Science Explorer: Inside Earth



Science Explorer: Inside Earth

Chapter 2 – “Earthquakes”

** All answers are to be in complete sentences for credit.

Section 1

1. What is an earthquake defined as?

An earthquake in the shaking and trembling that results from the movement of rock beneath the earth’s surface.

2. What is stress defined as?

A stress is a force that acts on rock and changes its shape or volume.

3. Describe shearing.

Shearing is a stress that pushes a mass of rock in two opposite directions.

4. Describe compression.

Compression is a forces that squeezes rock until it folds or breaks.

5. Describe tension.

Tension is a force that pulls on the crust, stretching rock so that it becomes thinner in the middle.

6. How do the above three forces affect the Earth’s surface?

Shearing, compression, and tension work over millions of years to change the shape and volume of rock.

7. What is a fault?

A fault is a break in the rock of the crust where rock surfaces slip past each other.

8. Where are faults generally located?

Faults occur along plate boundaries where the forces of plate motion push or pull the crust so much that the crust breaks.

9. Describe a strike-slip fault.

In a strike-slip fault, the rocks on either side of the fault slip past each other side-ways with little up or down motion.

10. Describe a normal fault.

In a normal fault, tension in earth’s crust pulls rocks apart. The fault is at an angle so one block of rock lies above the fault while the other block lies below the fault. The block of rock that lies above the fault is the hanging wall, and the rock that lies below is the footwall. The hanging wall moves down.

11. Describe a reverse fault.

In a reverse fault compression moves the rocks in the opposite direct of a normal fault. The hanging wall moves up relative to the footwall.

12. What are folds defined as?

Folds are bends in rock that form when compression shortens and thickens part of Earth’s crust.

13. Folds can range from what distance to what distance?

Folds can be a few centimeters across or hundreds of kilometers wide.

14. Give an example of a mountain range that is a folded mountain range.

The central Appalachian Mountains in Pennsylvania are an example of a folded mountain range.

15. What is an anticline?

An anticline is folded rock that bends upward into an arch.

16. What is a syncline?

A syncline is a fold in a rock that bends down to form a valley.

17. What type of force produces an anticline & syncline?

A compression force

18. How are fault block mountain ranges formed? Give an example.

When two normal faults cut through a block of rock, a fault block mountain forms.

19. How are valleys formed by faults?

A valley is formed when a fold in a rock bends down.

20. What is a plateau?

A large area of flat land elevated high above sea level.

21. Where is the Colorado plateau found? Describe how high and how large is it.

Where Arizona, Utah, Colorado, and New Mexico meet

The plateau 1,500 meters above sea level

Section 2

22. What is the focus defined as?

The focus is the area beneath earth’s surface where rock that is under stress breaks and triggers and earthquake.

23. What is the epicenter defined as?

The epicenter is the point on the surface directly above the focus.

24. What are the three classes of seismic waves?

The three categories of seismic waves are S waves, P waves and surface waves.

25. What is the Mercalli scale?

The Mercalli scale is a scale that rates earthquakes from 1-12 according to the level of damage at a given place.

26. What does a seismograph do?

A seismograph is an instrument that measures seismic waves.

27. What is magnitude?

The magnitude is a number that geologists assign to an earthquake based on the earthquake size.

28. What is the disadvantage of the Richter scale?

The Richter scale does not work well for large or distant earthquakes.

29. What is the moment magnitude scale?

The moment magnitude scale estimates the total energy released by an earthquake.

30. In general, what value is used to define an earthquake as “small” on the moment magnitude scale?

Earthquakes below 5 are considered small on the scale.

31. How do geologists determine the epicenter of an earthquake?

Geologists use seismic waves to locate the epicenter of an earthquake.

32. Why are a minimum of three circles necessary to pinpoint the epicenter of an earthquake?

Geologists take data from seismographs in three different locations. Where the three circles meet is the epicenter of the quake.

Section 3

33. What is a seismograph? How does it work?

A Seismograph records seismic waves. Seismic waves cause the seismograph’s drum to vibrate.

34. What four devices are used in measuring fault movement?

The four devices used to measure fault movement include tilt meters, creep meters, laser-ranging devices, and GPS satellites

35. Describe the action of a creep meter.

A creep meter uses a wire stretched across a fault to measure horizontal movement of the ground. On one side of the fault a wire is attached to a post, on the other side the wire is attached to a weight that can slide if the fault moves.

36. Describe the action of laser ranging devices.

A laser beam is used to detect horizontal fault movement.

37. Describe the action of a tilt meter.

A tilt meter measures tilting or rising of the ground. It is similar to a carpenter’s level but it consists of two bulbs that are filled with liquid and connected by a hollow stem. The liquid will flow from one bulb to the other and the geologist will measure the liquid.

38. Describe how satellite monitors can measure earth movement

Geologists can monitor changes in elevation as well as horizontal movements along

faults using GPS. Geologists use the GPS to monitor markers on both sides of the fault.

Section 4

39. How do geologists determine earthquake risk?

Geologists can determine earthquake risk based on where faults are and where earthquakes have been in the past.

40. Examine the map of Pennsylvania and locate which areas have minor, moderate, and major risk of earthquakes.

Ramapo fault in eastern pa – Lancaster, Chester County

41. What section of the country has the greatest risk of earthquakes?

Western United States- California

42. What happens during liquefaction?

Liquefaction occurs when an earthquake’s violent shaking suddenly turns loose, soft soil into liquid mud.

43. What is an aftershock? An aftershock is an earthquake that occurs after a larger earthquake in the same area. When may they occur? An after shock can occur hours, days or months after the earthquake.

44. What are tsunamis? A tsunamis is generated when water displaced by an earthquake in the ocean floor.

45. How can we reduce earthquake damage?

To reduce earthquake damage buildings that are stronger and more flexible should be designed.

46. What is the best way to protect yourself in an earthquake?

The best way to protect yourself is drop, cover, and hold

47. Describe a base isolated building's movements in response to an earthquake.

A base isolated building rests on shock-absorbing rubber pads pr springs. During a quake the building moves gently back and forth without violent shaking

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