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Chile is on a hotspot of sorts for earthquake activity, according to a Live Science report. And so the 8.8-magnitude temblor that shook the region overnight was not a surprise, historically speaking. Nor was it outside the realm of normal, scientists say, even though it comes on the heels of other major earthquakes.

One scientist, however, says that relative to the time period from the mid-1970s to the mid-1990s, Earth has been more active over the past 15 years or so. 

The Chilean earthquake, and the tsunami it spawned, originated on a hot spot known as a subduction zone, where one plate of Earth’s crust dives under another. It’s part of the active “Ring of Fire,” a zone of major crustal plate clashes that surround the Pacific Ocean.

“This particular subduction zone has produced very damaging earthquakes throughout is history,” said Randy Baldwin, a geophysicist with the U.S. Geological Survey.

The largest quake ever recorded, magnitude 9.5, occurred along the same fault zone in May 1960.

Even so, magnitude-8 earthquakes occur globally, on average, just once a year. Since magnitudes are given on a logarithmic scale, an 8.8-magnitude is much more intense than a magnitude 8, and so this event would be even rarer, said J. Ramón Arrowsmith, a geologist at Arizona State University.

“Relative to the 20-year period from the mid-1970s to the mid 1990s, the Earth has been more active over the past 15 or so years,” said Stephen S. Gao, a geophysicist at Missouri University of Science and Technology. “We still do not know the reason for this yet. Could simply be the natural temporal variation of the stress field in the earth’s lithosphere.” (The lithosphere is the outer solid part of the Earth.)

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