11

Earthquakes and The Earth’s Interior

GLY 2010 - Summer 2015 - Lecture 14

22

Earthquake

• A sudden motion or trembling in the Earth caused by the abrupt release of slowly accumulated strain

• Strain is a change in the shape or volume of a body as a result of stress

33

Seattle Earthquake, 2/28/01

• Movie of Microsoft laboratory during the earthquake

• Bill Gates was giving a presentation when the quake occurred

44

Focus, aka Hypocenter

• The initial rupture point of an earthquake, where strain energy is first converted to elastic wave energy

• The point within the Earth which is the center of an earthquake

55

Epicenter

• The point on the Earth's surface that is directly above the focus of an earthquake

66

Seismograph

• An instrument that detects, magnifies, and records vibrations of the Earth, especially earthquakes

• The resulting record is a seismogram

77

Principle of the Modern Seismograph

Seismograph Animation

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Example Seismogram

• Seismogram showing an earthquake - the three different traces represent vibrations in different directions

• First peaks are P waves, the second peaks the S waves

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Microearthquake Seismogram

• Magnitude 1.8 quake, Japan• N = North South

Orientation• E = East-West Orientation• Z = Vertical orientation• This earthquake had only P

and S waves – surface waves did not develop

1111

Moderate Earthquake Seismogram

• Magnitude 5.1 quake, Norwegian Sea

• Note well-developed surface waves (Love and Rayleigh) which have much greater amplitude than the P and S waves

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Richter Scale• Numerical scale of earthquake

magnitude• Devised in 1935 by the

seismologist C.F. Richter• Defined local magnitude as

the logarithm, to the base 10, of the amplitude in microns of the largest trace deflection that would be observed on a standard torsion seismograph at a distance of 100 km from the epicenter

1313

Richter Scale Continued

• Measures the vibrational amplitude of the earth in response to seismic waves

• Does NOT measure the energy release

1414

Mercalli Scale

• Arbitrary scale of earthquake intensity, ranging from I (detectable only instrumentally) to XII (causing almost total destruction)

• Based on human perception of the earthquake, and damage observed after the earthquake is over

1515

Number of Earthquakes/Year

1616

Isoseismal Map, Loma Prieta Earthquake,

1989

• A different view• This earthquake

stopped the World Series of 1989 for several days

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Isoseismal Map of Prince William Sound Earthquake, 1964

1818

Prince William Sound Earthquake Damage

19

Anchorage Building

• J.C. Penney building• Very little damage to adjacent building, with

steel-frame construction 19

2020

Energy Released by Earthquakes

• A great earthquake releases the equivalent of 1 billion tons of TNT or more, over a period of 1-2 minutes

• Most intense energy release per unit time of any natural event, except meteorite impact

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Catastrophic Event

Energy Releases

2222

Areal Distribution of Earthquakes

Current US Seismicity

23• Current as of 7/7/15 at 13:10 EDT

2424

Seismicity of the United States, 1990 - 2000

2525

Seismicity of Alaska, 1990 - 2000

• Many earthquakes are associated with the Aleutian Island Volcanic Arc, located above a subduction zone

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Seismicity of Hawaii, 1990 - 2000

• Most earthquakes on the the big island of Hawaii, associated with Hot Spot volcanism

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• Peak Acceleration as a percent of g, with 2% probability of exceedence in 50 years

Seismic Hazard – 2008 Map

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Western Hemisphere Seismic Risk

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Global Seismic Hazard

• Peak Acceleration as a percent of g, with 2% probability of exceedence in 50 years

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Depth of Focus

• Earthquakes are classified by the depths of their foci below the surface, as follows: Shallow 0-70 kilometers Intermediate 70-300 kilometers Deep 300-700+ kilometers

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Indonesia Earthquake

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Cause of Indonesian Earthquake

3333

Worldwide Recent Earthquakes

Tuesday, July 7, 2014 about  15:19 EDT

Worldwide Recent Earthquakes

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• Tuesday, July 7, 2015 about  13:20 EDT

3535

Afghanistan Seismicity

3636

Earthquake Damage

• Earthquakes can cause damage in a number of ways Building Collapse Tsunami waves Seiche waves Landslides Liquefaction Fire Disease

3737

Building Collapse

• Izmit, Turkey Earthquake, August 17, 1999

• Magnitude 7.4• Click video to play

(with sound)

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Collapse Studies

• Video from the Pacific Earthquake Research Center

• Shake Table Demonstration of Column Collapse

• From KRON, Channel 4, San Francisco, CA

3939

Tsunami

• Gravitational sea wave produced by any large-scale, short-duration disturbance of the ocean floor

• Disturbances caused principally by a shallow submarine earthquake, but also by submarine earth movement, subsidence, or volcanic eruption

Tsunami Animation

4141

Indonesian Tsunami

• Animation of tsunami movement across Indian Ocean

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Tsunami Velocity

42

4343

Phuket, Thailand Video

• Home video of tsunami hitting

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Tsunami Damage

Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley

4545

Tsunami Harbor Damage

• Photo: Joseph Penzien, Steinbrugge Collection

4646

Sri Lanka - Before

4747

Sri Lanka - After

Tohoku Earthquake, 3-11-11

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Seiche

• Free or standing-wave oscillation of the surface of water in an enclosed or semi-enclosed basin (as a lake, bay, or harbor)

5050

Landslides

• Earthquakes may trigger mass movement of rock and sediment on unstable slopes

• Damage is most likely to occur after fire removes vegetation, or clear-cutting of forests

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Quake Triggered Landslide Damage

5252

Landslide Damage, Continued

5353

House Destroyed by Landslide

5454

Public Policy

• Rebuilding allowed if no immediate threat of injury or death

• Liability waiver mandatory

5555

Liquefaction

• Liquefaction is a physical process that takes place during some earthquakes that may lead to ground failure

• As a consequence of liquefaction, soft, young, water-saturated, well sorted, fine grain sands and silts behave as viscous fluids rather than solids

Liquefaction Animation

5757

Liquefaction Failure

• Steinbrugge Collection

5858

Liquefaction Failure

• Steinbrugge Collection

5959

Fire• Fire often does more damage than the earthquake

itself Underground pipelines and tanks rupture Above ground tanks may rupture or tip over, spilling

contents Water lines break Streets are blocked by debris Downed electrical lines may spark, setting off fires

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Fire

• Photo: Arnold Genthe, Steinbrugge Collection

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San Francisco, 1906

After the fire

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Managua, Nicaragua

• Photo: Karl V. Steinbrugge

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Tilted Gasoline Tank

• Steinbrugge Collection

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Disease

• Earthquakes can cut underground sewer and water lines

• No drinking water• Only available water is contaminated

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Broken Sewer Pipe, Chile

• Photo: Karl V. Steinbrugge

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Seismic Wave Types

• There are several types of seismic waves• P(rimary) waves are the fastest• S(econdary or shear) waves are the next

fastest• L (surface) waves are the slowest

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P Wave Diagram

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S Wave Diagram

P and S Wave Animation

7070

Surface Waves

• Travel only along the surface, not through an object

• Generated by P and S waves interacting with the surface

• Slowest type of seismic waves• Cause the most damage to structures, and

generally cause the most deaths

7171

Rayleigh Waves

Rayleigh waves are one type of surface waves

7272

Rayleigh Waves

• First described by Lord Rayleigh in 1885• Rayleigh waves are created by rock particles moving

forward, up, backward, and down in elliptical orbits oriented in a vertical plane that includes the direction of propagation

• This produces a distinct rolling motion of the surface

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Love Waves

• Love waves are the other type of surface wave

7474

Love Wave Damage

• Love waves were named after A.E.H. Love, who first described them in 1912

• The rock moves from side to side in a horizontal plane at right angles to the direction of travel

Seismic Wave Animation

7676

Reflection and Refraction

Wave Reflection and Refraction

77

78

Haitian Earthquake

• On January 12, 2010 a magnitude 7.0 earthquake struck with epicenter near Léogâne, about 25 kilometers west of Port-au-Prince, Haiti

• An estimated three million people were affected by the quake

• Haitian Government reports estimated 230,000 people had died, 300,000 had been injured and 1,000,000 made homeless.

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Haiti Earthquake Location

• The location and focal mechanism suggest that the January 2010 quake was caused by a rupture of the Enriquillo-Plaintain Garden fault, which had been locked for 250 years, gathering stress

• The rupture was roughly 65 kilometers long with mean slip of 1.8 meters

• Preliminary analysis of the slip distribution found amplitudes of up to about 4 meters using ground motion records from all over the world

• Quake location was in the vicinity of the northern boundary where the Caribbean tectonic plate shifts eastwards by about 20 millimeters per year in relation to the North American plate.

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2010 Chile Earthquake• The 2010 Chilean earthquake occurred off the coast of the

Maule Region of Chile on February 27, 2010• The earthquake triggered a tsunami which devastated several

coastal towns in south-central Chile and damaged the port at Talcahuano

• Tsunami warnings were issued in 53 countries, causing minor damage in the San Diego area of California and in the To-hoku region of Japan, where damage to the fisheries business was estimated at US $66.7M

• Seismologists estimate that the earthquake was so powerful that it may have shortened the length of the day by 1.26 microseconds

• Precise GPS measurement indicated the telluric movement moved the entire city of Concepción 3.04 metres to the west.

• The latest death toll as of May 15, 2010 is 521 victims

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Chile Earthquake Location

• The earthquake took place along the boundary between the Nazca and South American tectonic plates, at a location where they converge at a rate of 80 millimeters a year.

• This earthquake was characterized by a thrust-faulting focal mechanism, caused by the subduction of the Nazca plate beneath the South American.

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Chile Earthquake Effects

• Chile has been at a convergent plate boundary that generates megathrust earthquakes since the Paleozoic (500 million years ago)

• The segment of the fault zone which ruptured in this earthquake was estimated to be over 700 km long with a displacement of almost 10 meters

• GPSstudies indicate that the earthquake shifted Santiago 28 cm to the west-southwest and moved Concepción at least at least 3 meters to the west