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.
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
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
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
Tsunamis (Not Tidal Waves!) Safest & Most Dangerous Buildings: Safest & Most Dangerous Buildings Small, Wood-frame House - Safest
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
Tide & Weather Magnitude and Intensity : Magnitude and Intensity Intensity
How Strong Earthquake Feels to Observer
Related to Energy Release
Determined from Seismic Records
Rough correlation between the two for shallow earthquakes Intensity: Intensity How Strong Earthquake Feels to Observer
Distance to Quake
Type of Building
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
No Upper or Lower Bounds
Largest Quakes about Mag. 8.7
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
Dilatancy - Diffusion
Stick - Slip
Seismic Gaps : Seismic Gaps