Very strong M7.2 earthquake hits Alaska Peninsula, U.S. – Tsunami Advisory issued

A very strong earthquake registered by the USGS as M7.2 (downgraded from M7.4) hit near the coast of the Alaska Peninsula, U.S. at 06:48 UTC on July 16, 2023. The agency is reporting a depth of 32.6 km (20.2 miles). EMSC is reporting M7.4 at a depth of 10 km (6.2 miles).

The epicenter was located 98.7 km (61.4 miles) S of Sand Point (population 1 064) and 984 km (611 miles) SW of Anchorage (population 291 247), Alaska.

A Tsunami Advisory is in effect for South Alaska and the Alaska Peninsula, Pacific coasts from Chignik Bay to Unimak Pass, Alaska (128 km / 80 miles NE of Unalaska). For other U.S. and Canadian Pacific coasts in North America, there is no tsunami threat, NWS NTWC said.

If you are in a tsunami 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 Advisory update **

The Tsunami Advisory is canceled for the coastal areas of South Alaska and the Alaska Peninsula, NWS NTWC said at 10:47 UTC.

A tsunami was generated by this event, but no longer poses a threat. Some areas, however, may continue to see small sea level changes.

King Cove and Sand Point, Alaska recorded a maximum tsunami height of 15 cm (0.5 feet) at 11:18 UTC.

** End of Tsunami Advisory update **

2 000 people are estimated to have felt strong shaking, and 1 000 moderate.

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.

According to the USGS forecast, there is an 86% chance of one or more aftershocks that are larger than magnitude 5, which can be damaging, within the next week. There will likely be smaller aftershocks within the next week, with up to 3 300 M3 or higher aftershocks. M3 and higher aftershocks are large enough to be felt nearby. The number of aftershocks will decrease over time, but a large aftershock can temporarily increase the number of aftershocks.

This forecast applies to the area where the earthquake and aftershocks are already occurring.

Estimated population exposure to earthquake shaking

Regional seismicity

Featured image credit: TW/SAM, Google