Earthquakes Sections 6.2 and 6.3

Section 6.2 – Recording Earthquakes Seismic waves are recorded using a seismograph A seismograph is made of 3 separate devices One measures up and down movement While the other 2 measure North-South and East-West movements

Section 6.2 – Recording Earthquakes There are 3 kinds of seismic waves Primary Waves (P waves) – move the fastest and can travel through solids and liquids. P waves are detected first Secondary Waves (S waves) – are slower and can only travel through solid rock. S waves are detected second Surface Waves – are the slowest. They occur when P and S waves reach the surface and cause lots of Damage

Section 6.2 – Recording Earthquakes It takes 3 seismographs to locate the epicenter of an earthquake The difference in amount of time it takes the P and S waves to reach each seismograph determines how far away the earthquake occurred.

Section 6.2 – Recording Earthquakes Magnitude is a measure of the energy released by an earthquake and it describes the amount of ground motion The Richter scale shows how much damage is expected by the earthquake

Section 6.2 – Recording Earthquakes Large earthquakes have a magnitude above 7 Moderate are between 6 and 7 Minor are between 2.5 and 6 Microquakes are below 2.5 and aren’t felt by people

Section 6.3 – Earthquake Damage During severe earthquakes you would be much safer in an open field than in a city of skyscrapers Large buildings sway and the fall over Buildings built on loose soil are more likely to fall than those on solid ground

Section 6.3 – Earthquake Damage A Tsunami is formed when a major earthquake happens on the ocean floor A tsunami is a giant ocean wave Tsunamis can also be caused by under water landslides

Section 6.3 – Earthquake Damage Earthquakes are very hard to predict Along some faults, scientists have identified zones of rock that are locked in to position This is called a seismic gap.