Craig, Alaska Earthquake: 01/05/13
Summary:
On January 5, 2013 a 7.5 magnitude earthquake occurred 71 miles southwest of Craig, Alaska. For a comparison, a 7.5 magnitude earthquake can release almost as much energy as detonating a million tons of TNT. This earthquake was generated by movement in the Queen Charlotte Fault; a transform fault. Here, the Pacific plate is moving northwest with respect to the North American plate. This earthquake was one of the largest earthquakes seen in this region in the past 60 years. Fortunately, very little damage was caused, amounting to items knocked off shelves in Craig. Approximately 150 aftershocks occurred in the following 24 hours from the event, however the majority of them were quite small and in the 2-3 magnitude range. Only ten aftershocks ranged above a magnitude 4, with one reaching a notable 5.1 magnitude. It is important to remember that for every unit of magnitude larger a shock is, it releases 31.6 times more energy and generates 10 times as much groundshaking. The event caused a rupture in the fault about 50 km and caused the plates to slip 7-8 meters.
About the Areas Affected
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Luckily most of the areas surrounding the queen charolette fault are sparsely populated and have a relatively sound infrastructure. The nearest town to the earthquake was Craig, Alaska, which has a total population of 1,201 people according to the 2010 census. It is the largest town on the Prince of Wales Island. There are about 600 housing units in Craig, Ak. 95% of which were constructed after 1950. These relatively new buildings were relatively insensitive to the moderate shaking caused during the Jan. 5th earthquake.
The biggest money makers in Craig, AK are commercial fishing, fish processing, and commercial timber. Craig also relies heavily on tourism and recreation, including sport fishing, bear hunting, camping, and canoeing, all of which attract non-Alaskans to the island town. The mean income is $20,176 per capita, and $45,298 per household4. Only 9.8% of Craig, Alaskans are below poverty.
After every large earthquake, USGS performs a "did you feel it" survey where participants living in regions surrounding the seismic event indicate whether or not they felt the shock waves which propogated from the earthquake focus. The results include population demographics of the surrounding region, and a rough accessment of the shaking intensity of the earthquake.
The biggest money makers in Craig, AK are commercial fishing, fish processing, and commercial timber. Craig also relies heavily on tourism and recreation, including sport fishing, bear hunting, camping, and canoeing, all of which attract non-Alaskans to the island town. The mean income is $20,176 per capita, and $45,298 per household4. Only 9.8% of Craig, Alaskans are below poverty.
After every large earthquake, USGS performs a "did you feel it" survey where participants living in regions surrounding the seismic event indicate whether or not they felt the shock waves which propogated from the earthquake focus. The results include population demographics of the surrounding region, and a rough accessment of the shaking intensity of the earthquake.
Seismic History of the Queen Charolette Fault
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Epicenters of earthquakes since 1900 (aeic, alaska.edu)
The queen Charolette fault has generated a number of noteable seismic events during the past 100 years. Although far from predictable, a large earthquake (M7+) generally occurs every 25 years. Earthquakes along the fault are usually a result of strike slip, or oblique strike slip motion. Some of the most interesting seismic events that have happened along this fault system are a magnitude 8.1 earthquake in 1949, and a magnitude 7.9 earthquake in 1958. The 1958 earthquake generated a landslide; nearly half of a mountainside slide into the ocean creating a tsunami which reportedly tossed boats over top of a 30 meter spit surrounding a harbor. Accompanying the January 5, 2013 earthquake, a small tsunami warning issued by the West Coast and Alaskan Tsunami Warning Center for Prince of Wales Island directly after the storm, but the largest wave surge recorded was barely 2.5 feet above sea level as no rockslide was generated like the 1958 earthquake.