Alaska Earthquake: A recent seismic event measuring 4.6 on the Richter scale shook Eagle River A significant earthquake happened in Alaskan Peninsula, Alaska’s seismic events shape the region’s landscape so what happend here is in jolted Eagle River at 6:47 a.m. this morning, an earthquake mild to moderate tremors to powerful quakes reaching magnitudes of 8 or 9 causing residents in Eagle River, Anchorage, and the Mat-Su Valley to abruptly awaken. Reports indicate that the experienced shaking ranged from mild to moderate intensity, with observations coming in from various locations, including Eagle River, Anchorage, Chujak, Wasilla, and the Kenai Peninsula in the south, as well as Taal in the north of Kitner. This seismic event shares similarities with the 2018 Anchorage earthquake, which had a magnitude of 7.1, as both were triggered by normal faulting resulting from the subduction of the Pacific Plate beneath Alaska.
In comparison to the 2018 Anchorage earthquake, today’s earthquake released significantly less energy. The 2018 earthquake released energy that was 1000 times greater than the earthquake this morning. However, during the 2018 event, there were limited seismometers capable of accurately measuring strong tremors in the area, which hindered the availability of precise location data in the hardest-hit areas between Mat-Su and Eagle River. Following the 2018 earthquake, efforts were made to strengthen monitoring capabilities.
Through a collaboration between the Alaska Earthquake Center at the University of Alaska Fairbanks (UAF) and the UAA Earthquake Department, seven new seismometers were deployed in the Mat-Su and Eagle Rivers . Additionally, two instruments capable of measuring vibrational strength were installed in Bethel. These enhancements now enable the calculation of ground acceleration and peak ground motion in these areas. Among the sensors, the ER02 sensor at Fire Station 11 in Eagle River recorded the strongest shaking during today’s event, with a peak ground acceleration of 14.64% of the acceleration due to gravity. Although this acceleration is considered moderate, it would have caused noticeable tremors for firefighters and residents in the vicinity.
In terms of strength, today’s earthquake is estimated to be approximately three to five times weaker than the 2018 Anchorage earthquake. The estimations for the 2018 earthquake were based on limited data due to the absence of sufficient strong-motion seismometers during that time. However, the significance of today’s event lies in its ability to provide measured values rather than relying solely on estimates. This newfound knowledge contributes to a better understanding of the relative ground shaking patterns in different regions. Consequently, this information can be utilized to improve the structural engineering of buildings, homes, and bridges, making them more resilient to future earthquakes.
In a separate incident on Sunday morning, a magnitude 7.2 earthquake struck the Alaska Peninsula, according to the United States Geological Survey (USGS). Initially, a tsunami warning was issued for southern Alaska and the coastal areas near the Alaska Peninsula. However, the U.S. tsunami warning system later retracted the warnings. The USGS revised the earthquake’s magnitude from the initial report of 7.4 to 7.2, and the depth was adjusted to 32.6 kilometers (20.3 miles) from the previously reported 9.3 kilometers.
Fortunately, there have been no immediate reports of damage or injuries, although some individuals shared videos on Twitter showing tsunami sirens sounding and strong shaking.
The propensity for seismic activity in Alaska can be attributed to the movement of tectonic plates, which shape the region’s topography, impact its rivers and glaciers, and even influence its climate zones. The Pacific Plate, which underlies the Pacific Ocean, is one of several tectonic plates composing the Earth’s crust. Each year, the Pacific Plate gradually moves a few inches towards Alaska, which is considered part of the North American Plate. The convergence of these plates leads to the subduction of the denser oceanic rocks beneath the less dense continental rocks, a process known as subduction.
Earthquakes occurring in subduction zones are characterized by the descent of the Pacific Plate to depths exceeding 200 kilometers. In Alaska, the largest earthquakes, reaching magnitudes of 8 or even 9, primarily occur in the shallow regions of the subduction zone where the crust of the Pacific Plate interacts with the overlying rocks, causing them to stick and slip. Notable examples of such earthquakes include the 1964 Good Friday earthquake, which had a magnitude of 9.2, and the 1965 Rat Islands earthquake, which registered at 8.7. These events rank as the second and eighth largest earthquakes ever recorded worldwide, respectively.
Southeast Alaska experiences distinct tectonic activity driven by the movement of the Pacific Plate. As the plate moves northwestward, it interacts with Alaska and British Columbia. Unlike subduction zones, the faults associated with this movement primarily exhibit lateral motion, with different tectonic plates present on either side. The resulting earthquakes are relatively shallow and occur within the Earth’s crust. This well-established fault system has been active for millions of years, generating numerous earthquakes throughout its history, some of which reached magnitudes of 8 or higher. The 2013 Queen Charlotte Fault earthquake, with a magnitude of 7.5, serves as an example of such an earthquake.
Additionally, the northwestward motion of the Pacific Plate exerts significant force on Alaska, compressing the land in a north-south direction and causing a shearing effect or lateral movement in southern Alaska. Numerous fault systems in Alaska accommodate this compression and shearing, resulting in a variety of seismic events. While the strength of these faults and our understanding of them diminishes towards the north, the impact of compression extends into the Arctic Ocean. Notable examples of earthquakes caused by this compressional force include the 2002 Denali Fault earthquake with a magnitude of 7.9 and the 1958 Husillah earthquake with a magnitude of 7.3. The Minto Flat seismic area also experiences high levels of seismicity due to this force.
In addition to mainshock-aftershock sequences, Alaska can also experience earthquake swarms, which involve a series of earthquakes. The exact cause of these swarms remains uncertain, but they occur throughout the state and vary in magnitude, number, and duration. In 2014, a swarm near Noatak rattled residents with five earthquakes ranging from magnitudes 5.3 to 5.7, spread over two months. Similarly, in 2015, St. George Island experienced a swarm that disrupted its typically calm environment. In 2018, a swarm in the eastern Brooks Range accounted for over 2,000 of the record-breaking 55,000 earthquakes reported in Alaska that year.
Alaska witnesses a significant number of earthquakes, with the Alaska Earthquake Center detecting an earthquake on average every fifteen minutes. In 2018, Alaska reported over 54,000 earthquakes, marking an all-time
high. As the monitoring network continues to evolve, more earthquakes are detected due to the increased capability to identify smaller seismic events across a larger geographical area. The subduction zones in Alaska are responsible for generating large earthquakes, including three of the twelve largest earthquakes ever recorded. Earthquakes with magnitudes of 6 or 7 can occur in almost any part of Alaska.
Over the past five years, Alaska has experienced more than 220,000 earthquakes, with 26 of them registering magnitudes of 6 or higher, and three reaching magnitudes of 7 or higher. Remarkably, over three-quarters of all earthquakes in the United States with magnitudes larger than five occur in Alaska.
The Alaska Earthquake Center’s primary focus is to understand earthquake occurrences and characteristics, aiming to minimize the associated risks. The continuous monitoring of earthquakes provides valuable insights for predicting future events. Prompt reporting of earthquakes allows the public and emergency managers to assess potential impacts. By measuring ground shaking in various locations and even within structures, the potential consequences can be evaluated, enabling appropriate emergency responses. The extensive monitoring network, with stations located in cities, towns, and critical infrastructure spanning from southeastern Alaska to the Bering Strait, showcases the far-reaching effects of earthquake hazards and the commitment to minimizing risks for all Alaskans.
In addition to earthquakes, the Alaska Earthquake Center monitors a range of other seismic phenomena, including landslides, glaciers, volcanoes, and mine blasts.
The 1964 Alaska earthquake stands as a testament to the seismic activity in the region. With a moment magnitude of 9.2, it released at least twice the energy of the 1906 San Francisco earthquake. Although the loss of life was relatively low at 131, property damage was substantial due to the sparse population in the area. The earthquake caused an area of at least 46,442 square miles (120,000 square kilometers) to tilt, resulting in localized uplift of up to 82 feet (25 meters) to the east of a line extending northeast from Kodiak Island through the western part of Prince William Sound. Conversely, the land subsided by as much as 8 feet (2.5 meters) to the west. Coastal regions suffered extensive damage from submarine landslides and subsequent tsunamis. The impact of the tsunami reached as far as Crescent City, California. The occurrence of tens of thousands of aftershocks indicated that the faulting extended approximately 620 miles (1,000 kilometers) along the subduction zone of the North Pacific Plate.
