5 Facts About Earthquakes That Will Surprise You

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The ground under our feet feels permanent and still, but that’s mostly an illusion built from scale. These facts about earthquakes show that the planet is moving constantly — just usually too slowly or too faintly for us to notice.

1. Most earthquakes happen without anyone feeling them

Scientists estimate the Earth experiences somewhere between 1 and 1.5 million earthquakes every year, but the vast majority sit below magnitude 2.5 — too weak for a person to feel, only detectable by sensitive seismographs positioned around the globe. Only a small fraction ever approach magnitude 6, the point where structural damage typically starts becoming serious. That means, quite literally, some corner of the planet is probably trembling on a tiny scale right now.

2. “Silent” earthquakes can last for weeks

Not every shift between tectonic plates happens in a sudden jolt. So-called slow slip events release roughly the same amount of energy as a normal earthquake, but spread out over days or even weeks — gradually enough that nobody feels a thing at the surface. These events were only identified starting in the early 2000s, thanks to high-precision GPS networks capable of detecting ground movements of just a few millimeters, and they’re now studied as a possible clue for understanding how fault lines behave before a larger rupture.

3. The strongest earthquake ever recorded hit magnitude 9.5

On May 22, 1960, the coast of Chile was struck by the most powerful earthquake ever measured with modern instruments: magnitude 9.5 on the moment magnitude scale, caused by a rupture along more than 1,000 kilometers of fault line between the Nazca and South American plates. The quake triggered a tsunami that crossed the entire Pacific Ocean, causing deaths as far away as Japan — nearly 17,000 kilometers from the epicenter — roughly 22 hours after the initial shock.

4. Modern skyscrapers are designed to sway on purpose

Instead of trying to be rigid enough to resist movement entirely — which would eventually snap the structure — the most advanced earthquake-resistant buildings are engineered to move in a controlled way. Taipei 101 in Taiwan is one of the best-known examples: a 660-ton steel sphere suspended near the top of the tower acts as a tuned mass damper, swinging in the opposite direction of the building’s motion to cut vibration by up to 40% during strong winds or tremors.

5. Animals sometimes act strange before earthquakes — and science still isn’t sure exactly why

Reports of restless dogs, birds fleeing en masse, or fish behaving oddly minutes before a quake go back centuries across many cultures, and some recent studies using sensors on farm and wild animals recorded measurable behavioral shifts hours before tremors hit. The leading hypothesis is that certain animals may be picking up on microvibrations in the ground, changes in the air’s static electricity, or gases released from rocks under pressure — signals too faint for humans to register — but none of this is considered a reliable prediction method by seismologists yet.

6. A big enough earthquake can shorten Earth’s day

Massive earthquakes redistribute enough mass inside the planet to slightly change Earth’s moment of inertia — the same physics that makes a figure skater spin faster when pulling their arms in. The magnitude 9.1 earthquake that struck Japan in 2011 is estimated to have sped up Earth’s rotation enough to shorten the length of a day by roughly 1.8 microseconds — imperceptible in daily life, but measurable with the atomic clocks scientists use to track time.

Some places now get a few seconds of warning before the shaking starts

Earthquake early warning systems, deployed in places like Japan, Mexico, and increasingly the U.S. West Coast, work by detecting the fast, weaker P-waves that arrive first and sending an alert before the slower, more destructive S-waves reach populated areas. Because P-waves travel roughly twice as fast as S-waves, a network of sensors near the fault can sometimes give people tens of seconds of warning — enough time to step away from windows, stop a train, or pause surgery in an operating room — even though the system still can’t predict an earthquake before it actually starts.

Richter scale or moment magnitude: which one is actually used today

You’ve probably heard of the “Richter scale,” but seismologists barely use it anymore for large earthquakes. Created in 1935 by Charles Richter, it works well for moderate tremors recorded by a single type of local seismograph, but loses accuracy for very powerful earthquakes — an effect known as “scale saturation.” Starting in the 1970s, scientists shifted to the moment magnitude scale, which calculates released energy based on the size of the fault that ruptured, how far it slipped, and the rigidity of the rock involved — a far more accurate measure for major events like the 1960 Chile earthquake. So when a news report says “magnitude 7.2” today, it’s almost always referring to the moment magnitude scale, even though the popular term “Richter” still sticks around in everyday conversation.

Like volcanoes, earthquakes are a reminder that the planet’s crust is constantly rearranging itself — if this kind of restless geology interests you, check out our piece on facts about volcanoes too.