Download Orogenesis MAJOR OROGENS OF THE

Orogenesis
Lecture 15:
EARTHQUAKES
mountain building by tectonic forces due
to the movement of crustal plates
Æ Orogenic belts
mainly form
convergent plate
boundaries
Geog 1000 Introduction to Physical Geography Fall 2012 : Dr. Hester Jiskoot, University of Lethbridge
MAJOR OROGENS OF THE WORLD
TWO STRUCTURAL REGIONS
Cordilleran
Eurasian-Himalayan
Alps (Alpine orogeny)
20-120 my BP
THE CAUSES AND DISTRIBUTION OF EARTHQUAKES
• Earthquakes are caused by tectonic activity
• Tectonic activity (divergence/convergence/transverse motion) along plate
boundaries cause fault zones
• Most earthquakes located in narrow belts where oceanic plates subduct
under continental plates
Rocky Mountains (Laramide orogeny)
40-80 my BP
Himalayas (Himalayan orogeny)
45-54 my BP
Earthquakes occur along major fault zones in the crust
Tectonic earthquake terms
epicentre
focus
slip measurements
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Seismic waves
Earthquakes in subduction zone
Earthquake motion occurs at different depths along subduction zones
Think: coiled spring
Think: rope
Volcanism
P waves (Compressional
or primary waves)
• travel at speeds of 1.5 to 8 km/s in the Earth's crust
• shake the ground in the direction they are propagating
S waves (Shear or secondary waves)
• shake perpendicularly or transverse to the direction of propagation
• travel at 60% to 70% of the speed of P waves.
Crust destroyed
8 Oct 2005 Pakistan Earthquake
Predicted P-wave travel times in minutes
FIRST MEASUREMENT INSTRUMENT
Seismoscope
Between the heavy black lines is the P-wave shadow zone
• Invented in China 132 AD
• Wine jar with 2 m diameter
• Balls held in dragons’ mouths:
8 dragons, 1 in each of the
compass directions
• Shaking released balls into
toads’ mouths
• First ball released indicated
direction towards earthquake
epicenter
Chang Heng's seismoscope
http://earthquake.usgs.gov/
MEASUREMENT INSTRUMENTS
MEASUREMENT SCALES
Seismograph
1902 Mercalli: intensity Æ I to XII
Damage indicator
1935
Need ≥ 3 for epicentre location
Seismometer
Richter: amplitude-magnitude Æ 1.0 to >8.0 logarithmic
Measure of seismograph amplitude
1993 Moment-magnitude Æ 1.0 to >8.0 logarithmic
Measure of fault's length, depth and its slip
Modern Digital Seismometer Æ
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Richter
magnitude
scale
diagram
RICHTER
MAGNITUDE
EARTHQUAKE EFFECTS
< 3.5
Generally not felt, but recorded.
3.5-5.4
Often felt, but rarely causes damage.
< 6.0
At most slight damage to well-designed buildings,
but major damage to poorly constructed buildings
over small regions.
6.1-6.9
Can be destructive in areas < 100 km
7.0-7.9
Major earthquake. Can cause serious damage over
larger areas.
> 8.0
Great earthquake. Can cause serious damage in
areas >100 km across.
HOW OFTEN DO EARTHQUAKES OCCUR ?
Earthquakes > M 8 are called ‘great earthquakes’
and occur about once every 15 years
Average number of earthquakes per year along major faultzones at shallow depth (0-70 km) and with magnitude ≥ 5
Ten largest
earthquakes
since 1900
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http://neic.usgs.gov/neis/density/eq_density.html
1
2
3
4
5
6
7
8
9
10
4
Chile
Prince William Sound, Alaska
Andreanof Islands, Aleutian Islands
Kamchatka
Off the Coast of Ecuador
Rat Islands, Aleutian Islands
India-China Border
Kamchatka
Banda Sea, Indonesia
Kuril Islands
Northeast Indian Ocean (off Sumatra)
1960
1964
1957
1952
1906
1965
1950
1923
1938
1963
2004
Magnitude
(Richter)
9.5
9.2
9.1
9.0
8.8
8.7
8.6
8.5
8.5
8.5
9.0
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EFFECTS OF EARTHQUAKES
Damage on Fault trace
Dependent on the following factors:
1) Intrinsic to the earthquake
- its magnitude, type, location (epicenter) and depth (focus)
2) Local geological conditions
- distance from the event, path of the seismic waves
- bedrock type and degree of water saturation
3) Societal conditions reacting to the earthquake
- quality of construction, preparedness, time of day
Rising sewage tank
due to
liquefaction
Comparison of two earthquakes in 1989
Earthquake
induced
landslides
and
rockslides
Damage after the 1989 earthquake in Armenia
Magnitude 7.1 Loma Prieta earthquake in leastpopulated area of the San Francisco peninsula.
- population well prepared and well-engineered buildings
- rush hour, but few cars on the roads: large opening game on TV
- ~ 67 deaths.
Magnitude 6.7 earthquake in war-torn Armenia
(between Russia & Turkey)
- epicenter much closer to major cities
- poorly-engineered houses of un-reinforced concrete collapsed
- night-time: everyone in the house in bed: unprepare
- > 25 000 deaths.
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12 Jan 2010: Haiti 7.0 magnitude earthquake
222,570 people killed
300,000 injured
1.3 million displaced
Tsunami
™ A large wave of a series of water waves caused by the displacement of a large
volume of a body of water in oceans/seas/large lakes.
™ Generated by disturbances above or below the water.
¾ At plate boundary between the Caribbean and North America plate.
™ Disturbances include earthquakes, volcanic eruptions, underwater (nuclear)
explosions, landslides, meteorite ocean impacts, etc.
™ Large tsunamis most often caused by earthquakes.
EARTHQUAKE THAT
CAUSED THE
26 DEC 2005 TSUNAMI
IMPACT OF DEC 26th TSUNAMI ON BANDA ACEH, SUMATRA
10 Jan 2003
29 Dec 2005
India plate moves NE at a rate
of 6 cm/yr relative to the
Burma plate.
This megathrust earthquake
made ~1200 km of plate
boundary slip
REDRAW WORLD COASTAL MAPS
Average fault plane
displacement was 15 m
Sea floor overlying thrust fault
uplifted by several meters
IKONOS satellite images
http://www.nature.com/news/2005/050103/full/050103-2.html
Seismograph of 3 Jan 2008 earthquake 43 km S of Lethbridge
Depth ~25 km
Magnitude 3.5 ML
Earthquakes <100km radius
since 1985
Lethbridge
5
Earthquakes in the last day, weeks, years
Red = 24 hours before 15 Oct 2012 15:00 local time
WHY
EARTQUAKES
NEAR
LETHBRIDGE?
http://www.lithoprobe.ca/
http://www.iris.edu/seismon/
Reading for Monday
Chapter 9 p. 323-331
Volcanism
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