1. Chapter 16 Earthquakes

2. What is an earthquake? Shaking of the ground caused by the sudden release of energy stored in the rocks.Shaking of the ground caused by the sudden release of energy stored in the rocks. When rocks are stressed, potential energy is stored in them.When rocks are stressed, potential energy is stored in them.

3. Rocks can behave plastically upto a certain limit (elastic limit), after which they fail and release the energy.Rocks can behave plastically upto a certain limit (elastic limit), after which they fail and release the energy. Energy waves produced by an earthquake are called Seismic Waves.Energy waves produced by an earthquake are called Seismic Waves.

4. The generation of an earthquake is explained by Elastic Rebound Theory.The generation of an earthquake is explained by Elastic Rebound Theory. According to this theory, the sudden release of progressively stored strain in rocks causes movement along a fault and an earthquake is generated.According to this theory, the sudden release of progressively stored strain in rocks causes movement along a fault and an earthquake is generated.

12. Causes of earthquakes Movement along a faultMovement along a fault Volcanic eruptionsVolcanic eruptions Plate movementPlate movement SubsidenceSubsidence

13. Earthquake terminology Focus: the point inside the earth where seismic waves first generate.Focus: the point inside the earth where seismic waves first generate. Epicenter: the point on ground surface directly above the focus. It may be any geographic locality.Epicenter: the point on ground surface directly above the focus. It may be any geographic locality.

15. Seismic waves 2 types2 types –Body waves: traveling inside the earth –Surface waves: travel on the earth’s surface.

16. Body waves:Body waves: –P-waves (primary) –S-waves (secondary) P-wave: is the fastest (4-7 km/sec) and is the first to arrive at a recording station.P-wave: is the fastest (4-7 km/sec) and is the first to arrive at a recording station.

17. P-wave: compressional or longitudinal wave in which rocks vibrate back and forth parallel to the direction of wave propagation.P-wave: compressional or longitudinal wave in which rocks vibrate back and forth parallel to the direction of wave propagation.

19. S-wave: slower (2-5 km/sec) and arrives after the P-wave at a recording station.S-wave: slower (2-5 km/sec) and arrives after the P-wave at a recording station. It’s a transverse wave in which the rock vibrates perpendicular to the direction of wave propagation.It’s a transverse wave in which the rock vibrates perpendicular to the direction of wave propagation.

21. Surface waves:Surface waves: –slowest waves generated by an earthquake. –They take longer to pass and cause more property damage.

22. Love waves: the ground moves side to side in a horizontal plane that is perpendicular to the direction of wave travel.

24. Rayleigh waves: the ground moves perpendicular to the direction of wave travel. They are like ocean currents.

26. EQ measurement The instrument used to measure an EQ is called a seismometer.The instrument used to measure an EQ is called a seismometer.

29. Seismograph: paper or electronic record of an EQ.

31. World seismograph stations

34. Locating EQ Epicenter Travel time of the seismic waves from the focus to the seismograph station is used to determine the EQ epicenter.Travel time of the seismic waves from the focus to the seismograph station is used to determine the EQ epicenter. P and S waves gradually separate because they travel at different velocities.P and S waves gradually separate because they travel at different velocities.

36. The P-S interval is compared with a standard travel-time curve.

38. Data from one station can be used to determine only distance to the station and not the direction.Data from one station can be used to determine only distance to the station and not the direction. At least three stations are required to determine the location of the epicenter.At least three stations are required to determine the location of the epicenter.

40. Measuring the size of an EQ Two ways of determining the EQ size;Two ways of determining the EQ size; –Intensity –Magnitude

41. Measuring the size of an EQ EQ Intensity: it is a measure of how an area has been damaged by the EQ.EQ Intensity: it is a measure of how an area has been damaged by the EQ. Modified Mercalli Scale is used to measure intensity.Modified Mercalli Scale is used to measure intensity.

49. EQ magnitude: it’s a measure of the amount of energy released by an EQ.EQ magnitude: it’s a measure of the amount of energy released by an EQ. EQ magnitude is reported on the Richter scale.EQ magnitude is reported on the Richter scale.

50. It is done by measuring the height (amplitude) of a specific wave.It is done by measuring the height (amplitude) of a specific wave. ML = log10A(mm) + (Distance correction factor)ML = log10A(mm) + (Distance correction factor)

52. Magnitude (log Scale) Possible Effects 1-2Normally only detected by instruments 3Only faintly felt 4Faint tremor causing little damage 5Structural damage 6Distinct shaking, less well-constructed buildings collapse 7Most buildings destroyed 8Major structures destroyed 9Ground seems to shake-catastrophic

58. Effects of EQ Primary effects: occur immediately from ground shakingPrimary effects: occur immediately from ground shaking Secondary effects: damage caused by;Secondary effects: damage caused by;

59. Effects of EQ –Floods –Fire –Landslides –Liquefaction: wet, saturated soil changes from solid to liquid as a result of shaking. –Tsunamis

62. Global distribution of EQ 3 belts;3 belts; –Circum-Pacific belt –Mediterranean-Himalayan belt –Continental interior

70. Mitigating EQ effects Avoiding EQ prone zones Foundation design Structural modifications Building codes

71. Predicting EQ Rock monitoring: rock properties begin to change before its failure. Water levels: increase or decrease. Radon emission: increases before an EQ.

72. Predicting EQ Seismic gap: regular pattern of EQ occurrence. Animal behavior: snakes, dogs.

73. Assignment 2 Rivers, groundwater, lakes Ohio EPA Great lakes, lake erie Relative proportions Maximum Contaminant Level Primary contaminants Secondary Water resources of Ohio: are they contaminated? 3-4 page typed report Due: Friday, Nov. 19