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Eric Marti/AP Photo

Earthquakes (ch 13)

1. Why do we care?2. What is an e-quake?3. How are they recorded and studied?4. Where do they occur5. Magnitude and intensity 6. prediction

Why we care?1. Destruction, injury, death

1906 SanFransisco -- FIREEarthquakes don’t kill people, buildings do

A. ShakingB. FireC. Falling into cracks/fissuresD. Building collapse

Seven largest earthquakesDate Location Name Magnitude

May 22, 1960 Valdivia, Chile1960 Valdivia earthquake

9.5

March 27, 1964Prince William Sound, Alaska, USA

1964 Alaska earthquake

9.2

December 26, 2004Indian Ocean, Sumatra, Indonesia

2004 Indian Ocean earthquake

9.1–9.3

March 11, 2011Pacific Ocean, Tōhoku region, Japan

2011 Tōhoku earthquake

9.0[3][4][5]

November 4, 1952Kamchatka, Russia (then USSR)

1952 Kamchatka earthquakes

9.0[2]

November 25, 1833 Sumatra, Indonesia1833 Sumatra earthquake

8.8–9.2 (est.)

February 27, 2010 Maule, Chile2010 Chile earthquake

8.8

Seven most deadly earthquakesDeadliest earthquakes[12]

Rank Name Date Location Fatalities Magnitude

1 "Shaanxi"January 23, 1556

Shaanxi, China820,000–830,000 (est.)[13] 8.0 (est.)

2 "Tangshan"July 28, 1976

Tangshan, China 242,419–655,000 7.5–7.8

3 "Haiti"January 12, 2010

Haiti

316,000(Haitian sources)50,000–92,000 (non-Haitian sources)

7.0

4 "Antioch" May 21, 526Antioch, Turkey (thenByzantine Empire)

250,000[15] 7.0 (est.)[16]

5 "Gansu"December 16, 1920

Ningxia–Gansu, China 235,502[17] 7.8

6"Indian Ocean"

December 26, 2004

Indian Ocean, Sumatra, Indonesia

230,210+[18][19] 9.1–9.3

7 "Aleppo"October 11, 1138

Aleppo, Syria 230,000 Unknown

Just because an earthquake is powerful……...doesn’t mean it is deadly

1. Where and when could earthquakes occur?2. How big and damaging are they?3. What do earthquakes tell us about the earth?

Left: Photo taken prior to the earthquake. Low income housing- unreinforced masonry.

Below: After

BBC

Magnitude 7.0 HAITITuesday, January 12, 2010 at 21:53:09 UTC

Haiti 2010: Small earthquake, very deadly

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BBC

Magnitude 7.0 HAITITuesday, January 12, 2010 at 21:53:09 UTC

Bike trip along west coast of MexicoWhat hazard did I subject myself to?

December 26, 2004 Indian Ocean tsunami(Sumatra, 2004 earthquake)

Destruction from Dec 26, 2004 Indian Ocean tsunami

Number of deaths = 250,000

Other tsunamisMay, 1782 Taiwan 50,000August, 1883 Indonesia 36,000October, 1707 Japan 30,000June 1896 Japan 27,000

Great Wave off the Coast of Kanagawa, by Hokusai, a famous late eighteenth- and early nineteenth-century Japanese artist.

Tsunami: a Japanese word for "harbor wave.""tsu“ = harbor"nami," = wave

Minimize the danger from tsunamis….

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What is a Tsunami?series of waves generated in water by a disturbance that vertically displaces the water column.

What processes generate tsunamis?A) EarthquakesB) landslides C) volcanic eruptionsD) impact of cosmic bodies E) All of the above

Why we care?2. Key earth process

Mountain building Earth structure

Seismology: study of earthquakes

1. Where and when could earthquakes occur?2. How big and damaging are they?3. What do earthquakes tell us about the earth?

2. What is an earthquake?

Earthquake:

Earthquake: vibration of Earth produced by rapid release of energy

Waves (energy) radiate in all directions from focusfocus is a point on a fault plane

Epicenter is point on the surface above focus

FOCUS

Earthquake depths: typically 0-100 km

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Why are most earthquakes within 100 km of Earth’s surface

Environment Temperature Pressure Behavior

surface low low

Greater depths

high high

This earthquake occurred on the subduction zone plate boundary where the oceanic Nazca Plate subducts beneath the South American Plate.

The two plates are converging at a rate of about 8 cm/yr.

Earthquakes are products of plate motion:

Nazca Plate

South American Plate

UNAVCO

Regional TectonicsThis map shows the rates and directions of motion of the Cocos, Pacific, and Caribbean plates with respect to the North American Plate. The Caribbean Plate moves eastward at a rate of 2 cm/year.

Pacific

PlateCocos Plate

North American Plate

Caribbean Plate

Transform Plate Boundaries (yellow lines)

Divergent Plate Boundaries (red lines)

Earthquakes are products of plate motion:

Earthquakes are products of plate motion:WHY is there an instantaneous release of energy?

1. In many places, plates do not slowly grind past each other

2. Instead: there is no motion across a fault for some interval

strain accumulates, and is then released during an earthquake

Elastic rebound during earthquake

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2 types of faults

2. Strike-slip: movement primarily along strike of the fault surface

1. Dip-slip: movement primarily along DIP of the fault surface

Vertical displacement horizontal displacement

Map of deformation: Dec 2004 Sumatra earthquak

From: NASA Natural Hazards web page

3. Measuring EarthquakesSeismometers and Seismographs

Ancient Chinese Seismometer

3. Measuring Earthquakes(Seismometers/Seismographs)

Kinematics

Digital Seismograph

Namche STS2

Seismometer

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apkota,Tumlingtr

Sumatra Earthquake: Dec 20042nd largest in recorded history

How does an earthquake cause a tsunami? water column must be

Foreshock, mainshock, aftershock sequence

Aftershocks: series of smaller earthquakes typically follow a major earthquake

hours to days after main shock

Aftershocks

This earthquake was followed by five powerful aftershocks within the first two hours after the devastating quake.

USGS

In the first eleven hours after the earthquake there have been 32 aftershocks greater than magnitude 4.

Google Earth

Magnitude 7.0 HAITITuesday, January 12, 2010 at 21:53:09 UTC

Aftershock map: Turkey, 1999 10 days following main quake

Red M >= 5; yellow M >= 4; Green >= 2.5

IV. Earthquakes and energy: 3 types of wavesp-waves, s-waves, surface waves

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P-waves1. first to arrive2. material compresses then expands volume of material is changed3. travel 1.7 times faster than “s-waves”

S-waves1. second to arrive2. material vibrates from “side to side” shape is changed3. do not travel through fluids

Surface waves1. last to arrive2. source of most damage

What happens to a wave of seismic energy as it moves away from focus?

Energy decreases with distance:1. it is spread out over a greater area (or volume)2. loss to friction

4. Locating earthquakes

Locate earthquakes to assess hazard and study earth processes

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Step 1. Seismic Travel-time Curve -determine distance to source

KEY: The separation (in time) of P and S-waves increases with distance

Step 2: once you know distance, triangulate to find the Epicenter

Station B5600 km

Station C8600 km

Station A1500 km

Epicenter located using three seismographs

Locating earthquakes.

Where do earthquakes occur?

http://www.iris.edu/servlet/eventserver/map.do

13 major platesmany have oceanic and continental crust

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Japan Seismicity 1990 - present

Deep

Shallow

Seismicity cross section

Volcanism, earthquakes and plate boundaries revisited.

1. nearly all earthquakes near plate boundaries2. most volcanoes near boundaries, with some exceptions

If earthquakes occur along plate boundaries…….Then what is going on in Missouri?

2 different ways to look at earthquake size

size of quake: Magnitude

size of effects: Intensities, Accelerations

related to energy

5. Earthquake Size

Maximum Amplitude of Ground Shaking Determines

Richter Magnitude

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Richter (local) Magnitude:

ML = log(A) + 3.0 A= amplitude (mm), “Wood-Anderson” sensor

100 km from source

Distance Correction

log(A)

Distance100 km

3.02.0

4.0

ML

Richter Magnitude Versus Energy

magnitude-frequency plot.

Earthquake size 2. Intensity of effects

“Mercalli Intensity Scale”

The earthquake occurred about 10 miles west of the capital of Haiti, Port-au-Prince, and caused extreme shaking.

Modified Mercalli IntensityPerceived

Shaking

Extreme

Violent

Severe

Very Strong

Strong

Moderate

Light

Weak

Not Felt

USGS Shaking Intensity

Magnitude 7.0 HAITITuesday, January 12, 2010 at 21:53:09 UTC

1999 Hector Mine earthquake Intensity Map

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1811 New MadridEarthquake IntensityMap

Loma PrietaIntensity Map

Geologic material at a site controls intensity of shaking

6. Predicting earthquakes

1. short-range forecasts: predict when an earthquake will occur on some fault

2. Long-range forecasts: predict likelihood (or probability) earthquake will occur in some area

Gaps in seismic activity most likely locations for earthquakes

Start with map of shaking, Add effects of soils and population density