Faults and Earthquakes

Information about Faults and Earthquakes

Published on October 29, 2007

Author: Marian

Source: authorstream.com

Content

Faults and Earthquakes :  Faults and Earthquakes Some Important Earthquakes :  Some Important Earthquakes 1755 - Lisbon, Portugal Killed 70,000, Raised Waves in Lakes all over Europe First Scientifically Studied Earthquake 1811-1812 - New Madrid, Missouri Felt over 2/3 of the U.S. Few Casualties 1886 - Charleston, South Carolina Felt All over East Coast, Killed Several Hundred. First Widely-known U.S. Earthquake Some Important Earthquakes :  Some Important Earthquakes 1906 - San Francisco Killed 500 (later studies, possibly 2,500) First Revealed Importance of Faults 1923 – Tokyo - Killed 140,000 in firestorm 1964 - Alaska Killed about 200 Wrecked Anchorage. Tsunamis on West Coast. 1976 - Tangshan, China Hit an Urban Area of Ten Million People Killed 650,000 How Seismographs Work:  How Seismographs Work Seismic Waves:  Seismic Waves Locating Earthquakes:  Locating Earthquakes Locating Earthquakes:  Locating Earthquakes Locating Earthquakes:  Locating Earthquakes Locating Earthquakes - Depth:  Locating Earthquakes - Depth Elastic Rebound:  Elastic Rebound Types of Faults:  Types of Faults Faults Are Classified According to the Kind of Motion That Occurs on Them Joints - No Movement Strike-Slip - Horizontal Motion Dip-Slip - Vertical Motion Epicenter and Focus:  Epicenter and Focus Focus Location within the earth where fault rupture actually occurs Epicenter Location on the surface above the focus Strike-Slip Fault – Left Lateral:  Strike-Slip Fault – Left Lateral Strike-Slip Fault – Right Lateral:  Strike-Slip Fault – Right Lateral Dip-Slip Fault - Normal:  Dip-Slip Fault - Normal Dip-Slip Fault - Reverse:  Dip-Slip Fault - Reverse Dip-Slip Faults:  Dip-Slip Faults Normal Faults: Extension Reverse Faults: Compression Reverse Faults are often called Thrust Faults Normal Fault Structures :  Normal Fault Structures Reverse Fault Structures :  Reverse Fault Structures Major Hazards of Earthquakes:  Major Hazards of Earthquakes Building Collapse Landslides Fire Tsunamis (Not Tidal Waves!) Safest & Most Dangerous Buildings:  Safest & Most Dangerous Buildings Small, Wood-frame House - Safest Steel-Frame Reinforced Concrete Unreinforced Masonry Adobe - Most Dangerous Tsunamis:  Tsunamis Probably Caused by Submarine Landslides Travel about 400 M.p.h. Pass Unnoticed at Sea, Cause Damage on Shore Warning Network Around Pacific Can Forecast Arrival Whether or Not Damage Occurs Depends on: Direction of Travel Harbor Shape Bottom Tide & Weather Magnitude and Intensity :  Magnitude and Intensity Intensity How Strong Earthquake Feels to Observer Magnitude Related to Energy Release Determined from Seismic Records Rough correlation between the two for shallow earthquakes Intensity:  Intensity How Strong Earthquake Feels to Observer Depends On: Distance to Quake Geology Type of Building Observer! Varies from Place to Place Mercalli Scale- 1 to 12 Isoseismals from the 1906 San Francisco Earthquake :  Isoseismals from the 1906 San Francisco Earthquake Intensity and Geology in San Francisco, 1906:  Intensity and Geology in San Francisco, 1906 Intensity and Bedrock Depth in San Francisco, 1906:  Intensity and Bedrock Depth in San Francisco, 1906 San Francisco and New Madrid Compared :  San Francisco and New Madrid Compared Magnitude - Determined from Seismic Records:  Magnitude - Determined from Seismic Records Richter Scale: Related to Energy Release Exponential No Upper or Lower Bounds Largest Quakes about Mag. 8.7 Magnitude-Energy Relation 4 - 1 5 - 30 6 - 900: 1 Megaton = about 7 7 - 27,000 8 - 810,000 Magnitude and Energy:  Magnitude and Energy Magnitude and Energy:  Magnitude and Energy Seismic - Moment Magnitude:  Seismic - Moment Magnitude A Seismograph Measures Ground Motion at One Instant But -- A Really Great Earthquake Lasts Minutes Releases Energy over Hundreds of Kilometers Need to Sum Energy of Entire Record Modifies Richter Scale, doesn't replace it Adds about 1 Mag. To 8+ Quakes Seismology and Earth's Interior:  Seismology and Earth's Interior Successive Approximation in Action 1. Assume the Earth is uniform.:  1. Assume the Earth is uniform. We know it isn't, but it's a useful place to start. It's a simple matter to predict when a seismic signal will travel any given distance. 2. Actual seismic signals don't match the predictions :  2. Actual seismic signals don't match the predictions If we match the arrival times of nearby signals, distant signals arrive too soon If we match the arrival times of distant signals, nearby signals arrive too late. Signals are interrupted beyond about 109 degrees 3. We conclude: :  3. We conclude: Distant signals travel through deeper parts of the Earth, therefore .. Seismic waves travel faster through deeper parts of the Earth, and .. They travel curving paths (refract) Also, there is an obstacle in the center (the core). Why Refraction Occurs:  Why Refraction Occurs Waves Travel The Fastest Path:  Waves Travel The Fastest Path Seismic Waves in the Earth:  Seismic Waves in the Earth Inner Structure of the Earth :  Inner Structure of the Earth The overall structure of the Earth:  The overall structure of the Earth Strategies of Earthquake Prediction:  Strategies of Earthquake Prediction Lengthen Historical Data Base Historical Records Paleoseismology Short-term Prediction Precursors Long-term Prediction Seismic Gaps Risk Levels Modeling Dilatancy - Diffusion Stick - Slip Asperities Crack Propagation Seismic Gaps :  Seismic Gaps

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