Presentation on theme: "Chapter 4 The Dynamic Crust"— Presentation transcript:
1Chapter 4 The Dynamic Crust Earth ScienceChapter 4The Dynamic Crust
2Earth’s Crust and Interior Earthquake waves help determine properties of Earth’s interior such as:thicknesscompositiontemperaturedensitypressure
3Earth’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.
4EarthquakesAn 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 focusPoint on Earth’s surface directly above the focus is called the epicenter2
5EarthquakesWhen an earthquake occurs, it generates energy waves, called seismic waves.Seismograph – instrument used to detect and record earthquake wavesSeismogram –recording of earthquake waves
6Earthquakes Main types of earthquake waves: P-waves (primary waves) Particles vibrate in same direction as waveTravel fast through solids, liquids & gassesS-waves (secondary waves)Particles vibrate at right angles to waveTravel slower than p-wavesOnly travel through solids
7EarthquakesSince 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.
8EarthquakesP-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.
10EarthquakesTo 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.
12EarthquakesThe intensity and energy of an earthquake are measured on two different scales.Richter Scale – measure of energy releasedScale from 1 to 10Each step increases 10 times in magnitudeModified Mercalli Scale – measure of effectScale uses Roman numerals from I to XIIHigher numbers indicate greater damage
13Evidence 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.
14Evidence for Crustal Movement Continental DriftContinental land masses have been moving across the Earth’s surface for millions of yearsEvidence supporting continental driftContinents look like they fit togetherSimilar rocks, minerals, and fossils are found on different continents in areas that look like they once fit together.
18Evidence for Crustal Movement Plate TectonicsEarth’s crust is divided into several sections (plates) that move across Earth’s surface.2
19Evidence for Crustal Movement 6 min videoPlates move due to convection cells produced by unequal heating of the fluids within the asthenosphere.
20Evidence for Crustal Movement There are three types of plate interactionsDivergent boundariesConvergent boundariesTransform boundaries
21Evidence for Crustal Movement Divergent BoundariesPlates move apart from each otherNew crust is formed hereMost commonly found at mid-ocean ridges and develop deep rift valleys.
22Evidence for Crustal Movement Convergent BoundariesPlates move toward each otherWhen 2 continental plates meet mountains are formed.Himalayan Mountains formed like this
23Evidence 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.
24Evidence for Crustal Movement Transform BoundariesPlates slide horizontally past one anotherTension builds as plates slide and when tension is released earthquakes occur.San Andreas Fault is an example
26Evidence for Crustal Movement The ocean floor appears to be spreading based on two major pieces of evidence.The age of igneous rocks increases as the distance from the mid-ocean ridges increases.Parallel strips of igneous rocks on either side of the mid ocean ridge show periodic reversals of magnetic polarity.