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.