be made by local officials.”
Image credit: TW/SAM, Google
Over the next 1 week, there is a 4% chance of one or more aftershocks that are larger than magnitude 7.8, according to the USGS forecast.
It is likely that there will be smaller earthquakes over the next 1 week, with 140 to 13 000 magnitude 3 or higher aftershocks.
Magnitude 3 and above are large enough to be felt near the epicenter. The number of aftershocks will drop off over time, but a large aftershock can increase the numbers again, temporarily.
The USGS estimates the chance of more aftershocks as follows: Within the next 1 week until July 29, 2020 at 07:10 UTC:
- The chance of an earthquake of magnitude 3 or higher is > 99%, and it is most likely that as few as 140 or as many as 13 000 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 98%, and it is most likely that as few as 0 or as many as 130 such earthquakes may occur.
- The chance of an earthquake of magnitude 6 or higher is 68%, and it is most likely that as few as 0 or as many as 14 such earthquakes may occur.
- The chance of an earthquake of magnitude 7 or higher is 18%, and it is most likely that as few as 0 or as many as 3 such earthquakes may occur.
Estimated population exposure to earthquake 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.