2018 Alaska Islands earthquake ShakeMap3

On January 23, 2018, at 00:31 AKST, an

earthquake An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

occurred in the

Gulf of Alaska The Gulf of Alaska ( Tlingit: ''Yéil T'ooch’'') is an arm of the Pacific Ocean defined by the curve of the southern coast of Alaska, stretching from the Alaska Peninsula and Kodiak Island in the west to the Alexander Archipelago in the ...

near

Kodiak Island Kodiak Island (, ) is a large island on the south coast of the U.S. state of Alaska, separated from the Alaska mainland by the Shelikof Strait. The largest island in the Kodiak Archipelago, Kodiak Island is the second largest island in the Un ...

. The earthquake, measured at 7.9 on the scale, was approximately southeast of Kodiak and happened at a depth of . It was initially measured as a M 8.2 event, but later downgraded by the

United States Geological Survey The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on Mar ...

. The earthquake was felt throughout most of southern Alaska, including the major cities of

Anchorage Anchorage, officially the Municipality of Anchorage, is the most populous city in the U.S. state of Alaska. With a population of 291,247 at the 2020 census, it contains nearly 40 percent of the state's population. The Anchorage metropolita ...

and Fairbanks, and parts of neighboring

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

. The earthquake prompted

tsunami A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, ...

warnings and advisories for Alaska,

Washington Washington most commonly refers to: * George Washington (1732–1799), the first president of the United States * Washington (state), a state in the Pacific Northwest of the United States * Washington, D.C., the capital of the United States ** A ...

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

, and

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

. Residents in low-lying areas along the Gulf of Alaska and in British Columbia were evacuated to shelters and higher ground. The

Pacific Tsunami Warning Center The Pacific Tsunami Warning Center (PTWC), located on Ford Island, Hawaii, is one of two tsunami warning centers in the United States, covering Hawaii, Guam, American Samoa and the Northern Mariana Islands in the Pacific, as well as Puerto Ric ...

later cancelled most of the alerts within four hours of the earthquake, due to the apparent lack of tsunami. The highest recorded waves after the event measured at under above tide level on Kodiak Island.

Earthquake

According to the

, the earthquake occurred southeast of

Kodiak, Alaska Kodiak (Alutiiq language, Alutiiq: ) is the main city and one of seven communities on Kodiak Island in Kodiak Island Borough, Alaska, Kodiak Island Borough, Alaska. All commercial transportation between the island's communities and the outside ...

at 12:31 AM local time (AKST). Witnesses to the earthquake itself reported that it was very long in duration, feeling like a "slow roller," but it was not a violent earthquake despite its magnitude and mercalli intensity, as its epicentre was hundreds of kilometres offshore. This was corroborated by witnesses in Anchorage. There was no immediate damage reported. The earthquake woke people in

, from the epicenter, and was felt as far as Fairbanks to the northeast and

to the southeast. The earthquake's

S wave __NOTOC__ In seismology and other areas involving elastic waves, S waves, secondary waves, or shear waves (sometimes called elastic S waves) are a type of elastic wave and are one of the two main types of elastic body waves, so named because t ...

s arrived in Anchorage within one minute, and reached Fairbanks within three minutes. The earthquake was a

strike-slip In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

event that occurred within the Pacific plate. The

epicenter The epicenter (), epicentre, or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Determination The primary purpose of a ...

was to the south of the

Aleutian Trench The Aleutian Trench (or Aleutian Trough) is an oceanic trench along a convergent plate boundary which runs along the southern coastline of Alaska and the Aleutian islands. The trench extends for from a triple junction in the west with the Ula ...

, where the Pacific plate

subducts Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second pla ...

beneath the North American plate. The region has produced twelve large earthquakes since 1900, including several

megathrust earthquake Megathrust earthquakes occur at convergent plate boundaries, where one tectonic plate is forced underneath another. The earthquakes are caused by slip along the thrust fault that forms the contact between the two plates. These interplate earthq ...

Aftershocks

The first major

aftershock In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in Epicenter, the same area of the Mainshock, main shock, caused as the displaced Crust (geology), crust adjusts to the effects of the main shock. Large earthq ...

s occurred 20 minutes after the earthquake. The strongest aftershock measured 5.5 on the moment magnitude scale, while most measured 4–5. Within two days, the United States Geological Survey recorded over 50 aftershocks. More than 560 aftershocks have been recorded well into March.

Alerts and evacuations

Communities on Kodiak Island and other coastal areas on the Gulf of Alaska and

Cook Inlet Cook Inlet (; Sugpiaq language, Sugpiaq: ''Cungaaciq'') stretches from the Gulf of Alaska to Anchorage, Alaska, Anchorage in south-central Alaska. Cook Inlet branches into the Knik Arm and Turnagain Arm at its northern end, almost surrounding ...

were evacuated after warning sirens were activated. Hundreds gathered in local schools, which were opened as evacuation shelters, in Kodiak, Seward, and

Homer Homer (; , ; possibly born ) was an Ancient Greece, Ancient Greek poet who is credited as the author of the ''Iliad'' and the ''Odyssey'', two epic poems that are foundational works of ancient Greek literature. Despite doubts about his autho ...

. Evacuees seeking higher ground filled local roads and the parking lots of supermarkets, while locals reported large numbers of evacuees parking near a

wind farm A wind farm, also called a wind park or wind power plant, is a group of wind turbines in the same location used to produce electricity. Wind farms vary in size from a small number of turbines to several hundred wind turbines covering an exten ...

on Pillar Mountain near Kodiak. An unrelated power outage at the Alaska Earthquake Center in Fairbanks caused some alerts to be delayed, while its website was overwhelmed by the number of users. The

National Weather Service The National Weather Service (NWS) is an Government agency, agency of the Federal government of the United States, United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weathe ...

sent emergency alerts to cell phones in Alaska, reading, "Emergency Alert. Tsunami danger on the coast. Go to high ground or move inland." The National Weather Service and

initially issued a tsunami watch for Hawaii and the entire West Coast, but cancelled them after less than two hours. In the

San Francisco Bay Area The San Francisco Bay Area, commonly known as the Bay Area, is a List of regions of California, region of California surrounding and including San Francisco Bay, and anchored by the cities of Oakland, San Francisco, and San Jose, California, S ...

, residents within three blocks of the Pacific coast and five blocks of the

San Francisco Bay San Francisco Bay (Chochenyo language, Chochenyo: 'ommu) is a large tidal estuary in the United States, U.S. state of California, and gives its name to the San Francisco Bay Area. It is dominated by the cities of San Francisco, California, San ...

were warned by the city's Department of Emergency Management to be ready for evacuation. Some aspects of the warning systems in place were delayed or failed to issue a warning at all, prompting multiple reviews of the warning infrastructure.

References

External links

* {{DEFAULTSORT:Gulf of Alaska earthquake, 2018 2018 earthquakes 2018 in Alaska Earthquakes in Alaska January 2018 in the United States 2018 tsunamis

Earthquake

Aftershocks

Alerts and evacuations

See also

References

External links