Earthquakes

1. Earthquakes

2. Lesson Essential Question How do earthquakes result from the buildup of energy in rocks?

3. Earthquakes- What , Why, How and Where What-An earthquake is the vibration caused by the breaking of rock. Why-The earth’s surface is in constant motion because of the forces inside the planet. These forces cause earth’s plates to move. This movement puts stress on the rocks near the edges of plates. How-To relieve this stress, the rocks tend to bend, compress, or stretch(EPE). If the stress is great enough the rocks will break and move (KE) along surfaces called faults.

4. How Earthquakes Occur When stressed rock exceeds its elastic limit, it breaks, moves along a fault, and then returns to its original shape. The energy needed to bend the rock is stored as elastic potential energy (EPE). If the force bending the rock is removed, the rock will return to its original shape and the stored energy will be released as energy of motion(KE). Result: within the earth’s crust=EPE-KE-TE.

5. EARTHQUAKES • Caused by plate tectonic stresses • Located at plate boundaries • Resulting in breakage of the Earth’s brittle crust

6. Fault Motion At faults, rocks can move up, down, or sideways in relation to rock along the other side of the fault .

7. Understanding Faults- Hanging and Foot Wall The foot wall is the wall below the fault line. The rock here does not move. The hanging wall is the rock above the fault line. It can move up, down, to the side or on top of the other rock.

8. Three Types of Force Compression is the force that squeezes rock together. Tension is the force that pulls rocks apart. Shear is the force that causes rocks on either side of a fault to slide past each other.

9. Faults Tension causes rocks to be pulled apart and the rocks move down along the fault line. Compression causes rocks to squeeze together and rocks move up along a fault line. Strike slip is side by side motion along the fault line.

10. Normal Fault Normal faults are caused by tensional forces that cause rocks to be pulled apart. In a normal fault, the hanging wall rock will move down along the fault line(gravity-pulls down).

11. Reverse Faults Reverse faults are caused by compression forces squeezing rocks together. In a reverse fault, the hanging wall will move up along the fault line.

12. Strike-Slip Fault At a strike-slip fault, rocks on either side of the fault are moving past each other without much upward or downward movement. They are also called right lateral and left lateral faults. The San Andreas Fault is an example of a strike-slip fault.

13. San Andreas Fault The San Andreas fault extends 960 km from Mexico to the north of California. The land to the west is moving north. The land to the east of the fault is moving south. All the rocks do not move at the same time so earthquakes occur in one area and then another.

15. Earth Science Read and Review Assignment • Read pages 300- 303 • On a piece of paper for turn –in: • Answer the reading check questions on pages: 301 and 303. • Answer the Section Review Self Check questions 1-5 on page 303

16. Features of Earthquakes Seismic Waves are the waves of energy generated by an earthquake. There are three main types of seismic waves. Primary (P waves) Secondary (S waves) Surface (L waves) All the waves are generated at the same time but their speed varies.

17. EARTHQUAKE WAVES • FOCUS = place deep within the Earth and along the fault where rupture occurs • EPICENTER = geographic point on surface directly above focus • SEISMIC WAVESproduced by the release of energy • move out in circles from the point of rupture (focus) • 2 types: surface & body (travel inside & through earth’s layers) • P waves: back and forth movement of rock; travel thru solid, liquid, gas • S waves: sideways movement of rock; travel thru solids only

18. EARTHQUAKE WAVES P waves move through solids & liquids S waves move through solids only!!!

19. Seismograph An instrument used to detect and measure seismic waves. A weight attached to a spring remains nearly still even when the Earth moves. A pen attached to the weight records any movement on a roll of paper on a constantly rotating drum. The drum moves with the Earth and affects the line.

20. EARTHQUAKE WAVES • Seismographs record earthquake waves • Seismograms show: • Amplitude of seismic waves (how much rock moves or vibrates) • Distance to the epicenter • Earthquake direction

21. EARTHQUAKE WAVES • 3 types of seismic waves show up on seismogram • P waves: shake earth in same direction as wave; travel thru solid, liquid, gas • S waves: Shake earth sideways to wave direction; travel thru solids only • Surface waves: circular movement of rock; travel on surface – cause most damage!!

22. EARTHQUAKE WAVES Lets test your understanding!! Is this a P or an S wave? P wave! S Wave

23. EARTHQUAKE WAVES Primary (1st to arrive)Longitudinal, Compression Secondary (2nd to arrive - larger) Transverse, Shear all states of matter (solid, liquid, gas) Can go through solids only • back and forth movement of rock • push/pull or compression/stretch out • Like slinky down stairs • Vibration is same as the direction of travel • Move sideways • perpendicular to direction of wave travel • Like snake

24. Surface Waves The slowest moving seismic waves are called surface waves or L waves. L waves originate on the Earth’s surface at the epicenter. They move along the surface the way waves travel in the ocean. The Earth’s surface moves up and down and side to side with each L wave. L waves cause most of the damage.

25. HOW TO READ SEISMOGRAMS • P & S (body waves) move through earth & arrive first • P & S waves used to calculate magnitude of earthquake • Amplitude = height of wave (how much the rock moves; size of vibration)

26. Seismograph Stations Each type of wave reaches a seismograph station at a different times. Primary waves arrive first. Secondary waves travel slower and arrive later. The difference in arrival time is used to estimate the distance from the station to the epicenter.

27. Locating an Epicenter Scientists need readings from three or more stations to determine the location. A circle is drawn around each station. The radius of each circle is equal to the station’s distance from the epicenter. The point of intersection is the location of the epicenter.

28. Information from Earthquakes Earthquakes and the study of seismic waves have provided seismologist with much of the their information about the Earth’s interior. A seismologist is geologist who studies earthquakes and seismic wave activity. Seismologist have constructed a model of the earth’s interior based on seismic wave behavior.

29. Determining the Earth’s Layers Seismologist view the earth’s interior as consisting of layers of increasing density from crust to core. They determined the speed of seismic waves varies with the rigidity and density of the material they pass through. The denser the material the faster the speed. Seismic waves slow down in molten rock. Layer boundary were established based on significant changes in wave speed.

30. Elements in the Earth’s Crust

31. Earth’s Layers Crust-outermost layer, rigid and brittle, made up mostly of oxygen, silicon, aluminum, magnesium and iron Outer Mantle directly below the crust, it along with the crust makes up the lithosphere (earth’s plates). Consists primarily of: silicon, oxygen, magnesium and iron.

32. Earth’s Layers Asthenosphere-a portion of the upper mantle, consist of weak rock that can flow slowly. The lithosphere moves on the convection currents driving the motion of the asthenosphere. Lower mantle-denser molten rock with same elemental make-up as upper mantle. Outer core- (liquid) made mainly of iron and nickel. Inner Core- solid due to tremendous pressure, it’s made mainly of iron with small amounts of nickel, oxygen, silicon and sulfur.

33. The Mohorovicic Discontinuity(Moho) Seismic waves change speed as they move through the earth’s layers. when they pass through the bottom of the crust and enter the mantle they speed up. The boundary between the crust and upper mantle is called the Mohorovicic Discontinuity or Moho.

34. Seismic Speed in the Core The core is divided into two layers based on how seismic waves travel through it. Primary waves slow down and secondary waves do not travel through the liquid outer core. Primary waves speed up again when they reach the solid inner core. The density of the material a wave travels through determines the speed of the wave; the greater the density the greater the speed.

35. Shadow Zone Because the P waves bend and the S waves can’t travel through liquids there is an area of the Earth between 105 and 140 degrees from the Earthquake epicenter that does not receive any seismic waves. This is called the shadow zone.

36. Earth Science Read and Review Assignment • Read pages 304- 311 • On a piece of paper for turn –in: • Answer the reading check questions on pages: 305, 309 and 310. • Answer the Section Review Self Check questions 1-6 on page 311. • Do Mini Lab, "Interpreting Seismic Wave Data,” on page 309. Follow procedures and answer the Analysis Questions.

37. People and Earthquakes Predicting Earthquakes • Frequency of small tremors can precede a large earthquake. • Changes in P and S waves speeds arriving at monitoring stations often indicated a more intensive earthquake. • Animals behavior is affected by tremors. (ex.) Snakes leave their underground homes in the winter.

38. Earthquake Damage Depends on: The earthquake’s strength(magnitude). The kind of rock and soil that underlies an area The kind of buildings in the area The time at which the earthquake occurs The population of the area

39. EARTHQUAKE DAMAGE Most caused by SURFACE waves (arrive last)

40. EARTHQUAKE DAMAGE • Landsides • Building damage • Liquefaction

41. Liquefaction The shaking from an earthquake can cause wet soil to act more like a liquid. If liquefaction occurs under a building, the building can sink into the soil and collapse.

42. LIQUEFACTION when a solid (sand and soil) becomes saturated with water and acts like a heavy liquid • Results in a loss of soil strength & the ability of the soil to support weight

43. Scales Used to Measure Earthquakes The Richter scale is used to calculate the strength (magnitude) of an earthquake. The Modified Mercalli is used to measure the intensity (amount of destruction) of an earthquake.

44. The Richter Scale measures the strength or magnitude An increase of one magnitude on the Richter scale means that 32 times more energy is released. An earthquake of magnitude 6 is 32 x 32 x 32 times greater than an earthquake with a magnitude of 3.

45. Magnitude The height of the lines traced on the paper of a seismograph is a measure of the energy that is released, or the magnitude of an earthquake.

46. The Modified Mercalli Scale measures the amount of damage The Modified Mercalli scale describes the intensity of an earthquake using the amount of structural and geologic damage in a location.

47. MERCALLI VS. RICHTER

48. ISOSEISMIC MAPS • Connects areas of with the same Modified Mercalli number • Areas are colored according to Modified Mercalli number Loma Prieta Earthquake 1989 show the distribution of intensities

49. Seismic Risk Map of the U.S.

50. Tsunamis-”Harbor Wave” Earthquakes which occur on the ocean floor can produce giant sea waves called tsunamis. Tsunamis can travel at speeds of 350 -400 mph. As they approach the coast, they can reach heights of greater than 100 feet. The Tsunami Warning Center is located in Hilo, Hawaii.