earthquakes-causes and effects · 2005-12-12 · earthquake magnitude earthquake severity richter...

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1 Earthquakes-causes and effects Prof. D Chandrasekharam Department of Earth Sciences Head, Centre of Studies in Resources Engineering Indian 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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Page 1: Earthquakes-causes and effects · 2005-12-12 · Earthquake Magnitude Earthquake Severity Richter Magnitude Earthquake Effects Less than 3.5 Generally not felt, but recorded. 3.5-5.4

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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

Page 2: Earthquakes-causes and effects · 2005-12-12 · Earthquake Magnitude Earthquake Severity Richter Magnitude Earthquake Effects Less than 3.5 Generally not felt, but recorded. 3.5-5.4

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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

Page 3: Earthquakes-causes and effects · 2005-12-12 · Earthquake Magnitude Earthquake Severity Richter Magnitude Earthquake Effects Less than 3.5 Generally not felt, but recorded. 3.5-5.4

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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

Page 4: Earthquakes-causes and effects · 2005-12-12 · Earthquake Magnitude Earthquake Severity Richter Magnitude Earthquake Effects Less than 3.5 Generally not felt, but recorded. 3.5-5.4

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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

Page 5: Earthquakes-causes and effects · 2005-12-12 · Earthquake Magnitude Earthquake Severity Richter Magnitude Earthquake Effects Less than 3.5 Generally not felt, but recorded. 3.5-5.4

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Can we predict an earthquake?

Science has not reached that stage as yet!!

Thank You