Alaska Earthquake

On January 23, 2018 a 7.9 magnitude earthquake struck southeast of Kodiak Island in the Gulf of Alaska. According to the U.S. Geological Survey (USGS) this earthquake occurred as the result of strike slip faulting within the Pacific plate.

At the location of the earthquake, the Pacific plate is converging with the North America plate. The Pacific plate subducts beneath the North America plate at the Alaska-Aleutians Trench, about 90 km to the northwest of last week’s earthquake. The location and mechanism of the January 23rd earthquake are consistent with it occurring on a fault system within the Pacific plate before it subducts.

Subduction zones are plate tectonic boundaries where two plates converge, and one plate is thrust beneath the other. This process results in earthquakes and volcanoes. This earthquake hazards affects the area around the edges of the Pacific Ocean contains subduction zones. The largest earthquakes on Earth occur in these areas.

The approximately 2,500-mile-long Alaska/Aleutian subduction zone stretches from Russia to Alaska. Here, the Pacific Plate and the North American plate are moving towards one another at a rate of about 2-3 inches per year. The Pacific Plate is thinner and denser, so it is being thrust underneath the North American plate. This subduction zone has generated many large, devastating earthquakes, including the second largest earthquake ever recorded: the 9.2 magnitude Good Friday earthquake in 1964 that devastated Anchorage and other Alaskan towns and the resulting tsunami caused deaths as far away as California.

Large earthquakes are common in the Pacific-North America plate boundary region. In the last century alone, besides the 1964 9.2 magnitude earthquake, there have been 10 others with magnitudes over 7 that. have occurred near the Pacific-North America plate boundary region . Most of these have occurred on the subduction zone interface between the two plates, to the north and northwest of last week’s earthquake. This past weekend a series of light earthquakes struck Alaska, not at all uncommon in this region.

Also a series of light earthquakes (4.0-5.8 earthquakes) have struck southern California. A light earthquake occurred on Thursday, January 25, 2018. The magnitude 4.0 event occurred 8 miles northeast of Trabuco Canyon, CA followed this past week by several light earthquakes (the type you do not easily notice). Finally, in Ferndale, CA there were two earthquakes yesterday, a 5.0 and 5.8 magnitude.



The magnitude of an earthquake is expressed in whole numbers and decimal fractions. For example, a magnitude 5.3 might be computed for a moderate earthquake, and a strong earthquake might be rated as magnitude 6.3. Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in the estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value. The ways to calculate have evolved over time.