Earth's Interior Notes

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Prentice Hall EARTH SCIENCE : 

Prentice Hall EARTH SCIENCE Tarbuck Lutgens 

Chapter 8 : 

Chapter 8 Earthquakes and Earth’s Interior

8.4 Earth’s Layered Structure : 

8.4 Earth’s Layered Structure Seismic waves change speed as they pass through earth. Increased density w/ depth Waves bounce, bend, etc.

Seismic Waves Paths Through the Earth : 

Seismic Waves Paths Through the Earth

8.4 Earth’s Layered Structure : 

8.4 Earth’s Layered Structure  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

8.4 Earth’s Layered Structure : 

8.4 Earth’s Layered Structure Layers Defined by Composition Crust Continental Crust  Crust • Continental crust - Upper crust composed of granitic rocks - Lower crust is more akin to basalt - Average density is about 2.7 g/cm3 - Up to 4 billion years old Layers Defined by Composition

8.4 Earth’s Layered Structure : 

8.4 Earth’s Layered Structure

8.4 Earth’s Layered Structure : 

8.4 Earth’s Layered Structure  Crust • Oceanic crust - Basaltic composition - Density about 3.0 g/cm3 - Younger (180 million years or less) than the continental crust

8.4 Earth’s Layered Structure : 

8.4 Earth’s Layered Structure  Mantle • Majority (82%) of earth’s volume • Composition of the uppermost mantle is the igneous rock peridotite (changes at greater depths). Below crust to a depth of 2900 kilometers

8.4 Earth’s Layered Structure : 

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 : 

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 “putty”

8.4 Earth’s Layered Structure : 

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 : 

8.4 Earth’s Layered Structure

Earth’s Layered Structure : 

Earth’s Layered Structure

8.4 Earth’s Layered Structure : 

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 explained if Earth contains a core composed of materials unlike the overlying mantle  Moho

Earth’s Interior Showing P and S Wave Paths : 

Earth’s Interior Showing P and S Wave Paths

8.4 Earth’s Layered Structure : 

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. Seismic waves pass the same way through “sample” rocks heated and squeezed in lab.

8.4 Earth’s Layered Structure : 

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. • Nebular cloud Nuclear Fusion Density floating materials into layers From former planets/stars??? Meteorites, too!  Origin of materials

9.5 Mechanisms of Plate Motion : 

9.5 Mechanisms of Plate Motion  Heat Energy Transfer Radiation – as a wave Conduction – through direct contact Convection – circulation of a fluid due to uneven heating

9.5 Mechanisms of Plate Motion : 

9.5 Mechanisms of Plate Motion  Scientists generally agree that convection occurring in the mantle is the basic driving force for plate movement. Convective flow is the motion of matter resulting from changes in temperature. Heat Source – Radiation and Core Heat Plates – Cool, top parts of convection current

9.5 Mechanisms of Plate Motion : 

9.5 Mechanisms of Plate Motion  Subduction Zone Low Density vs. High Density Continental vs. Oceanic

9.5 Mechanisms of Plate Motion : 

9.5 Mechanisms of Plate Motion  Slab-Pull and Ridge-Push Ridge-push causes oceanic lithosphere to slide down the sides of the oceanic ridge under the pull of gravity. It may contribute to plate motion. Slab-pull is a mechanism that contributes to plate motion in which cool, dense oceanic crust sinks into the mantle and “pulls” the trailing lithosphere along. It is thought to be the primary downward arm of convective flow in the mantle.

9.5 Mechanisms of Plate Motion : 

9.5 Mechanisms of Plate Motion  Mantle Convection The unequal distribution of heat within Earth causes the thermal convection in the mantle that ultimately drives plate motion. Mantle plumes are masses of hotter-than-normal mantle material that ascend toward the surface, where they may lead to igneous activity.

8.1 What Is an Earthquake? : 

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.  An earthquake is the vibration of Earth produced by the rapid release of energy  Focus and Epicenter • Faults are fractures in Earth where movement has occurred.  Faults

Focus, Epicenter, and Fault : 

Focus, Epicenter, and Fault

8.1 What Is an Earthquake? : 

8.1 What Is an Earthquake? • Horizontal: offset or displaced fault Vertical: uplifted fault  Large (meters) movement

Slippage Along a Fault : 

Slippage Along a Fault

8.1 What Is an Earthquake? : 

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 forces. • When the strength of the rock is exceeded, it suddenly breaks, causing the vibrations of an earthquake.

Elastic Rebound Hypothesis : 

Elastic Rebound Hypothesis

8.1 What Is an Earthquake? : 

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

8.2 Measuring Earthquakes : 

8.2 Measuring Earthquakes  Seismographs are instruments that record earthquake waves.  Seismograms are traces of amplified, electronically recorded ground motion made by seismographs.

Seismograph : 

Seismograph

Seismogram : 

Seismogram

8.2 Measuring Earthquakes : 

8.2 Measuring Earthquakes  Surface waves are seismic waves that travel along Earth’s outer layer. Move both vertically and horizontally Most significant damage to humans

8.2 Measuring Earthquakes : 

8.2 Measuring Earthquakes  Body Waves – pass through interior • P waves • Identified as P waves or S waves - Have the greatest velocity of all earthquake waves - Are push-pull waves that push (compress) and pull (expand) in the direction that the waves travel (longitudinal/compressional) - Travel through solids, liquids, and gases

8.2 Measuring Earthquakes : 

8.2 Measuring Earthquakes  Body Waves • S waves Seismic waves that travel along Earth’s outer layer - Slower velocity than P waves - Shake particles at right angles to the direction that they travel (transverse) - Travel only through solids  A seismogram shows all three types of seismic waves—surface waves, P waves, and S waves.

Seismic Waves : 

Seismic Waves

8.2 Measuring Earthquakes : 

8.2 Measuring Earthquakes  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, which are related to distance. • About 95 percent of the major earthquakes occur in a few narrow zones.  Earthquake Direction  Earthquake Zones

Locating an Earthquake : 

Locating an Earthquake

8.2 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

8.2 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 : 

Earthquake Magnitudes

Some Notable Earthquakes : 

Some Notable Earthquakes

8.3 Destruction from Earthquakes : 

8.3 Destruction from Earthquakes  The damage to buildings and other structures from earthquake waves depends on several factors. These factors include the 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 : 

Earthquake Damage

8.3 Destruction from Earthquakes : 

8.3 Destruction from Earthquakes  Building Design - The design of the structure - Unreinforced stone or brick buildings are the most serious safety threats - Nature of the material upon which the structure rests • Factors that determine structural damage - Intensity of the earthquake

8.3 Destruction from Earthquakes : 

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 : 

8.3 Destruction from Earthquakes  Cause of Tsunamis • A tsunami triggered by an earthquake occurs where a slab of the ocean floor is displaced vertically along a fault. • 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 : 

Movement of a Tsunami

8.3 Destruction from Earthquakes : 

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.

8.3 Destruction from Earthquakes : 

8.3 Destruction from Earthquakes • With many earthquakes, the greatest damage to structures is from landslides and ground subsidence, or the sinking of the ground triggered by vibrations.  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.  Fire

Landslide Damage : 

Landslide Damage

8.3 Destruction from 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.

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