Earthquakes are caused by forces deep within Earth's interior that continuously affect its surface. See also plate tectonics . One of its flaws is its imprecision in measuring the biggest earthquakes, those in the range of 8 or 9. Earthquakes in residential areas, such as this 1964 one in Seward, Alaska, can cause unparalleled damage to life and property. Different methods of measuring magnitude have superseded the Richter Scale , including surface-wave magnitude, which measures the seismic waves crackling around Earth's surface, and moment magnitude, the newest method, which is based on the size of the fault on which an earthquake occurs and the amount the Earth slips.
Moment magnitude is the most uniformly applicable scale.
More subjective and less scientific than magnitude, intensity is nevertheless a meaningful way of capturing the terror and destruction of an earthquake. It is the intensity of the 1906 San Francisco earthquake that is remembered, not its magnitude. The biggest earthquake of the century struck Chile on May 22, 1960. Its magnitude, the highest ever recorded, was 9.5. Tsunami The Alaskan Good Friday earthquake was followed by tsunami , or tidal waves, that reached 50 feet high and traveled a phenomenal 8,445 miles at 450 miles per hour.