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transcript
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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