Here’s Why Alaska’s Magnitude 7.1 Quake Was So Big

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Andrew Follett Energy and Science Reporter
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An unusually powerful magnitude 7.1 earthquake was caused by tectonic plates colliding deep beneath Alaska Sunday morning, destroying four houses, damaging several roads and knocking out electricity.

The United States Geological Survey (USGS) said the earthquake’s epicenter was located 162 miles southwest of Anchorage, Alaska. The earthquake was the result of the Pacific tectonic plate colliding with and subducting beneath the North American tectonic plate. This causes rocks deep underground to deform and tremendous stress to build up, which can then be released by earthquakes. The same forces that caused the quake, for example, also created the Aleutian Islands.

In the region of the earthquake, the Pacific plate is slamming into the North America plate at a rate of 2.36 to 2.99 inches per year, which is very fast in geologic terms. Since 1900, this region has hosted twelve other earthquakes with magnitudes higher than 7.0.

The USGS classified the shaking as an intermediate-depth earthquake. Such quakes typically cause less damage than equally powerful earthquakes that occur at shallower depths, but intermediate-depth earthquakes can often be felt very far away from the epicenter.

No injuries or deaths were reported.

“Last night’s earthquake is significant because it was close enough to Alaska’s population centers,” Michael West, Alaska’s state seismologist, told reporters at the Associated Press. “This earthquake is of the style and type that we would expect in this area.”

The quake was widely felt across most of Alaska, but caused relatively little damage. Only four homes were destroyed due to gas leaks, which is remarkably little damage.

The subducting Pacific plate is responsible for the so-called “Ring of Fire,” where roughly 90 percent of the world’s earthquakes and 81 percent of the world’s largest earthquakes occur. The Ring of Fire is the direct result of collisions between the Pacific tectonic plate and other plates. It is the most geologically active area on Earth and is also home to 75 percent of the world’s active volcanoes.

A 1938 earthquake similar to Sunday’s generated a tsunami recorded as far south as Hawaii.

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