Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Seismic Waves When rock under Earth’s surface moves or breaks, energy travels in the form of seismic waves, which cause the ground to shake and vibrate—an earthquake. Study of seismic waves has led scientists to understand that Earth is a layered planet consisting of: Crust Mantle Outer core Inner core

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Seismic Waves-Body Waves Two main types of seismic waves: Body waves travel through Earth’s interior —Primary waves (P-waves) —Secondary waves (S-waves)

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Primary Waves: Longitudinal motion: —compress and expand the material through which they move. —occurs parallel to the wave’s direction of travel. Travel through any type of material—solid rock, magma, water, or air Fastest of all seismic waves—first to register on a seismograph.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Secondary Waves: Transverse: —Vibrate the rock in an up-and-down or side-to-side motion. —Occurs perpendicular to a wave’s direction of travel. Travel through solids—unable to move through liquids. Slower than P-waves—second to register on a seismograph.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Surface Waves: Slowest seismic waves and the last to register on a seismograph. –Rayleigh waves have a rolling-type of motion: (similar to ocean wave movement) Ground moves up and down. –Love waves have similar motion to S-waves: Horizontal surface motion (side to side)

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Abrupt changes in seismic-wave velocity reveal boundaries between different materials within the Earth. The densities of the different layers can be estimated by studying the various seismic- wave velocities.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Discovery: Crust–Mantle Boundary In 1909, Andrija Mohorovicic had observed a sharp increase in seismic velocity at a shallow layer within Earth. Discovered the crust–mantle boundary. ˇ ´

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Discovery: Mantle-Core Boundary Richard Oldham observed that P-waves and S-waves travel together for a distance, then encounter a boundary where the S-waves stop and the P-waves refract.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Mantle-Core Boundary In 1913, Beno Guttenberg refined Oldham’s work by locating the depth of the core-mantle boundary (2900 km). P-wave shadow (where no waves are detected) over part of the Earth.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Interpreting the Core-Mantle Boundary In 1926 Sir Harold Jeffries determined that part of the core must be liquid.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Earth’s Internal Layers: Inner Core-Outer Core In 1936, Lehmann observed that P- waves also refract at a certain depth within the core. –At this depth, P- waves show an increase in velocity, indicating higher density material. Lehmann discovered the two parts: a liquid outer core and a solid inner core.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Putting it together: The discoveries of everyone indicate that Earth is composed of three layers of different compositions: the crust, mantle, and core.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Crust: Oceanic crust –compact (10 kilometers in thickness) —Composed of mafic rocks. Continental crust (20 and 60 kilometers) –Composed of felsic rocks. Low-density crust floats on the denser, underlying mantle

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Why are continents high and oceans low? Isostasy! Areas of continental crust stand higher because it is thicker and less dense than oceanic crust.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Mantle: 82% of Earth’s volume/65% of Earth’s mass. Earth’s thickest layer—2900 km Rich in silicon and oxygen. —Some iron, magnesium, and calcium. Divided into two regions—upper mantle and lower mantle.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The upper mantle has two zones: Lithosphere - the uppermost plus the crust. –cool and rigid. —does not flow but rides atop the lower portion Broken up into individual plates. Movement of lithospheric plates causes earthquakes, volcanic activity, and mountain building.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The upper mantle has two zones: Lower part-the asthenosphere. –behaves in a plastic- like manner, allowing it to flow easily. The constant flowing motion greatly affects the surface features of the crust.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Lower Mantle: Extends from a depth of 700 kilometers to the outer core. Under great pressure the rock is solid.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Core: Composed predominantly of metallic iron. 2 layers—a solid inner core; liquid outer core. –The inner core is solid due to great pressure. –The outer core is under less pressure and flows in a liquid phase. Earth’s magnetic field generating flowing molten core.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Earthquakes Can occur on or between plate boundaries. Strain begins at depth as elastic deformation. When the build-up of stress exceeds the rock’s elastic limit, the rock breaks. This is how a fault forms.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley There are three type of stress caused by interactions between plate boundaries: Compressional stress—slabs pushed together Tensional stress—slabs pulled apart Shear stress—slabs are both pulled and pushed—sliding

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Continental Evidence for Plate Tectonics: Faults Classified by relative direction of movement (displacement). –Footwall –Hanging wall

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Continental Evidence for Plate Tectonics: Faults In a normal fault, the hanging wall drops down relative to the level of the footwall.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Continental Evidence for Plate Tectonics: Faults A reverse fault occurs when the hanging wall is pushed up relative to the footwall.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Continental Evidence for Plate Tectonics: Faults In a strike-slip fault, blocks of rock slip past one another with very little vertical displacement. (The San Andreas Fault is a strike-slip fault)

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Earthquake Measurement The Richter scale measures the energy released in terms of ground shaking. Each increase of one unit on the scale is a ten-fold increase in amplitude.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Tsunami A giant sea wave, or series of sea waves, generated by a powerful disturbance that vertically displaces the water column. Reverse fault earthquakes thrust the seafloor upward. Huge, displaced mass of water drops back down to sea level and a large wave is generated.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Continental Evidence for Plate Tectonics Rocks respond to stress in 3 ways: Elastic deformation—returning to original shape Brittle deformation—breaking Plastic deformation—flowing

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Continental Evidence for Plate Tectonics: Folds Syncline: Layers tilt in toward a fold axis. Anticline: Layers tilt away from axis.