Earthquakes

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?

Earthquakes-causes and effects Prof. D Chandrasekharam Department of Earth Sciences Head, Centre of Studies in Resources Engineering Indian Institute of Technology Bombay

Earth structure and Interior

Continental drift

Earth structure and Interior

Plate boundaries

Pacific ridge

Indian Ocean Ridge Atlantic ridge

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Plate boundaries

Plate boundaries Constructive boundary

Destructive boundaries

Himalayas Sumatra

Japan

Continental crust

California

Ocean crust

Types of collision tectonics

Pakistan Earthquake 7.2M

Subduction Continent-Continent

Earthquake foci

Earthquakes in 2005

Ring of Fire

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Indian Ocean Floor

Types of faults

Mumbai 10 Ma

Fracture 38 Ma 55 Ma

75 Ma

Earthquake terms

Locating an earthquake Seismograph

USA

Japan

Bombay Arrival of “P” wave

Tectonic map of India

Arrival of “S” wave

Seismic Profile

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Earthquake Magnitude

TNT Equivalent Richter TNT for Seismic Magnitude Energy Yield

Earthquake 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.

Sumatra

-1.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0

6 ounces 30 pounds 320 pounds 1 ton 4.6 tons 29 tons 73 tons 1,000 tons 5,100 tons 32,000 tons 80,000 tons 1 million tons 5 million tons 32 million tons

7.5 8.0 8.5 9.0 10.0 12.0

160 million tons 1 billion tons 5 billion tons 32 billion tons 1 trillion tons 160 trillion tons

Example (approximate) Breaking a rock on a lab table Large Blast at a Construction Site Large Quarry or Mine Blast

Small Nuclear Weapon Average Tornado (total energy) Little Skull Mtn., NV Quake, 1992 Double Spring Flat, NV Quake, 1994 Northridge, CA Quake, 1994 Hyogo-Ken Nanbu, Japan Quake, 1995; Largest Thermonuclear Weapon Landers, CA Quake, 1992 San Francisco, CA Quake, 1906 Anchorage, AK Quake, 1964 Chilean Quake, 1960 (San-Andreas type fault circling Earth) (Fault Earth in half through center, OR Earth's daily receipt of solar energy)

Volcanoes and earthquake foci-Indonesia

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Can we predict an earthquake? Science has not reached that stage as yet!!

Thank You

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