Maps: 7.8-Magnitude Earthquake Off Russia Prompts Brief Tsunami Advisory in Alaska

A major, 7.8-magnitude earthquake struck in the North Pacific Ocean on Friday, according to the United States Geological Survey. The earthquake prompted a brief tsunami advisory, the second-highest alert level, for some coastal portions of western Alaska, which was lifted about two hours later.

The temblor happened at 6:58 a.m. Kamchatka time about 80 miles east of Petropavlovsk-Kamchatsky, Russia, data from the agency shows.

Tsunamis are a series of long waves caused by a large and sudden displacement of water in the ocean, usually from a large earthquake on or below the ocean floor. Tsunamis radiate in all directions from the epicenter and can cause dangerous coastal flooding and powerful currents that can last for hours or days.

The tsunami advisory had been in place for parts of the Alaskan coast that were closest to the earthquake. Farther away, the Pacific Tsunami Warning Center in Honolulu said there was no threat to Hawaii. “Based on all available data, a destructive Pacific-wide tsunami is not expected,” it said.

In late July, the same region was hit by an 8.8-magnitude earthquake. That quake, one of the strongest ever recorded, set off tsunami waves that reached as far away as Hawaii and California.

Kamchatka Peninsula in Russia’s Far East is so known for its wilderness and lack of communication links that it has become a byword for “remote” in the country. Kamchatka is sparsely populated, with about 300,000 residents mostly concentrated in three big towns in the south of the peninsula, including Petropavlovsk-Kamchatsky.

Moving around Kamchatka is difficult: The peninsula has just a few hundred miles of paved roads, mostly around major towns, and there are no roads to cross the swampland separating it from the mainland.

Tremors are regularly reported in this peninsula dotted with volcanoes, some of which erupt every year, and it has become a popular destination for tourism in recent years, with travel companies offering camping, helicopter rides and off-road tours for visitors to see the volcanoes or admire the pristine forests and rivers.

As seismologists review available data, they may revise the earthquake’s reported magnitude. Additional information collected about the earthquake may also prompt U.S.G.S. scientists to update the shake-severity map.

Aftershocks can occur days, weeks or even years after the first earthquake. These events can be of equal or larger magnitude to the initial earthquake, and they can continue to affect already damaged locations.