Chapter 12 Earthquakes

12.1 How and Where Earthquakes Happen What we know: Earthquakes occur from too much pressure building up as the dynamic layers of the earth move Asthenosphere, Lithosphere. Most earthquakes occur near tectonic plates boundaries. Results from elastic rebound. In the process of elastic rebound, stress builds in rocks along a fault until they break and spring back to their original shape. (Pg 295)

12.1 Parts of an Earthquake Focus: The immediate location of the earthquake. Epicenter: The point above ground directly above the focus.

12.1 What happens after an earthquake? Earthquakes lets out two types of seismic waves: Body waves and Surface waves. Different seismic waves act differently pending on the material of earth’s interior through which they pass. Each type of wave travels at a different speed and causes different movements in Earth’s crust. (Pg 301) Body waves have P (compression) and S (shear) waves P waves travel through solid, liquid, and gas S waves only travel through solids

12.1 Shadow Zones Shadow Zones are areas of the Earth’s Surface where no direct seismic waves from a particular earthquakes can be detected. (Pg 298) Look at page 299 Draw the different convergent and divergent plate boundaries on the map provided. Use different colors to denotes the different plate boundaries.

12.2 Studying Earthquakes Scientists use seismographs to record earthquake vibrations Measured in seismograms The difference in the times that P waves and S waves take to arrive at a seismograph station helps scientists located the epicenter of an earthquake. Earthquake magnitude scales describe the strength of an earthquake. Intensity is a measure of the effects of an earthquake.

12.2 Studying Earthquakes Richter scale was used when I was a student Now the Mercalli Intensity Scale is used. Scale 1-12 (Pg 304) Common Earthquakes in America (Pg 308)

12.3 Earthquakes and Society Most earthquake damage is caused by the collapse of buildings and other structures. Tsunamis often are caused by ocean-floor earthquakes. People who follow safety guidelines are less likely to he harmed by an earthquake. Seismic gaps, tilting ground, and variations in rock properties are some of the changes in Earth’s crust that scientists use when trying to predict earthquakes.