FOCUS ON Contents What is an Earthquake Tectonic Plates Plate Boundaries and Faults San Francisco 1906 Measuring Earthquakes Earthquake Hazards FOCUS ON Peru 1970 Earthquakes and Buildings Rescue and Relief FOCUS ON Nepal 2015 Preparing for Earthquakes Tsunamis FOCUS ON Japan 2011 Glossary Test Yourself Index 4 6 8 10 12 14 16 18 20 22 24 26 28 30 31 32
What is an Earthquake An earthquake is the shaking of the ground caused by movements in the Earth’s crust During a large earthquake the ground shakes violently and buildings collapse Cracks appear in the ground and loud noises ring through the air as structures and objects fall For people who live in earthquake-prone areas quakes are a constant risk Shockwaves Movement in the Earth’s crust the outer layer of the Earth causes strain to build up between large plates or blocks of rock trying to move past each other Stored energy is released in giant shockwaves called seismic waves These intense vibrations cause damage to buildings and streets FOCUS ON San Francisco 1906 page 10 Regular events Scientists estimate that there are several million earthquakes every year However the huge majority of them go unnoticed as they are too small to be detected or happen in remote areas 4 FOCUS ON Peru 1970 page 16
FOCUS ON Nepal 2015 page 22 Multiple shocks Large earthquakes are not usually single events They are normally preceded or followed by foreshocks and aftershocks These are smaller earthquakes that happen before and after the main earthquake also called the mainshock Aftershocks can be particularly dangerous for residents and people working on relief efforts FOCUS ON Japan 2011 page 28 Duration Most earthquakes are only a few seconds long averaging between 10 and 30 seconds However some last up to a few minutes such as the 2011 earthquake in Japan which lasted six minutes 5 Indian Ocean Tsunami 2005 page 27
