EARTH SCIENCE Prentice Hall EARTH SCIENCE Tarbuck Lutgens 

8 Chapter 8 Earthquakes and Earth ’ s Interior In your notebook’s glossary, define: 1. earthquake 2. fault 3. focus 4. epicenter 5. seismic waves 6. P waves 7. S waves 8. surface waves 9. seismograph 10. tsunami 11. seismic gap 12. crust 13. mantle 14. core 15. lithosphere 16. asthenosphere 17. outer core 18. inner core DUE NEXT CLASS (Mon./Tues.) VOCAB. QUIZ after that (Wed./Thurs.)

8 Chapter 8 Earthquakes and Earth ’ s Interior R: An earthquake is the vibration of Earth produced by the rapid release of energy. L: 1. Where does the energy come from? L: 2. What types of vibrations/waves carry this energy?

Earthquakes 8.1 What Is an Earthquake? Focus is the point within Earth where the earthquake starts. Epicenter is the location on the surface directly above the focus.  Focus and Epicenter Faults are fractures in Earth where movement has occurred.  Faults

Draw this under questions on left: Focus, Epicenter, and Fault

Slippage Along a Fault

Cause of Earthquakes 8.1 What Is an Earthquake?  Elastic Rebound Hypothesis Most earthquakes are produced by the rapid release of elastic energy stored in rock that has been subjected to great tectonic forces. When the strength of the rock is exceeded, it suddenly breaks, causing the vibrations of an earthquake.

Elastic Rebound Hypothesis

Cause of Earthquakes 8.1 What Is an Earthquake? An aftershock is a small earthquake that follows the main earthquake. A foreshock is a small earthquake that often precedes a major earthquake.  Aftershocks and Foreshocks

Earthquake Waves 8.2 Measuring Earthquakes  Seismographs are instruments that record earthquake waves.  Surface waves are seismic waves that travel along Earth’s outer layer.  Seismograms are traces of amplified, electronically recorded ground motion made by seismographs.

Seismograph

Seismogram

I. Earthquake Waves 8.2 Measuring Earthquakes A. Body Waves 1. P waves (P waves and S waves). c. Have the greatest velocity of all earthquake waves a. Are push-pull waves that push (compress) and pull (expand) in the direction that the waves travel b. Travel through solids, liquids, and gases

Earthquake Waves 8.2 Measuring Earthquakes  Body Waves 2. S waves a. Seismic waves that travel along Earth’s outer layer d. Slower than P waves b. Shake particles at right angles to the direction that they travel c. Travel only through solids  A seismogram shows all three types of seismic waves—surface waves, P waves, and S waves.

Seismic Waves Now answer question 2! B. Surface waves occur when energy reaches surface and makes ground “roll” and shake.

II. Locating an Earthquake 8.2 Measuring Earthquakes A. Earthquake Distance Travel-time graphs from three or more seismographs can be used to find the exact location of an earthquake epicenter. The epicenter is located using the difference in the arrival times between P and S wave recordings. About 95 percent of the major earthquakes occur in a few narrow zones. B. Earthquake Direction C. Earthquake Zones

Locating an Earthquake Next left page: Fig 8 p How far is the station from the epicenter? 2.What is the difference in travel time if the station is 2000km from epicenter?

Measuring Earthquakes 8.2 Measuring Earthquakes  Historically, scientists have used two different types of measurements to describe the size of an earthquake —intensity and magnitude.  Richter Scale Does not estimate adequately the size of very large earthquakes Based on the amplitude of the largest seismic wave Each unit of Richter magnitude equates to roughly a 32-fold energy increase

Measuring Earthquakes 8.2 Measuring Earthquakes  Momentum Magnitude Derived from the amount of displacement that occurs along the fault zone Moment magnitude is the most widely used measurement for earthquakes because it is the only magnitude scale that estimates the energy released by earthquakes. Measures very large earthquakes

Earthquake Magnitudes L: Table 1 p.225: 1. What range of magnitudes are rarely felt? 2. How many major earthquakes occur per year on Earth on average?

Some Notable Earthquakes L: p Where was the greatest North American quake? 2. What caused extensive damage from the 1906 S.F. earthquake? 3. What was the magnitude of the 1989 “Bay area” earthquake?

Seismic Vibrations 8.3 Destruction from Earthquakes  The direct damage to buildings and structures from earthquake waves depends on several factors: intensity and duration of the vibrations, the nature of the material on which the structure is built, and the design of the structure.

Earthquake Damage

Seismic Vibrations 8.3 Destruction from Earthquakes  Building Design B. Unreinforced stone or brick buildings are the most serious safety threats C. Nature of the material upon which the structure rests III. Factors that determine structural damage A. Intensity of the earthquake

IV. Other hazards from earthquakes 8.3 Destruction from Earthquakes A. Liquefaction Saturated “solid” material turns fluid Underground objects may float to surface

Effects of Subsidence Due to Liquefaction

Tsunamis 8.3 Destruction from Earthquakes  Cause of Tsunamis B. A tsunami triggered by an earthquake when: 1. a slab of the ocean floor is displaced vertically along a fault, or 2. A tsunami also can occur when the vibration of a quake sets an underwater landslide into motion. Tsunami is the Japanese word for “seismic sea wave.”

Movement of a Tsunami

Tsunamis 8.3 Destruction from Earthquakes Large earthquakes are reported to Hawaii from Pacific seismic stations.  Tsunami Warning System Although tsunamis travel quickly, there is sufficient time to evacuate all but the area closest to the epicenter.

Other Dangers 8.3 Destruction from Earthquakes With many earthquakes, the greatest damage to structures is from landslides and ground subsidence (the sinking of the ground, triggered by vibrations) C. Landslides In the San Francisco earthquake of 1906, most of the destruction was caused by fires that started when gas and electrical lines were cut. D. Fire

Landslide Damage

Predicting Earthquakes 8.3 Destruction from Earthquakes So far, methods for short-range predictions of earthquakes have not been successful.  Short-Range Predictions Scientists don’t yet understand enough about how and where earthquakes will occur to make accurate long-term predictions.  Long-Range Forecasts A seismic gap is an area along a fault where there has not been any earthquake activity for a long period of time.

Layers Defined by Composition 8.4 Earth’s Layered Structure Draw and label Fig 16 from p. 234!  Earth’s interior consists of three major zones defined by their chemical composition—the crust, mantle, and core. Thin, rocky outer layer  Crust Varies in thickness - Roughly 7 km in oceanic regions - Continental crust averages 8–40 km - Exceeds 70 km in mountainous regions

Seismic Waves Paths Through the Earth

V. Layers Defined by Composition 8.4 Earth’s Layered Structure A. Crust 1. Continental crust a. Upper crust composed of granitic rocks - Lower crust is more akin to basalt b. Average density is about 2.7 g/cm 3 c. Up to 4 billion years old d. Thickness ranges from 8 km (ocean basins) to 70 km (folded mountains)

Layers Defined by Composition 8.4 Earth’s Layered Structure  Crust 2. Oceanic crust a. Basaltic composition b. Density about 3.0 g/cm 3 c. Younger (180 million years or less) than the continental crust d. Thin (~7km)

Layers Defined by Composition 8.4 Earth’s Layered Structure B. Mantle (Below crust to a depth of 2900 kilometers) Composition of the uppermost mantle is the igneous rock peridotite (changes at greater depths).

Layers Defined by Composition 8.4 Earth’s Layered Structure C. Core 1. Below mantle Sphere with a radius of 3486 kilometers 2. Composed of an iron-nickel alloy 3. Average density of nearly 11 g/cm 3 Mr. Lee Layers of the Earth:

VI. Layers Defined by Physical Properties 8.4 Earth’s Layered Structure A. Lithosphere 1. Crust and uppermost mantle (about 100 km thick) 2. Cool, rigid, solid B. Asthenosphere 1. Beneath the lithosphere 2. Upper mantle 3. To a depth of about 660 kilometers 4. Soft, weak layer that is easily deformed

Layers Defined by Physical Properties 8.4 Earth’s Layered Structure C. Lower Mantle –2900 km 2. More rigid layer 3. Rocks are very hot and capable of gradual flow.

Layers Defined by Physical Properties 8.4 Earth’s Layered Structure D. Outer Core 1. Liquid layer km thick 3. Convective flow of metallic iron within generates Earth’s magnetic field Simulation video:

Layers Defined by Physical Properties 8.4 Earth’s Layered Structure E. Inner Core 1. Sphere with a radius of 1216 km 2. Behaves like a solid

Earth’s Layered Structure 3 Compositional layers 5 Physical layers Complete flow chart from p.233 of book in your NB.

Discovering Earth’s Layers 8.4 Earth’s Layered Structure Velocity of seismic waves increases abruptly below 50 km of depth Separates crust from underlying mantle  Shadow Zone Absence of P waves from about 105 degrees to 140 degrees around the globe from an earthquake Can be e xplained if Earth contains a core composed of materials unlike the overlying mantle  Moho ˇ ´

Earth’s Interior Showing P and S Wave Paths

Discovering Earth’s Composition 8.4 Earth’s Layered Structure  Mantle  Crust Early seismic data and drilling technology indicate that the continental crust is mostly made of lighter, granitic rocks. Composition is more speculative. Some of the lava that reaches Earth’s surface comes from asthenosphere within.

Discovering Earth’s Composition 8.4 Earth’s Layered Structure  Core Earth’s core is thought to be mainly dense iron and nickel, similar to metallic meteorites. The surrounding mantle is believed to be composed of rocks similar to stony meteorites.