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1 Chapter 6 Key Terms Tension Strain Fault Seismometer Epicenter Tsunami Shear Joint Richter Scale Divergent Boundary Convergent Boundary Transform Boundary 2 Chapter 6 EARTHQUAKES 3 Earthquake Series of low-frequency shock waves traveling through the earth What causes these earthquakes? The tectonic plates 4 Plate Tectonics Theory Earth’s crust is made up of many plates Plates are in constant motion Plate edges (margins) can collide Earthquake waves are emitted from this collision 5 Forces Stress Force exerted inside a material Compression Tension Shear Most important in producing earthquakes 6 Boundaries Divergent Boundaries Margin Convergent Boundaries Margin where plates are moving away from each other where plates are moving toward each other Transform Boundaries Margin where plates slide past each other 7 Strain Any change in shape of a solid under stress The amount of strain a material can endure without breaking is related to its ductility Elasticity also helps determine the magnitude of the earthquake 8 Earthquake Article Find an article about a major earthquake that has happened in the past 50 years Read the article and write a summary about the article The summary must be at least 200 words Include source at end of summary DO NOT USE WIKIPEDIA!!! Due December 2nd 9 Faults & Joints Joint Stress crack in a rock Fault When sections of rock on both sides of the joint move along the fracture Formed Occur by tectonic activity between all tectonic plates 10 Describing Faults Strike The direction of a fault Dip Angle of the fault face downward from the horizontal 11 Classifying Faults Dip-slip Fault Fault whose motion is parallel to its dip (up and down) 2 types of dip-slip faults Normal Fault When Reverse Fault When the block above the fault dropped the block above rises Strike-slip Fault Horizontal motion in the fault 12 Faults and Earthquakes Most earthquakes that we can feel happen at depths less than 45 miles below the surface If the rocks move easily across each other, no earthquake occurs A “locked” fault builds up stress When the stress becomes too much, the rocks suddenly fracture, causing a release in a large amount of energy Aftershocks – secondary earthquakes 13 Seismology Seismometers – detect earthquake waves Measure both amplitude and frequency of waves 14 15 Seismology Seismometers – detect earthquake waves Measure both amplitude and frequency of waves Seismograph – has both seismometer and a way to record the changing waves Seismogram – the recording from a seismograph 16 17 18 Types of Seismic Waves Body waves – waves that pass right through the earth P Waves (Primus) Fastest body waves; first to arrive Longitudinal compression waves 19 Types of Seismic Waves Body waves – waves that pass right through the earth S Waves (Secundus) Slower but stronger waves Transverse Cannot or shear waves pass through liquid or gas 20 Types of Seismic Waves Surface Waves – travel along earth’s surface Move at relatively the same speed as S waves, but are more destructive because they affect buildings on the surface 21 22 Types of Seismic Waves Surface Waves – travel along earth’s surface Move at same speed as S waves, but are more destructive because they affect buildings on the surface 2 forms of surface waves Rayleigh Love – move in a vertical, circular motion – move horizontally 23 24 25 Locating Earthquakes Focus Exact location of plate movement underground Epicenter Directly above focus on the surface 26 Locating Earthquakes Seismologists can know exactly where an earthquake originated based on the arrival of P and S waves Triangulation Using 3 stations to pinpoint the location of the epicenter 27 28 Locating Earthquakes Seismologists can know exactly where an earthquake originated from based on the arrival of P and S waves Triangulation Using 3 stations to pinpoint the location of the epicenter Most earthquakes happen along tectonic plate boundaries Pacific Rim – aka “Ring of Fire” Others can happen along fault lines 29 30 Effects of Earthquakes Richter Scale Units Not of magnitude – energy released by the earth’s movement a linear relationship – exponential relationship 31 32 Effects of Earthquakes Richter Scale Units Not a linear relationship – exponential relationship Each No of magnitude – energy released by the earth’s movement unit on the Richter scale is 31.6 times more energy upper limit (maximum value) Not very accurate above magnitude 7 or from distances greater than 700 km Moment Magnitude Scale 33 34 Effects of Earthquakes Intensity Measure of how much damage actually results Depends on many things Richter Depth scale magnitude of focus Damage done to buildings Duration Modified From XII Mercalli Intensity Scale (MMI) I – XII is most destructive 35 Earthquake Hazards Building collapse Fire Tsunamis Landslides 36 Earthquake prediction Even with all the technology, we cannot predict earthquakes Scientists study earthquakes and where they happen to chart earthquake prone regions Even with much information, we still cannot predict the day or hour an earthquake will happen
