Standard: Geo.3.d

1. Standard: Geo.3.d • Objectives • Content: Know the scales used to measure earthquakes. • Language: Take notes to compare the scales used to measure earthquakes. Mrs. Flores

2. 1. Warm-up • Where do most earthquakes occur? • Along existing faults at plate boundaries. • Why do earthquakes occur? • Plates slip and release elastic energy. • In what form does energy from an earthquake travel? • In the form of seismic waves. Mrs. Flores

3. 2. Seismic Waves • There are 3 kinds of seismic waves. • P (Primary) waves… • Cause particles to move back & forth. • Are fastest & first to arrive. Mrs. Flores

4. 2. Seismic Waves • S (Secondary) waves • Cause particles to move side to side. • Slowerthan P-waves but cause moredamage. Mrs. Flores

5. 2. Seismic waves • L (Surface) waves: • Radiate along the Earth’s surface. • Slowest but cause greatestdamage. Mrs. Flores

6. 3. Comparing Seismic waves • Circle the letter of the kind of seismic waves that are the slowest. • P waves • S waves • surface waves • Label the seismic waves compared below. P waves s waves Mrs. Flores

7. 4. Seismographs • Instruments called seismographs are used to measure seismic waves. • A heavy weight is attached to hang from a spring. • During an earthquake the graph paper jigglesup & down beneath the pen. Mrs. Flores

8. 5. Seismograms • Seismic waves are traced & electronically recorded on paper called Seismograms. • The size of the waves depends on the amount of slip. Mrs. Flores

9. 5. Seismograms • A seismogram shows all 3 types of seismic waves. • The waves arrive at different times because they travel at different speeds. • The greater the time between the arrival of the 1st P-wave & the 1st S-wave, the greater the distance to the epicenter. Mrs. Flores

10. 6. Wave Arrival Time • How far from the epicenter is a station that recorded 2 minutes between the 1st P-wave & 1st S-wave? • 1000 km • How about 4 minutes? • About 4000 km • How about 6 ½ minutes? • About 7000 km Mrs. Flores

11. 7. Locating the Epicenter • To find the epicenter, scientists use seismographs in 3 different locations. • Using differences in arrivaltime, a circle is drawn around each seismograph. • The point where the 3 circles intersect is the epicenter. Mrs. Flores

12. 8. Find the Epicenter • True or false? One seismograph can tell you exactly where an epicenter is. • False • On the map below, what point is the epicenter? • C Mrs. Flores

13. 9. Measuring earthquakes • Scientists use two different types of measurements to describe the size of an earthquake. • Intensity is the measure of the amount of shaking at a location based on the amount of damage. • This is not a quantitative measurement. Mrs. Flores

14. 9. Measuring earthquakes • Magnitude is a quantitative measurement that relies on calculations using seismograms. • Magnitude is the measure of the size of seismic waves or the amount of energyreleased. Mrs. Flores

15. 10. Scale used to measure intensity • Though intensity is subjective, it is still valuable in determiningdamage. • The modified Mercalli scale is used to measureintensity. • Lower numbers deal with the manner in which the earthquake is felt by people. • Higher numbers are based on observed structural damage. Mrs. Flores

16. 11. Scales used to measure magnitude • The Richter scale: • Measures the amplitude of the largestwave recorded on a seismogram. • 1point equals 10x more shaking. • Only useful for shallow earthquakes. • Though still used by the news, scientists no longer use this scale. Mrs. Flores

17. 11. Scales used to measure magnitude • The MomentMagnitude scale: • Based on the amount of energyreleased by an earthquake. • Measures displacement of fault, not ground movement. • 1 point equals32x more energy released. Mrs. Flores

18. 12. Closure • Fill in the blanks to complete the chart about ways to measure earthquake strength. Amplitude of seismic waves Moment magnitude scale Mrs. Flores