earthquake

An earthquake is the ground suddenly shaking because rock deep below has lurched. The Earth's outer shell is cracked into giant slabs that slowly push, pull, and grind against one another — colliding, pulling apart, or sliding past — and along the cracks between them, called faults, the rock often gets stuck, locked tight by friction while the slabs keep moving. Stress piles up for years or centuries, like a bent stick storing more and more spring, until the fault finally gives way and slips in an instant. That snap is the earthquake.

All that stored-up energy escapes as seismic waves — ripples that race outward through the rock in every direction, exactly the way ripples spread when you drop a stone in a pond. When they reach the surface they make the ground heave and roll, which is the shaking you feel. The scientists' magnitude scale measures how much energy a quake releases, and it climbs steeply: each step up of one number is about 32 times more energy, so a magnitude 7 is not a little bigger than a 6 — it's vastly more violent.

A common misconception is that the ground splits open and swallows people whole. It doesn't. Faults move along their length, and the real danger is almost always the shaking — buildings, bridges, and walls collapsing as the seismic waves rattle them. That's why a modest quake can be deadly where buildings are weak, yet a strong one barely harm anyone where they're built to sway and hold.