Earthquakes and Seismic Waves Chapter 2 Section 1 Objectives F.2.2.1. Describe how the energy of an earthquake travels through Earth. F.2.2.2. Identify the scales that are used to measure the strength of an earthquake. F.2.2.3. Explain how seismologists find the epicenter of an earthquake. Start Epicenter Lab What is an earthquake? An earthquake is the shaking of the ground that results from the movement of rock in the ground. Does anyone remember what I told you earlier causes earthquakes? It’s the rebound, or the rock returning to it’s original shape after deformation. Elastic Rebound Earthquake Focus The focus is the spot beneath the ground where the disturbance originates. Earthquake Epicenter The epicenter is the spot on the surface of the ground directly above the focus. Types of Seismic Waves What are the three types of seismic waves? Primary Waves Secondary Waves Surface Waves Primary Waves Primary waves move the particles back and forth parallel to the direction of the wave. Secondary Waves Secondary waves move the particle up and down perpendicular to the direction of the wave. Surface Waves Surface waves combine both vectors and produce a rolling motion. Primary Wave Secondary Wave Surface Wave Surface Wave How To Reduce The Effect Of Ground Shaking Wave In RR Tracks Measuring Earthquakes The three common scales used to measure an earthquake are: Mercalli Scale Richter Scale Moment Magnitude Scale Earthquake Scales Mercalli Scale Looks at the damage caused. See Figure 9 on page 55 in your book. Richter Scale Looks at the size of the seismic waves on the seismograph. Seismograph & Seismogram Seismograph Seismogram How A Seismograph Works Comparing Magnitudes The intensity of an earthquake increases about 32x’s for each step. A 5 is 32x’s more intense than a 4 and a 6 is about how much stronger. Think 32 x 32= 1000 times stronger Locating an Epicenter Why do we need three locations to find the epicenter of an earthquake? To pinpoint the location through triangulation. Locating the Epicenter Locating the Epicenter U.S. Earthquake Risk Map Begin Epicenter Lab See pages 57-59 in your textbook for more detailed procedures.