What are low-frequency vibrations?

Low-frequency vibrations are like the gentle shaking you feel when a big truck goes by, but much slower and softer.

Imagine you're sitting on a swing. When you pump your legs fast, you go high up and down quickly, that’s like a high-frequency vibration. But if someone gives you a little push every few seconds, you slowly rock back and forth, that's a low-frequency vibration. It doesn’t shake you hard, but it keeps moving you gently.

Sometimes, deep under the ground, things like mountains or big rocks can move very slowly, almost like they're taking deep breaths. These slow shakes are also low-frequency vibrations, and scientists listen to them like we listen to a heartbeat.

You might not feel them right away, but if you stand still for a while, you might notice your feet moving ever so slightly, just like how the earth feels when it’s sleepy and moving slowly.