Post on 16-Dec-2015
Earth ScienceEarth Science
Chapter 4Chapter 4
The Dynamic CrustThe Dynamic Crust
Earth’s Crust and InteriorEarth’s Crust and Interior
• Earthquake waves help determine properties of Earth’s interior such as:– thickness– composition – temperature – density– pressure
Earth’s Crust and InteriorEarth’s Crust and Interior
• The speed of earthquake waves change abruptly at the interfaces between layers of the Earth.– Waves speed up due to increasing density.– Example: speed increases at the interface
between the crust and asthenosphere.• This interface is the Mohorovicic
discontinuity, or “Moho” interface.
EarthquakesEarthquakes
• An earthquake is the shaking of Earth’s crust caused by rapid moving of rocks. – Point beneath Earth’s surface where an
earthquake originates is the focus– Point on Earth’s surface directly above the
focus is called the epicenter
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EarthquakesEarthquakes
• When an earthquake occurs, it generates energy waves, called seismic waves.– Seismograph – instrument used to
detect and record earthquake waves
– Seismogram –recording of earthquake waves
EarthquakesEarthquakes
• Main types of earthquake waves:– P-waves (primary waves)
• Particles vibrate in same direction as wave• Travel fast through solids, liquids & gasses
– S-waves (secondary waves)• Particles vibrate at right angles to wave• Travel slower than p-waves• Only travel through solids
EarthquakesEarthquakes
• Since the outer core is liquid, S-waves do not travel through it and P-waves refract. – This results in a shadow zone where no
seismic waves are received.
EarthquakesEarthquakes
• P-waves travel fast and arrive at a seismic station ahead of S-waves.
• The difference in travel times can be used to determine the distance from a seismograph station to the epicenter of an earthquake.
EarthquakesEarthquakes
EarthquakesEarthquakes
• To determine the exact epicenter data from three seismic stations must be used to construct three circles of possible locations.
• The point where all three circles intersect is the epicenter.
EarthquakesEarthquakes
EarthquakesEarthquakes
• The intensity and energy of an earthquake are measured on two different scales.– Richter Scale – measure of energy released
• Scale from 1 to 10 • Each step increases 10 times in magnitude
– Modified Mercalli Scale – measure of effect• Scale uses Roman numerals from I to XII • Higher numbers indicate greater damage
Evidence for Crustal MovementEvidence for Crustal Movement
• Zones of frequent crustal activity can be located on the Earth’s surface.
• Most earthquakes, volcanoes, ridges, trenches, and mountains occur here.
Evidence for Crustal MovementEvidence for Crustal Movement
• Continental Drift– Continental land masses have been moving
across the Earth’s surface for millions of years– Evidence supporting continental drift
• Continents look like they fit together• Similar rocks, minerals, and fossils are
found on different continents in areas that look like they once fit together.
Evidence for Crustal MovementEvidence for Crustal Movement
Evidence for Crustal MovementEvidence for Crustal Movement
Evidence for Crustal MovementEvidence for Crustal Movement
Evidence for Crustal MovementEvidence for Crustal Movement
• Plate Tectonics – Earth’s crust is divided into several sections
(plates) that move across Earth’s surface.
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Evidence for Crustal MovementEvidence for Crustal Movement6 min video
• Plates move due to convection cells produced by unequal heating of the fluids within the asthenosphere.
Evidence for Crustal MovementEvidence for Crustal Movement
• There are three types of plate interactions– Divergent boundaries– Convergent boundaries– Transform boundaries
Evidence for Crustal MovementEvidence for Crustal Movement
• Divergent Boundaries– Plates move apart from each other– New crust is formed here – Most commonly found at mid-ocean ridges
and develop deep rift valleys.
Evidence for Crustal MovementEvidence for Crustal Movement
• Convergent Boundaries– Plates move toward each other– When 2 continental plates meet mountains
are formed.• Himalayan Mountains formed like this
Evidence for Crustal MovementEvidence for Crustal Movement
– When an ocean plate and a continental plate converge subduction occurs. • Denser ocean plate slides under the less
dense continental plate.
• Ocean trench develops at point of subduction.• Volcanoes and mountains form along the
edge of the continental plate.
Evidence for Crustal MovementEvidence for Crustal Movement
• Transform Boundaries– Plates slide horizontally past one another– Tension builds as plates slide and when
tension is released earthquakes occur.• San Andreas Fault is an example
Evidence for Crustal MovementEvidence for Crustal Movement
Evidence for Crustal MovementEvidence for Crustal Movement
• The ocean floor appears to be spreading based on two major pieces of evidence.
1. The age of igneous rocks increases as the distance from the mid-ocean ridges increases.
2. Parallel strips of igneous rocks on either side of the mid ocean ridge show periodic reversals of magnetic polarity.
Evidence for Crustal MovementEvidence for Crustal Movement
Evidence for Crustal MovementEvidence for Crustal Movement
• Deformed rock strata– Sedimentary rocks normally form in horizontal
layers.– Sedimentary layers that are not horizontal
provides evidence of change.
Evidence for Crustal MovementEvidence for Crustal Movement
Syncline Anticline
Evidence for Crustal MovementEvidence for Crustal Movement
• Displaced rock strata occurs along faults (cracks in rock formations).– The 3 types of faults are:
• Normal• Reverse• Transform or strike-slip
Evidence for Crustal MovementEvidence for Crustal Movement
Normal Fault
Evidence for Crustal MovementEvidence for Crustal Movement
Reverse Fault
Evidence for Crustal MovementEvidence for Crustal Movement
Transform or Strike-slip Fault
Evidence for Crustal MovementEvidence for Crustal Movement
• Displaced marine fossils are sometimes found high up in the mountains.
• Benchmarks labeled with date and elevation are set into ground and checked periodically.