A magnitude 6.5 earthquake off Alaska is the latest in a string of earthquakes rattling the Pacific Ring of Fire, the vast zone of tectonic activity stretching around the Pacific Ocean.
The earthquake struck early Sept. 17 about 101 miles west-southwest of Nikolski in Alaska's Aleutian Islands, according to the U.S. Geological Survey. It occurred at a depth of about 71 miles, and only a few people reported feeling the shaking.
The Alaska earthquake came amid a busy stretch of seismic activity across the Pacific,including earthquakes in and around California.
A magnitude 3.5 earthquake struck offshore of Northern California near Eureka on Sept. 16, according to the USGS. The earthquake occurred about 40 miles southwest of Eureka at a depth of roughly
12.5 miles. It was initially reported as magnitude 3.6 before being revised.
The Bay Area also saw a pair of smaller earthquakes in recent days, including a magnitude 3.4 earthquake near Brentwood and a magnitude 3.0 earthquake in the same general area.
What is the Ring of Fire? Is it more active than normal?
The Ring of Fireis not a single fault or one continuous zone of earthquakes. It is a roughly 25,000-mile horseshoe-shaped belt around the Pacific Ocean where several tectonic plates meet, creating a complex network of faults, trenches, and volcanoes.
Those plates are constantly moving, and the way they interact varies from one part of the Pacific to another. They can collide, pull apart, or slide past each other, building stress in Earth's crust that can eventually be released as an earthquake.
That makes the Ring of Fire one of the most seismically active regions on the planet. About 81% of the world's largest earthquakes occur along the circum-Pacific seismic belt, according to theU.S. Geological Survey.
Some of the strongest earthquakes occur at subduction zones, where one tectonic plate is forced beneath another. Those boundaries are particularly important around Alaska's Aleutian Islands, the Pacific Northwest, Japan, Indonesia, and other parts of the Pacific.
But does that mean the Ring of Fire is more active than normal right now?
Not necessarily. Earthquake activity naturally fluctuates, and scientists can see periods when earthquakes cluster in a particular region before activity returns to a more typical level. A burst of earthquakes over several days does not, by itself, indicate that the entire Ring of Fire has become more active or that a larger earthquake is imminent.
The recent earthquakes around the Pacific are occurring within a region that is already constantly shaped by tectonic movement. While some of the earthquakes may be part of localized sequences, there is no reason to assume that earthquakes occurring thousands of miles apart are connected simply because they fall within the Ring of Fire.
Why do earthquakes sometimes come in clusters?
Earthquakes don't happen at a perfectly steady rate.
Scientists regularly see periods when earthquakes become more frequent in a particular area, followed by quieter stretches.
Some clusters are aftershock sequences following a larger earthquake. Others can result from changes in stress within the Earth's crust or from other local geological processes. That can make a region appear unusually active over a period of hours or days even though the overall rate of earthquakes remains within the range scientists expect.
And because the Ring of Fire covers such a huge area, earthquakes can occur in several countries or states within a short period without being part of the same sequence.
An earthquake in the Aleutian Islands, for example, does not automatically trigger an earthquake in California simply because both locations are part of the Ring of Fire.
Does more activity mean a major earthquake is coming?
Not necessarily.
The USGS says temporary increases or decreases in earthquake activity are part of the normal variation in seismicity. Scientists cannot use a short-term increase in earthquakes to reliably predict when or where a major earthquake will occur.
How California's earthquake landscape is different?
California is part of the Pacific Ring of Fire, but the tectonic forces shaping the state are different from those responsible for many of the largest earthquakes elsewhere around the Pacific. Along much of California's plate boundary, the Pacific Plate is moving northwest past the North American Plate, with that movement accommodated by a sprawling network of faults rather than a single boundary where one plate is forced beneath another.
The San Andreas Fault is the most recognizable example of this boundary type. It is a strike-slip fault, meaning the two sides of the fault primarily move horizontally past each other as the Pacific Plate slides northwest relative to the North American Plate. That movement doesn't happen smoothly, however. Friction can cause sections of a fault to lock together while tectonic forces continue to build, eventually releasing the accumulated stress as an earthquake.
The San Andreas is only one part of California's complicated fault system. The Hayward, Calaveras, San Jacinto and Garlock faults, among others, also accommodate movement through different parts of the state, and scientists continue to study how stress is distributed across these interconnected fault zones.
That complexity also helps explain why an earthquake in California can have a very different geological origin from one occurring elsewhere along the Ring of Fire. While the entire Pacific basin is shaped by tectonic plate movement, the specific faults, plate boundaries, and geological processes vary considerably from one region to another. An earthquake in Alaska's Aleutian Islands, for example, does not necessarily connect to an earthquake along one of California's fault systems.
Brandi D. Addison covers weather across the nation as the Weather Connect reporter for the USA TODAY Network and contributes to Texas Connect coverage across the state. She can be reached at baddison@usatodayco.com. Follow her on Facebook here.
This article originally appeared on Palm Springs Desert Sun: The Ring of Fire is living up to its name. Here's why
