Earthquakes can be so gentle that you wouldn’t even notice one. Or they shake the earth so fiercely that skyscrapers fall over and bridges collapse. Earthquakes are strongest at the epicenter, which lies directly above the hypocenter or focus of the quake.

Scientists have several ways to measure the strength of an earthquake. The Richter Scale is the most famous. It measures the size of the shock waves produced by the quake. Another scale, the Modified Mercalli Intensity Scale, measures the effects of an earthquake. It uses a series of key responses to the quake: waking people from sleep, moving furniture, breaking chimneys, and finally total destruction.

The magnitude of a quake isn't all that determines how much damage it does. The local geology is also important. In the same earthquake, the ground will shake much less if you're standing on bedrock than if sand or soft mud is underfoot. This is important information for engineers,since building on bedrock will require different types of seismic safety features than building on softer ground.

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