Earthquakes in Alaska

The Earth's most active seismic belt is the circum-Pacific belt, which lies between Alaska and the Aleutian Islands. Six percent of large, shallow earthquakes are in the Alaskan region and more than 80% of the planet's tremors occur in the circum-Pacific belt.

The Great Alaskan Earthquake, 1964
Of all the earthquakes in Alaska, the biggest was The Great Alaskan earthquake, also known as the Good Friday earthquake, because it occurred on Good Friday, 27th March, 1964, at 5:36 PM local time and struck Prince William Sound with a magnitude of 9.2 Mw (moment magnitude). Its epicenter was located between Valdez and Anchorage, close to Prince William Sound and lasted anywhere between 3 to 5 minutes.

Coastal Alaska is located on a fault zone, which means that it is the meeting place of the Pacific plate and the North American plate. The earthquake occurred on a thrust fault, as the Pacific plate slipped underneath the North American plate. The slip of the Pacific plate took place nearly 16 miles underground, resulting in the earthquake. This slip caused the process of liquefaction, where ground clay turns into liquid and becomes unstable. As the Pacific plate plunged under the lighter continental crust, it pushed up portions of the ocean crust, causing volcanic eruptions with the magma rising to the ocean's surface in periodic eruptions.

Destruction in Anchorage
Anchorage is located 120 km northwest of the epicenter of the earthquake. It was most hit and damaged by this earthquake. The process of liquefaction caused rock slides and avalanches. Turnagain Heights was badly hit, as parts of this city, which is built on soft sandy clay buffs, collapsed during the strong ground motion. The property damage was immense, costing more than $311 million then. More than 75 houses in this place were destroyed due to the avalanche. Several schools collapsed. Fortunately, schools were closed due to the Good Friday holiday, else the human loss would have been abysmally high. At the Anchorage International Airport, the 68 foot tall concrete tower toppled over, killing the air traffic controller. Telephone, electrical service, water, sewer and gas lines were completely destroyed.

Destruction in Valdez
The Valdez port, which is located 120 miles east of Anchorage was completely destroyed by a giant harbor wave, killing 28 people on the dockyard. Many houses and commercial buildings were gutted down due to rising tides, that flooded many broad sections of Valdez. Many major Alaskan ports of Seward, Kodiak and Whittier along with coastal towns of Kodiak Island and Kenai Peninsula were destroyed by the great Alaskan earthquake.

Tsunamis
The earthquake resulted in the generation of tsunamis that added to the huge human and infrastructure losses. The Alaska-Aleutian mega thrust zone's co-seismic crustal movements produced vertical sea floor displacements, resulting in gigantic waves that crushed most of coastal Alaska, U.S. West Coast and British Columbia in Canada. Valdez (Shoup Bay) was hit by the largest wave measuring up to 67 meters in height. The tsunami generated due to the earthquake, reached the Alaskan coastal communities within minutes with an estimated speed of 400 miles per hour, making it difficult for help to reach in time, which caused disastrous losses. The tsunami traveled with great speed across the Pacific as far as the Hawaiian Islands causing extensive property damage.

Damage Control
The great Alaskan earthquake and its aftermath, highlighted the need to monitor the highly active seismic circum-Pacific belt. The West Coast & Alaska Tsunami Warning Center (WC&ATWC) was established in Palmer and its prime purpose is to sound earthquake and tsunami warnings for Alaska, British Columbia in Canada, California, Oregon and Washington. It also provides warnings to the general local public, national and international media agencies and the State and Federal disaster preparedness agencies.

The great Alaskan earthquake of 1964 was the largest earthquake ever recorded in North America in terms of magnitude, but was fortunate in terms of human life losses as Alaska is not densely populated. The Project on National Security Reform (PNSR) successfully coordinated federal and state agencies, to ensure speedy relief and recovery efforts, minimizing economic and human impact of the damage.