CONTENTS WHAT ARE EARTHQUAKES 4 PLATE TECTONICS 6 WHERE DO EARTHQUAKES HAPPEN 8 EARTHQUAKES AND VOLCANOES 10 EARTHQUAKES AND TSUNAMIS 12 SHOCK WAVES 14 MEASURING EARTHQUAKES 16 FORESHOCKS AFTERSHOCKS AND SWARMS 18 EARTHQUAKE PREDICTION AND WARNING SYSTEMS 22 DAMAGE FROM EARTHQUAKES 24 EARTHQUAKE SAFETY 26 EARTHQUAKES MAKE HISTORY 28 GLOSSARY 30 FOR MORE INFORMATION 31 INDEX 32
WHAT ARE EARTHQUAKES In an earthquake huge masses of rock move beneath Earth’s surface and cause the ground to shake Earthquakes also called temblors are happening all the time around the world Often they are too small for people to feel A powerful earthquake hit eastern Alaska in 2002 When the ground shakes roads and buildings can be damaged Most earthquakes are caused by changes in Earth’s outermost shell or crust The crust is made up of about a dozen dozen masses of rock called plates In different places plates move 4
THINK ABOUT IT Earthquakes can be frightening Why do you think people used to wonder if the earth shaking was caused by gods or monsters core 4 300 miles apart collide or slide past each other Over time movement causes pressure to increase When pressure becomes too great the rock masses suddenly shift along a crack in the crust called a fault The shifting rocks release energy in the form of shock waves These waves spread through the rock in all directions causing an earthquake In the most powerful quakes people thousands of miles away can feel the ground shake mantle 1 800 miles crust 3 19 miles 2014 Encyclopædia Britannica Inc Earth has three main layers a thin rocky crust a thick rocky mantle and a metallic core
