Earthquakes Shake Buildings Differently - Why do earthquakes flatten some buildings and leave the one next door standing? Resonance. In this simulation we shook the same small city four times. Each test starts from a fresh scene, and the only thing we change is the frequency of the shaking, meaning how many times per second the ground moves back and forth. 🏢 0.91 Hz: the tallest tower collapses 🏢 1.25 Hz: the 8-floor building collapses 🏢 2.00 Hz: the 5-floor building collapses 🏢 3.33 Hz: the shortest building collapses Every building has a natural frequency, the rate it prefers to sway at. Tall buildings are heavy and flexible, so they sway slowly (low frequency). Short buildings are stiff, so they vibrate quickly (high frequency). Engineers use a rough rule of thumb: natural frequency ≈ 10 ÷ number of floors. When the ground shakes at a building's own frequency, each push lands at just the right moment, the swaying keeps growing, and the structure fails. The buildings that don't match barely react. Is this the same magnitude earthquake every time? In this simulation, yes. The shaking strength stays the same and only the frequency changes. That's the main point: frequency and magnitude are two different things. - Magnitude measures how much energy the earthquake releases at its source. - Frequency describes how fast the ground vibrates.