1. TAKE OUT HOMEWORK TAKE OUT HOMEWORK

2. SEISMIC WAVES

3. What is Seismology? Seismology is the study of earthquakes and seismic waves that move through and around the earth A seismologist is a scientist who studies earthquakes and seismic waves

4. What Are Seismic Waves? Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth. They are the energy that travels through the earth and is recorded on seismographs. Seismic comes form the Greek word meaning to “SHAKE”

5. Types of Seismic Waves Earthquakes produce 3 basic kinds of wave motions: P Waves S Waves L Waves

6. Primary Waves aka compressional waves back and forth wave motion this motion alternates squeezing and stretching the rock through which it passes can travel through any material- solid rock, magma, ocean water, and air travel about twice as fast as S waves.

7. S Wave-Secondary Waves aka Shear Wave side to side waves cause particles to move at right angles to the direction the waves are traveling can travel through solids but not through liquids or gases

8. L Waves-Surface Waves When P and S waves reach the surface, they set up a third wave called L waves or surface waves These waves move like “ripples” on a pond and travel more slowly than P or S waves

9. P Waves (Primary or Compressional) S Waves (Secondary or Shear) L Waves (Surface) Back & Forth motion Side to Side motion “Ripples” on a pond travel through: solid rock, magma, ocean water, and air travel thru: Solids but not liquids or gases. Surface Waves Fastest, first to reach seismograph Twice as Slow as P waves, reach second Slowest, last to reach seismograph

10. How Do Seismologists Measure earthquake waves? Seismographs are instruments that detect and record earthquake waves

11. Earthquakes are measured according to the RICHTER SCALE. This is based on the size of the largest seismic wave produced by the earthquake. Earthquakes are measured according to the RICHTER SCALE. This is based on the size of the largest seismic wave produced by the earthquake.RICHTER SCALERICHTER SCALE The damage done by an earthquake is measured according to the MERCALI SCALE. The damage done by an earthquake is measured according to the MERCALI SCALE.MERCALI SCALE.MERCALI SCALE.

13. Modified Mercalli Scale Inten sity Verbal Description Magnit ude Witness Observations IInstrumental1 to 2Detected only by seismographs IIFeeble2 to 3Noticed only by sensitive people IIISlight3 to 4Resembling vibrations caused by heavy traffic IVModerate4Felt by people walking; rocking of free standing objects V Rather Strong 4 to 5Sleepers awakened and bells ring VIStrong5 to 6Trees sway, some damage from overturning and falling object VIIVery Strong6General alarm, cracking of walls VIIIDestructive6 to 7Chimneys fall and there is some damage to buildings IXRuinous7Ground begins to crack, houses begin to collapse and pipes break XDisasterous7 to 8 Ground badly cracked and many buildings are destroyed.There are some landslides XI Very Disasterous 8 Few buildings remain standing; bridges and railways destroyed;water, gas, electricity and telephones out of action. XIICatastrophic 8 or greater Total destruction; objects are thrown into the air,much heaving,shaking and distortion of the ground

14. What Do Seismologists Learn From Seismic Waves? Seismologists use seismographs to record the amount of time it takes seismic waves to travel through different layers of the Earth. As the waves travel through different densities, seismologists can deduce the type of material the waves are travelling through. The results can provide a snapshot of the Earth’s internal structure and help us to locate and understand fault planes and the stresses and strains acting on them.

15. Results of Seismic Waves

20. TRIVIA QUESTIONS What is the most earthquake prone state in the US? ALASKA- it’s one of the most seismically active regions of the world Why does California have so many EQ’s and NY does not? CA is on a plate boundary What states have the least amount of EQ’s? Florida and N. Dakota Where and when did the largest EQ occur in the 20 th Century? 1960 Chilean EQ: Magnitude 9.6 and broke a fault over 1,000 miles long!