Strain

Elastic Rebound

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(point on surface directlyabove the focus)

(point of rupture)

P Waves

Fastest waves, first to arrive

S Waves

Slower waves, second to arrive

Surface Waves

Slowest waves, last to arriveOrbital motionDo the most damage

Seismometer

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Seismogram

Travel-time graph

Fit the time differencebetween the first P-waveand first S-wave in-betweenthe blue curves

Read off distance toepicenter

Great circles

Travel-time graph tellsyou how far away youare from the epicenter,but not the direction.

Need three seisomgraphstations to triangulatethe location of theepicenter.

Magnitude

Intensity

Evaluation of the severity of an earthquake at a given location.

Variables:

1. Distance from the earthquake

2. Total amount of energy released by the earthquake

3. Material type

Liquefaction

Water-rich clays liquefy during shaking

Mercalli Intensity ScaleXII - Damage nearly total. Large rock masses displaced. XI - Rails bent greatly. Underground pipelines completely out of service. X - Most masonry and frame structures destroyed. Some well-built wooden structures and bridges destroyed. Serious damage to dams, dikes, embankments. Large landslides. Rails bent slightly. IX - General Panic. Poor masonry destroyed, ordinary masonry heavily damaged, sometimes with complete collapse, reinforced masonry damaged, general damage to foundations. Frame structures, if not bolted, shifted off foundations. Frames racked. Underground pipes broken. Conspicuous cracks in ground. Liquefaction in areas of sand and mud. VIII - Steering of cars affected. Damage to ordinary masonry, partial collapse. Twisting, fall of chimneys, factory stacks, monuments, towers, elevated tanks. Frame houses moved on foundations if not bolted down; loose panel walls thrown out. Cracks in wet ground and on steep slopes. VII - Difficult to stand. Noticed by car drivers. Furniture broken. Damage to weak masonry, some cracks in ordinary masonry. Weak chimneys broken at roof line. Fall of plaster, loose bricks, stones, tiles and unbraced parapets. VI - Felt by all. Persons walk unsteadily. Windows dishes and glasses broken. Pictures off walls. Furniture moved or overturned. Weak plaster and masonry cracked. V - Felt outdoors, sleepers wakened. Liquids disturbed or spilled. Small unstable objects displaced or upset. Pictures move. IV - Hanging objects swing. Windows, doors, dishes rattle. Vibration like passing of heavy truck or jolt like a heavy ball striking the walls. III - Felt indoors. Hanging objects swing. Vibration like passing of light trucks. II - Felt by persons at rest, on upper floors, or favorably placed. I - Not felt.

Measures the intensity of a ‘quake relative to agiven location away from the epicenter.

Earthquake severity

Intensity Map

1971 San Fernando Earthquake

MagnitudeTotal amount of energy released by the earthquake

Richter Scale

Richter ScaleRichter Magnitude How many kilograms of TNT would have this much energy?

0 0.61.0 20 2.0 600 * Smallest quake people can normally feel3.0 20 000 * Most people near epicenter feel the quake

* Nearly 100,000 occur every year of size 2.5 - 3.04.0 60 000 * A small fission atomic bomb

* Quakes above 4.5 can cause local damage5.0 20 000 00 * A standard fission bomb, similar to the first bomb tested in New Mexico, U.S.6.0 60 000 000 * A hydrogen bomb; can cause great damage locally

* About 100 shallow quakes of size 6.0 every year7.0 20 billion * Major earthquake; about 14 every year

* Enough energy to heat New York City for 1 year * Large enough to be detected all over globe

8.0 60 billion * Largest known: 8.9 in Japan and in Chile/Ecuador * San Francisco destroyed by 8.25 in 1906

9.0 20 trillion * Roughly the world’s energy usage in a year

Each unit is 32-fold energy increase

Earthquake Distribution Map

Earthquake Hazards Map

Some Famous Earthquakes

1811 New Madrid, Missouri: 7.8-91886 Charleston, South Carolina: 6.71906 San Francisco, California: 8.31964 Anchorage, Alaska: 8.61983 Saranac Lake, New York 5.11989 Loma Prieta, California: 7.01994 Northridge, California: 6.41995 Kobe, Japan: 6.8

New Madrid

San Andreas Fault

San Andreas Fault

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1964 Alaskan Quake

Anchorage

Tsunami

Unimak Island, Alaska. Wave moving at 800km/hr, 18m high

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P wave shadow zone

P waves slow down and are refracted in liquids

S wave shadow zone

S waves do not travel through molten metallic liquids