Earthquakes and Seismic Waves

Introduction Earthquake = the shaking and trembling that results from movement of rock beneath Earth’s surface Focus = area beneath Earth’s surface where rock under stress breaks and causes an earthquake Epicenter = point on the surface directly above the focus Intro to Earthquakes http://www.youtube.com/watch?v=JrBaiPN6AW8

Seismic Waves A. Earthquakes produce vibrations called Waves. B. Waves carry energy. C. Seismic waves are vibrations that travel through Earth carrying energy released during an earthquake. Earthquakes http://www.youtube.com/watch?v=YPhXXgjFwmg

Waves D. Seismic waves carry energy from an earthquake away from the focus, through Earth’s interior and across the surface. E. Three main categories of Waves: Primary Waves (P waves) Secondary Waves (S waves) Surface Waves Brain Pop Waves

Waves The first waves to arrive are Primary waves. P waves compress and expand the ground. After P waves come Secondary waves. S waves are seismic waves that vibrate from Side to Side as well as up and down. When P waves reach the surface, some of them become Surface waves. Surface waves move more slowly than P or S waves but they produce severe ground movements.

Seismic Wave Speeds Refer to Textbook ….page 56 Math Skills Answer Questions 1 – 4 X axis is Distance from Epicenter and Y axis is arrival time 2. 7.5 minutes 4 minutes 2000 = 3.5 minutes and 4000 = 4.5 minutes

Waves

Measuring Earthquakes There are at least 3 different measures for rating earthquakes. Two methods for measurement: Mercalli Scale Richter Scale Mercalli Scale = Rate earthquakes on the level of damage at a certain place Brain Pop Earthquakes

Mercalli Scale

Richter Scale Richter Scale = rating of an earthquake’s magnitude based on the size of the earthquake’s seismic waves Magnitude is a number geologists assign to an earthquake based on the earthquake’s size the seismic waves are measured by a seismograph How does a seismograph work? http://www.youtube.com/watch?v=Gbd1FcuLJLQ

Richter Scale

Comparing Magnitudes Comparing Magnitudes Moderate damage An earthquake’s magnitude tells Scientists how much energy was released by the earthquake Earthquakes with a Magnitude of 6 cause? Moderate damage 32 times the energy of a Magnitude 5 Quake

Locating the Epicenter Geologists use seismic waves to locate an earthquake’s epicenter.