Science & Technology



What makes an earthquake deadly? These are the things that matter

Corinne Purtill, Los Angeles Times on

Published in Science & Technology News

The biggest earthquake to hit the U.S. since the 1960s was an 8.2 temblor near the Alaskan Peninsula on July 28, 2021.

If you are struggling to recall the horrifying details, it's because there weren't any. No one was killed or injured in the Chignik earthquake, the seventh-largest in U.S. history. Not a single building fell. A post-quake inspection of Perryville, the closest town to the epicenter, revealed nothing more troubling than a few drywall cracks.

There will be no such sighs of relief in the areas devastated by the magnitude 7.8 earthquake that struck southern Turkey early Monday. The quake left more than 4,000 people dead, uncounted more injured and tens of thousands homeless as buildings collapsed around them.

Magnitude alone does not determine the full extent of an earthquake's damage. The amount of death and destruction any individual quake brings depends on multiple factors, each of which can make the difference between life and death for those on the ground.

Location, location, location

In the simplest and most obvious terms, the closer an earthquake is to a human settlement, the more damage it wreaks.


"It's kind of the real estate thing: Location, location, location," said Susan Hough, a seismologist with the U.S. Geological Survey in Pasadena. "I mean, magnitude matters. If it's a [magnitude] 3 versus an 8, that [makes] a difference. ... But for the most part, the further you get away from the fault that's moving, the more the energy spreads out, and it just loses its really severe punch."

The Chignik earthquake erupted about 20 miles beneath the seafloor off the Alaska Peninsula. It was deep enough that its energy had mostly dissipated by the time it reached the closest human settlement of Perryville, a village roughly 65 miles away with a population of about 100 people.

The Turkey earthquake has no such luck of geography. Like California's San Andreas fault, the East Anatolian fault — the seam along which this earthquake ruptured — runs under heavily populated areas.

Even worse, Monday's quake occurred relatively close to the surface, which translates to much stronger shaking on the ground. The main quake erupted about 11 miles (18 kilometers) below the surface, and a major 7.5 aftershock was even shallower, at 6 miles (10 km).


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