Understanding Earthquakes: Causes, Types, and Effects

1. Notes Points Name __________________________________ Period _______ J. Nguyen – Physical Science

2. Chapter 12 Standard 3d. Students know why and earthquakes occur and the scales used to measure their intensity and magnitude. J. Nguyen – Physical Science

3. Chapter 12 – Earthquakes J. Nguyen – Physical Science

4. I. 11.1 FAULTS J. Nguyen – Physical Science

5. A. Stress and faults • The Earth’s lithosphere is constantly moving. During this move, rocks in the crust are squeezed, stretched, and twisted resulting in force being exerted onto the rocks. The force on each unit of area is called stress.

6. Stress occur in the Earth’s crust at divergent, convergent and transform boundaries. • Stress can cause rocks to break. There are two categories of rock breakage: • Fracture is a break where there is no movement of the surrounding rock. • Fault is a break where there is movement of the surrounding rock.

7. B. There are different types of faults. • Normal fault • Type of fault in which the hanging wall moves downward relative to the footwall • Reverse fault • Type of fault in which the hanging wall moves upward relative to the footwall • Thrust fault • Type of reverse fault in which the fault plane is at a low angle or nearly horizontal. • Strike-Slip fault • Rock on either side of the fault plane slides, or slips, horizontally

8. Color and label the picture. footwall hanging wall hanging wall footwall hanging wall footwall Types of Faults

9. Write 5 questions for this section. Highlight key words and phrases. J. Nguyen – Physical Science

10. II. 12.1 HOW AND WHERE EARTHQUAKES HAPPEN J. Nguyen – Physical Science

11. A. What are earthquakes? • Earthquakes are movements of the ground that are caused by a sudden release of energy when rocks along a fault move. • The rocks may move suddenly and without warning.

12. B. Why do earthquakes happen? • Geologists think earthquakes are a result of elastic rebound. • Elastic rebound is the sudden return of elastically deformed rock to its undeformed shape. • When plates move, rocks on either side of a fault bend or deform. Rocks build up stress when they bend. This stores energy in the rock. • When enough stress builds, rocks release their accumulated energy and rebound or spring back to their original shape. • This “rebound” results in an earthquake.

13. Color the picture. Elastic Rebound

14. C. Anatomy of an earthquake The focus is the location within the Earth where the first motion of the earthquake occurs. The epicenter is the point on the Earth’s surface directly above the focus. Vibrations start from the focus and radiate outward and eventually towards the surface. Earthquakes with the most damage usually have shallow foci because there is still a lot of energy by the time the vibrations reach the surface.

15. Anatomy of an Earthquake Color and label the picture. (energy)

16. D. Rocks release energy in the form of seismic waves. Seismic waves are the form of vibrations released from rocks during an earthquake. The waves travel outward in all directions. There are two main types of waves.

17. E. The two main types of seismic waves are body waves and surface waves. • Body waves are waves that travel through the body of a medium. There are two types: • P waves (primary or compression waves) • fastest of the body waves • the first wave to be detected • causes rocks to move back-and-forth that is parallel to the movement of the waves • can travel through solids, liquids and gases • moves faster through rigid material

18. S waves (secondary or shear waves) • slowest of the body waves • arrives after P waves • causes rocks to move in a side-to-side direction that is perpendicular to the waves • can travel only through solids

19. Surface waves are waves that travel along the surface rather than through the middle and are the slowest-moving waves. There are two types: • Love waves • cause rock to move side-to-side and perpendicular to the waves • Rayleigh waves • cause ground to move with a rolling motion

20. Types of Waves Color and label the picture.

21. F. Seismic waves help scientists learn about the Earth’s interior. The speed and direction of P waves and S waves are affected by the material they travel through. By studying the speed and direction of seismic waves, scientists have been able to locate the layers of the Earth. Seismic waves also show shadow zones which are location on Earth’s surface where no body waves can be detected since the Earth’s interior are not uniform in rigidity.

22. Shadow Zones Color and label the picture.

23. G. Earthquakes and plate tectonics • Earthquakes are the result of stresses in Earth’s lithosphere. There are three main tectonic plate boundaries where stress on the rock is greatest. • convergent oceanic plates • Two plates are moving towards each other with one plate subducting or sinking under the other plate • As the top plate scrapes across the bottom plate, earthquakes occur. • divergent oceanic plates • Two plates are moving away from each other. • The spreading motion causes earthquakes. • continental plates • Two continental plates are moving away, towards or in opposite directions to each other. • Any of those movements causes earthquakes.

24. H. Earthquakes and fault zones At some plate boundaries, there are fault zones which are regions of closely spaced faults. Some earthquakes are not caused by movements along plate boundaries but can be caused by an ancient fault zone deep within the Earth’s crust.

25. Write 10 questions for this section. You should have 15 questions so far. Highlight key words and phrases. Draw a picture. J. Nguyen – Physical Science

26. Summary (two paragraphs) – Page 4 Stress is ____________________________. Fault is _____________________________. The different types of faults are (choose any 2) ___________ and ________. Earthquakes are ___________________. Scientists believe earthquakes happen because of ___________________. The focus is the __________________whereas the epicenter is the _____________________. The two types of seismic waves are ___________ and ____________. There are two types of body waves which are _________ and _________. There are two types of surface waves which are _________ and ___________. Seismic waves help scientists learn about the Earth’s ___________. J. Nguyen – Physical Science

27. III. 12.2 STUDYING EARTHQUAKES

28. A. Earthquakes are recorded. • Seismology is the study of earthquakes and seismic waves. • Seismograph is an instrument that records and detects vibrations in the ground. • One device records the vertical motion of the ground. • A second device records the horizontal east-west motion. • A third device records the horizontal north-south motion.

29. Label the picture. • Seismogram is the recording or tracing of the earthquake motion. • P waves are recorded first since they are the fastest. • S waves are recorded second. • Rayleigh and Love waves are recorded last.

30. B. Earthquakes (epicenters) are located using two techniques. • Scientists look at the arrival times of both the P waves and S waves. • The longer the lag time between the two, the further the epicenter. • Scientists use computers to perform complex triangulations. • Information is used from several seismograph stations to pinpoint the location of the epicenter.

31. C. Earthquakes are measured by magnitude and intensity. • Magnitude is the measure of the strength of an earthquake. The larger the magnitude, the greater the energy of the earthquake. Magnitude has two scales: • The Richter scale measures the ground motion from an earthquake to find the earthquake’s strength. • Moment magnitude is a measurement of earthquake strength based on three factors: • size of the area of the fault that moves • the average distance that the fault blocks move • the rigidity of the rocks in the fault zone.

32. Intensity is the measure of the effects of an earthquake. Intensity has one scale: • Mercalli scale expresses intensity and provides a description of the effects of each earthquake intensity.

33. IV. 12.3 EARTHQUAKES AND SOCIETY

34. A. Earthquakes cause much damage. Earthquakes with epicenters on the ocean floor may cause a giant ocean wave called a tsunami. can cause much damage when the waves crashes into land Buildings whose walls are too weak to withstand the swaying motions of an earthquake may collapse completely.

35. B. There are earthquake safety measures. • Before an earthquake • Be prepared by keeping the appropriate supplies on hand. • During an earthquake • Stay calm while moving to a safer position. • After an earthquake • Be cautious and check for hazards.

36. C. Can earthquakes be predicted? • Scientists study past earthquakes to predict where future earthquakes are most likely to occur. However, there is currently no reliable way to predict exactly when or where an earthquake will occur. • Scientists have identified zones of low earthquake activity, or seismic gaps. • A seismic gap is an area along a fault where relatively few earthquakes have occurred recently but where strong earthquakes occurred in the past. • Some earthquakes are preceded by foreshocks but this is not a successful method to predict earthquakes. • Scientists continue to study seismic activity so they may one day make accurate forecasts and save more lives.

37. Areas with earthquake hazard levels Color the picture.

38. Write 10 questions for this section. You should have a total of 25 questions. Highlight key words and phrases. Draw a picture. J. Nguyen – Physical Science

39. Summary (one paragraph) – Page 6 Seismology is _________________________. A seismogram is _______________________. P waves are recorded ______ since they are the __________. ___ waves are the second. Earthquakes are measured by ___________ and ____________. Magnitude is __________ ___________________ while intensity is _____________________. J. Nguyen – Physical Science

40. Notes Points Name __________________________________ Period _______ J. Nguyen – Physical Science