earthquakes-causes and effects · 2005-12-12 · earthquake magnitude earthquake severity richter...
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Earthquakes-causes and effects
Prof. D ChandrasekharamDepartment of Earth Sciences
Head, Centre of Studies in Resources EngineeringIndian Institute of Technology Bombay
Such news items raises several questions like�What are earthquakes?�How do they occur?�What are the causes and effects?�Can we prevent them?�Can we predict them?
Earth structure and Interior Earth structure and Interior
Continental drift
Plate boundaries
Atlantic ridge
Indian Ocean Ridge
Pacific ridge
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Plate boundaries
Continental crust Ocean crust
Constructive boundary Destructive boundaries
Plate boundaries
SumatraHimalayas
Japan California
Subduction Continent-Continent
Pakistan Earthquake 7.2MTypes of collision tectonics
Ring ofFire
Earthquake foci Earthquakes in 2005
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Indian Ocean Floor
38 Ma
10 Ma
55 Ma
75 Ma
Mumbai
Types of faults
Fracture
Earthquake terms Locating an earthquake
Seismograph
Japan
USA
Bombay
Arrival of “P” wave Arrival of “S” wave
Tectonic map of India Seismic Profile
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Earthquake MagnitudeEarthquake Severity Richter Magnitude Earthquake Effects Less than 3.5 Generally not felt, but recorded. 3.5-5.4 Often felt, but rarely causes damage. 5.4 - 6.1 At most slight damage to well-designed buildings.
Can cause major damage to poorly constructed buildings over small regions.
6.1-6.9 Can be destructive in areas up to about 100 kilometers across where people live. 7.0-7.9 Major earthquake. Can cause serious damage over larger areas. 8 or greater Great earthquake. Can cause serious damage in areas several hundred kilometers across.
TNT EquivalentRichter TNT for Seismic Example Magnitude Energy Yield (approximate) -1.5 6 ounces Breaking a rock on a lab table 1.0 30 pounds Large Blast at a Construction Site 1.5 320 pounds 2.0 1 ton Large Quarry or Mine Blast 2.5 4.6 tons 3.0 29 tons 3.5 73 tons 4.0 1,000 tons Small Nuclear Weapon 4.5 5,100 tons Average Tornado (total energy) 5.0 32,000 tons 5.5 80,000 tons Little Skull Mtn., NV Quake, 1992 6.0 1 million tons Double Spring Flat, NV Quake, 1994 6.5 5 million tons Northridge, CA Quake, 1994 7.0 32 million tons Hyogo-Ken Nanbu, Japan Quake, 1995; Largest Thermonuclear Weapon 7.5 160 million tons Landers, CA Quake, 1992 8.0 1 billion tons San Francisco, CA Quake, 1906 8.5 5 billion tons Anchorage, AK Quake, 1964 9.0 32 billion tons Chilean Quake, 1960 10.0 1 trillion tons (San-Andreas type fault circling Earth) 12.0 160 trillion tons (Fault Earth in half through center, OR Earth's daily receipt of solar energy)
Sumatra Volcanoes and earthquake foci-Indonesia
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Can we predict an earthquake?
Science has not reached that stage as yet!!
Thank You