1. Chapter 8 Earthquakes and Earth’s Interior

2. Think-Pair-Share Read the following questions and discuss possible answers with the person you are sitting next to to review today’s concepts. 1)What makes the earth move in an earthquake? 2) Are earthquakes possible anywhere? Why or why not? 3) Are earthquakes always dangerous? Explain your reasoning.

3. Today’s Objective Create a model of 3 types of faults & use your model to investigate what happens on Earth during each type of fault movement. Vocab: Normal Fault, Thrust Fault, Strike- Slip Fault

4. What Does This Map Show? The Ring of Fire is a large area surrounding the Pacific Ocean that is prone to earthquakes and volcanoes due to plate boundaries (converging with each other).

5. What is an Earthquake? An Earthquake is the vibration of Earth produced by the rapid release of energy, often caused by slippage along a break in Earth’s crust. These breaks are called Faults.

6. How Often do Earthquakes Occur? Out of all the earthquakes about 30,000 occur worldwide that are strong enough to be felt. Of these, only about 75 are considered major earthquakes. About 1 Million Earthquakes occur each year!

7. Focus and Epicenter The point within Earth where an earthquake starts is called the focus. The epicenter is the location on the surface directly above the focus.

8. Faults Faults are fractures in Earth where movement has occurred.

9. Types of Faults * Reverse Faults and Also Known as Thrust Faults

10. Normal Fault

11. Reverse (Thrust) Fault

12. Strike-Slip Fault

13. What Causes an Earthquake? The Elastic Rebound Theory: When rocks push against each other at a fault energy is built up and the rocks are deformed and bend like a stick when it’s bent. When the rocks slip at a weak point they will spring back into their original place. This process releases LOTS of energy (vibrations) in the form of an earthquake. –(There is a diagram of this process on page 220 of your textbook.)

14. Elastic Rebound Theory

15. Types of Earthquake Waves P-Waves are primary, or compression waves. They will always arrive first. They are “push-pull” waves. S-Waves are secondary, or transverse waves and shake particles at right angles to their direction of travel.

16. Surface Waves Surface Waves are seismic waves that travel along Earth’s outer layer. Move up and down and side to side. (much like ocean waves tossing a ship)

17. Aftershocks and Foreshocks Aftershocks are movements, or smaller earthquakes in the Earth that follow a major earthquake. Foreshocks are small earthquakes that come before a major earthquake.

18. Measuring Earthquakes Seismographs are instruments that record earthquake waves.

19. Measuring Earthquakes The Richter Scale: Measures Amplitude of largest waves

20. Measuring Earthquakes The Mercalli Scale- measures earthquake damage and intensity.

21. P-S Wave Travel Times P-Wave S-Wave

22. Locating The Epicenter Triangulation. Three seismic stations are needed to locate the epicenter of an earthquake:

23. Article: Giant Earthquakes off Sumatra 1) Explain the magnitude and damage done by the 2004 earthquake. 2) Where was the location of the fault? 3) Explain what “micro-atolls” are and how they are used to look for patterns in earthquake activity. 4) What is the pattern scientists discovered? 5) What are scientists predicting about the current cycle? 6) Are the people in the area more or less prepared today? Explain.

24. Where are Earthquake Zones? 95% of Earthquakes occur in a few narrow zones, mostly around the outer edge of the Pacific ocean. Another zone is along the Mediterranean Sea.

25. Review Questions What are the three types of faults? What are the three types of earthquake waves? What do we call smaller earthquakes that follow a major earthquake? Can you name 2 earthquake rating scales? What is triangulation? What is a P-S travel time graph?

26. Steps for 1 st page 1)Convert P-Wave arrival time into seconds. Ex. 3 min 20 sec = 200 sec. 2)To figure out the Distance to Epicenter Multiply the P-Wave arrival time by 6. ex. 200 x 6 = 1200 km. Repeat for all 5 cities. 3)Divide distance from epicenter by 325. ex: 1200/325 = 3.7 cm (this is the radius of the circle you will draw on the map. 4)Draw circle on your map using a compass using the radius you calculated in step #3.

27. Earthquake Damage Unconsolidated sediments may undergo liquefaction in a strong earthquake allowing buildings to sink, usually one side more than the other so that the building topples.

28. Earthquake Damage - Strong earthquakes typically break underground gas lines leading to fires. Water lines also break making it difficult to fight the fires. - Strong earthquakes that offset the seafloor produce tsunamis, which are not normally discernible from a ship at sea with their very long wavelengths, but as theses very rapidly moving waves come into shallow water approaching the shoreline they slow greatly, getting steeper and much higher innundating low-lying coasts. - Earthquakes may also set landslides and mudslides in motion, burying whole neighborhoods.

29. Liquefaction Example

30. Landslides The violent shaking of an earthquake can cause the soil and rock on slopes to fail, resulting in a landslide.

31. Mudslides

32. Tsunamis A tsunami is a seismic sea wave A tsunami is triggered by an earthquake where a slab of ocean floor is displaced vertically along a fault.

33. Predicting Earthquakes Short Range predictions, scientists try to measure: –Uplift, subsidence & strain of rocks near faults –Water levels and pressure in wells –Radon gas emissions from fractures –Electromagnetic properties of rocks –So far short range predicting has not been successful

34. Long Range Predicting In long range predicting scientists give the probability of an earthquake occurring within a 30-100 years time frame. Long range predicting is based on the idea that earthquakes in certain areas are repetitive Scientists also study Seismic Gaps: areas where there has not been earthquake activity for a long time.

35. Earth’s Layers

36. Layers of the Earth Crust- Earth’s rocky outer layer. Average thickness is 40 KM. Average rock is granitic. Mantle- Over 82% of Earth’s volume is in the mantle. There is an upper mantle which is flexible and lower mantle which is rigid. Extends to a depth of 2890 KM. Core- Composed of iron-nickel. The outer core is liquid & 2260 KM thick & generates Earth’s magnetic field. The inner core is solid because of immense pressure and has a radius of 1220 KM.

37. Earth’s Layers Lithosphere= crust & upper mantle aka “Sphere of Rock” Aesthenosphere= weak layer below the lithosphere…upper mantle

39. Discovering Earth’s Layers The Moho is the boundary layer between the Earth’s crust and mantle. Seismic waves travel faster here. Seismic waves travel through the Earth. P waves can travel through Earth’s liquid core, while S waves cannot. The “Shadow Zone” is an area where P waves are bent when traveling through the liquid outer core from an area between 100 & 140 degrees away from an earthquake’s epicenter.

40. 100-140 degrees Epicenter

41. Earthquake Building Scoring Earthquake Building Design Rubric Building design is realistic, innovative & creative, teamwork was evident. 12345 Building is sturdy, one floor holds sandbag (bonus pts if both floors can hold sandbag) 12345 Building met building guidelines: (2 stories tall, each story at least 18 cm high 12345 Building survives moderate sized earthquake on shake table 12345 * Points taken off if extra materials are needed