Earthquakes and Earth’s Interior Chapter 8 Earthquakes and Earth’s Interior

Chapter 8.1 Objectives Earthquakes Compare and Contrast the epicenter and focus of an earthquake Indentify the cause of earthquakes using the elastic rebound hypothesis. Explain what a fault is. Compare and contrast aftershocks and foreshocks.

6.1 What Is an Earthquake? Earthquakes earthquake vibration of Earth release of energy Focus Origin of Earthquake Epicenter Surface point directly above the focus Faults Fractures in E. where movement occurs

Focus, Epicenter, and Fault

Slippage Along a Fault

6.1 What Is an Earthquake? Cause of Earthquakes  Elastic Rebound Hypothesis rapid release of elastic energy stored in rock When strength of rock is exceeded it breaks Vibrations are caused by the break

Elastic Rebound Hypothesis

6.1 What Is an Earthquake? Cause of Earthquakes  Aftershocks and Foreshocks Aftershock _____________________ foreshock _______________________

Chapter 8.2 Objectives Measuring Quakes Identify 3 types of seismic waves and know how each moves. Explain how to locate the epicenter of an earthquake. Describe the different ways a Quake is measured. Know the difference between a seismograph and seismogram.

8.2 Measuring Earthquakes Earthquake Waves 8.2 Measuring Earthquakes  Seismographs -  Seismograms -

Seismograph

Seismogram

8.2 Measuring Earthquakes 3 types of Earthquake Waves 8.2 Measuring Earthquakes P waves - P - Travel through ________ ___________ & ___________ - Speed -__________________

8.2 Measuring Earthquakes Earthquake Waves 8.2 Measuring Earthquakes S waves Travel along outer surface - Shake particles - - Travel only through _____________ - Speed-

8.2 Measuring Earthquakes Types of Earthquake Waves 8.2 Measuring Earthquakes Surface waves are seismic waves that travel along Earth’s outer layer. A seismogram shows all three types of waves

Seismic Waves

8.2 Measuring Earthquakes Locating an Earthquake 8.2 Measuring Earthquakes Locating Epicenter Using the difference in the arrival times between P and S wave 3 seismographs are needed • About 95 percent of the major earthquakes occur in a few narrow zones.

Locating an Earthquake

8.2 Measuring Earthquakes Two factors— Intensity magnitude Richter Scale- NOT USED BY SCIENTISTS • Based on largest seismic wave • 32-fold energy increase per # • Not good for large earthquakes

8.2 Measuring Earthquakes  Momentum Magnitude Scale amount of displacement Surface Area of Fault Size of Wave Only scale that estimates total Amount of energy released • Measures very large earthquakes

Earthquake Magnitudes

Some Notable Earthquakes

Chapter 8.3 Objectives Measuring Quakes Describe 4 factors that contribute to earthquake destruction. Explain 3 other dangers associated with Earthquakes. Explain the potential for earthquake prediction & explain seismic gap. Be able to calculate the earthquake probability for various locations using the internet.

8.3 Destruction from Earthquakes Seismic Vibrations 8.3 Destruction from Earthquakes Damage depends on Intensity Duration material on which the structure is built design of structure unreinforced stone & brick are worst

Earthquake Damage

8.3 Destruction from Earthquakes Seismic Vibrations 8.3 Destruction from Earthquakes  Liquefaction • Saturated material turns fluid • Underground objects may float to surface

Effects of Subsidence Due to Liquefaction

Effects of Subsidence Due to Liquefaction

8.3 Destruction from Earthquakes Tsunamis 8.3 Destruction from Earthquakes  Cause of Tsunamis tsunami slab of the ocean floor is displaced vertically along a fault and wave results Can be caused by underwater landslide. • Tsunami is the Japanese word for “seismic sea wave.”

Movement of a Tsunami

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

8.3 Destruction from Earthquakes Other Dangers 8.3 Destruction from Earthquakes Landslides Greatest damage Ground Subsidence Sinking of ground Caused by vibrations Fire San Francisco 1906 Gas, electrical, water lines severed

Landslide Damage

8.3 Destruction from Earthquakes Predicting Earthquakes 8.3 Destruction from Earthquakes  Short-Range Predictions • Not yet possible  Long-Range Forecasts • NO predictions, only probabilities seismic gap where there has not been any earthquake activity for a long period of time.

Earth’s Layers List the 3 main layers of earth based on composition. Chapter 8.4 Objectives Earth’s Layers List the 3 main layers of earth based on composition. List & describe 5 layers of the Earth based on physical properties. Explain how Earthquakes help us understand the Earth’s layers.

8.4 Earth’s Layered Structure Layers Defined by Composition 8.4 Earth’s Layered Structure  Three major zones  Crust • Thin, rocky outer layer • thickness varies - 7 km in oceanic - 8–40 km continental - Exceeds 70 km in mountain

8.4 Earth’s Layered Structure Layers Defined by Composition 8.4 Earth’s Layered Structure  Crust cont. • Continental crust - Upper - granitic rocks - Lower - basaltic - density is about 2.7 g/cm3 - Up to 4 billion years old

8.4 Earth’s Layered Structure Layers Defined by Composition 8.4 Earth’s Layered Structure  Crust cont. • Oceanic crust - Basaltic composition - Density about 3.0 g/cm3 - Younger (<180 million yrs)

Seismic Waves Paths Through the Earth animation

8.4 Earth’s Layered Structure Layers Defined by Composition 8.4 Earth’s Layered Structure  Mantle Below crust to a depth of 2900 kilometers Composition Upper mantle - peridiotite

8.4 Earth’s Layered Structure Layers Defined by Composition 8.4 Earth’s Layered Structure  Core • Below mantle • Sphere with a radius of 3486 kilometers • Composed of an iron-nickel alloy • Average density of nearly 11 g/cm3

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

8.4 Earth’s Layered Structure Layers Defined by Physical Properties 8.4 Earth’s Layered Structure  Lower Mantle • 660–2900 km • More rigid layer • Rocks are very hot and capable of gradual flow.

8.4 Earth’s Layered Structure Layers Defined by Physical Properties 8.4 Earth’s Layered Structure  Inner Core • Sphere with a radius of 1216 km • Behaves like a solid  Outer Core • Liquid layer • 2270 km thick • Convective flow of metallic iron within generates Earth’s magnetic field

Earth’s Layered Structure

8.4 Earth’s Layered Structure Discovering Earth’s Layers 8.4 Earth’s Layered Structure  Moho ˇ ´ • 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 explained if Earth contains a core composed of materials unlike the overlying mantle

Earth’s Interior Showing P and S Wave Paths

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

8.4 Earth’s Layered Structure 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.