They shake the ground underfoot, causing tremors that, at their worst, can leave cracks in highways and topple buildings. But for the most part, earthquakes are constantly rumbling through the Earth with a force that's barely detectable. But why do they occur? In All About Earthquakes, children will examine the forces at work that cause earthquakes and discover the instruments that scientists use to predict and measure these earthly tremors. A visit to Mammoth Lakes in California showcases an advanced network of lasers that measures ground movement in the area, while a fun, hands-on activity demonstrates how architects test their designs by using a shaker table. Part of the Earth Science for Children DVD Series. A Teacher's Guide is included and available online. 23 minutes. Grades K to 4.