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Large earthquakes can create many hazards such as liquefaction and landslides. The USGS has added near-real-time estimates of such ground failures for this earthquake event. This is the first major earthquake in the United States for which this product is available. The models indicate that liquefaction and landsliding have likely occurred and may be responsible for damage to infrastructure, with liquefaction potentially being the larger issue.
Because this earthquake is so widespread, inspections are taking place across the state. AFTERSHOCKS AND SETTLING ARE EXPANDING THE DAMAGE TO DRIVING LANES. DOT&PF is advising the public that detours are slow, and to please plan for additional time when traveling the area. Construction crews are actively repairing slope failures, however, the area is still dynamic and repairs will take time. DOT&PF is advising the public that detours are slow, and to please plan for additional time when traveling the area. Construction crews are actively repairing slope failures, however repairs will take time.
Anchorage earthquake
DOT&PF has documented over 40 damage sites on transportation infrastructure. DOT&PF has documented approximately 50 sites of potential damage sites. Northbound Briggs Bridge on Eagle River Loop Road is now closed. If a bridge is determined to be unsafe to travel over , we will close the area to travel. If the bridge is determined to be structurally sound, it will remain open.
Three hours after the initial tsunami advisory was issued, NOAA canceled it. We reported over 220,000 earthquakes in Alaska over the last five years. Twenty-six of those had magnitudes of 6 or greater, and three had magnitudes of at least 7. Seventy-five percent of all earthquakes in the United States with magnitudes larger than five happen in Alaska. The subduction zone produces very large earthquakes—as large as anywhere in the world—including three of the twelve largest earthquakes ever recorded. Magnitude six and seven earthquakes can nearly happen anywhere in Alaska.
Updated tsunami inundation maps for Homer and Seldovia, Alaska
By measuring the shaking across the region, and even in buildings, we are able to assess the potential impacts and determine what type of emergency response is likely to be most effective. Subduction zone earthquakes follow the descent of the Pacific plate down to 200 km or more. Alaska’s largest earthquakes, exceeding magnitude 8 and even 9, occur primarily in the shallow part of the subduction zone, where the crust of the Pacific Plate sticks and slips past the overlying crust. From the dramatic Southeast coast to the heights of the Alaska Range and the volcanic islands of the Aleutians, earthquakes build the landscapes that drive Alaska’s rivers, glaciers, and even climate zones.
Other than that, we have had some incidental reports of damage to things like appliances and homes and other things. At the same time, a Tsunami Watch was issued for California, Oregon, and Washington. Ultimately, a small tsunami surge, less than one foot deep, was observed in Kodiak and smaller water-level increases occurred in other Alaskan coastal communities. A water-level rise of a few inches was detected four and a half hours later in Arena Cove, California.
TRANSPORTATION and PUBLIC FACILITIES
In the Anchorage community of Eagle River, at least one home collapsed during the earthquake. One man in the home, whose spouse was at work, was able to escape with several pets. DOT&PF Maintenance and Construction crews are now actively working the eight major damage sites. Aftershocks are continuing to contribute to settling and additional cracking. After this earthquake, we will need to make repairs to some bridges to ensure they are safe for the traveling public.
Similarly, in Seward, students from other schools were evacuated to Seward High School. Watchstanders, or scientists who monitor earthquakes, get computer generated alarms indicating potential danger from quakes, but last Friday they didn’t need that. At the time of the tremblor, however, Spencer said they were in a café across the street. He said power went out almost immediately after the earthquake began.
Assessments on critical state facilities have been completed or are scheduled for completion in the next 2 days. Since the 1964 Alaskan earthquake, a magnitude 9.2, Alaska has had 144 earthquakes above magnitude 6. Because scientists were looking at potential sources of landslides, they had to look at a worst-case scenario of the furthest distance from a possible tsunami and the time it would take to reach impacted areas. When no waves were observed hitting tide gauges in those areas, the center canceled the warning.
This is a different mechanism than megathrust faults in the region, which do occur on the plate boundary itself. This faulting in the Pacific Plate is caused by downward bending while the plate is being forced under Alaska. Southern Alaska lies at the eastern end of the Aleutian Trench, where the Pacific Plate is subducting beneath the North American Plate. Near Anchorage, the plates are converging at a rate of 57 mm per year. The region has experienced severe earthquakes in the past, including several megathrust earthquakes. The 1964 earthquake, with a magnitude of 9.2, was the largest earthquake in American history and the second largest to ever be recorded anywhere in the world.
In addition, Matanuska Electric Association reported that 46,000 customers were left without electricity immediately after the earthquake. The earthquake had a magnitude of 7.1 on the moment magnitude scale using a centroid moment tensor inversion of the W-phase. The focal mechanism shows that the earthquake was a result of normal faulting.
The bulk of the Alaska Earthquake Center catalog is above magnitude 1.5. The Alaska Volcano Observatory plays an important role in tracking the smaller earthquakes common in volcanic areas. Alaska Volcano Observatory to track all notable seismic activity in the state. The Earthquake Center addresses large earthquakes and their societal impacts, while the Volcano Observatory focuses on the smaller earthquakes that can occur in large numbers near volcanoes.
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