Download Regents Earth Science – Unit 11: The Dynamic Crust

Regents Earth Science – Unit 11: The Dynamic Crust
Crustal Changes
Principle of Original Horizontality - sedimentary rocks form in a horizontal position
horizontal
•
any change in the horizontal position is evidence of crustal change
tilted
folded
•
Mountains with sea fossils indicate that the crust has been uplifted
•
Fossils of shallow water animals found at great depths in the oceans indicate
crust “submergence”
faulted
Patterns of Crustal Movements
When plotted on a map, earthquakes, mountains, and volcanoes all occur in the same areas
•
called zones of crustal activity
Earthquakes
Earthquakes are the sudden movement of the Earth's crust
•
most earthquakes occur along plate boundaries
Causes of Earthquakes:
1.
Pressure due to crustal plate movement
2.
Pressure “Unloading” due to the retreat of glaciers
3.
Other sources of pressure
Reference Tables p. 5
Earthquakes
Earthquakes occur at Plate Boundaries:
1.
Divergent - shallow, minor
earthquakes
2.
Convergent - deep, strong
earthquakes
Three Types of Faults Associated with Plate Boundaries:
1.
Normal Fault
2.
Reverse Fault
3.
Strike-Slip
Fault
Transform - shallow,
moderate earthquakes
3.
Faults
1.
Normal Fault - associated with divergent plate boundaries
•
footwall moves up
•
hanging wall moves down
FW
2.
Reverse Fault - associated with convergent plate boundaries
•
footwall moves down
•
hanging wall moves up
•
a low angle reverse fault is called a thrust fault
HW
Faults
3.
Strike-Slip Fault - associated with Transform plate boundaries
Seismic Waves
Fault - break in the rock of the Earth's crust where movement has occurred
Focus - point beneath the Earth's surface where fault movement releases seismic energy
(waves)
Epicenter - point on Earth's surface directly above the focus
Seismic Waves – the energy released by the earthquake
The instrument used to record and measure these waves is called a seismograph
•
The recording made is called a seismogram
Seismic Waves
When an earthquake is recorded, two waves of energy appear
•
there are two kinds of waves the energy travels in:
compression waves and shear (transverse) waves
Types of Seismic Waves:
1.
P-Waves – compression wave
• primary wave – 1st to arrive at a seismic station
• travel through solids and liquids
• travel fast
• particle motion is in the same direction as wave movement
• do little damage
2.
•
•
•
S-Waves – shear wave
secondary wave – 2nd wave to arrive at a seismic station
travel only through solids
travel slow
• particle motion is perpendicular to wave motion
Locating Epicenters
Because seismic waves travel at different speeds, we can determine the distance from an earthquake
•
as 2 objects move at different speeds, the farther they move, the farther they get
from each other
Note: when the speeds the waves travel are plotted, the
difference in the times they arrive can be found, and thus the
distance from their starting point - the epicenter of an
earthquake
Finding Epicenters:
1.
Find the difference in arrival times
of P and S waves on seismograms
from 3 different recording stations
•
•
•
P-wave arrival time = 9 hours 24 minutes
S-wave arrival time = 9 hours 27 minutes
Difference in arrival time = 3 minutes
Locating Epicenters
2.
Find the distance to the epicenter by using the arrival time difference
and the P and S wave Travel Time chart in Reference Tables:
Distance to epicenter = 1800 km
Reference Tables p. 11
3.
Use the map scale to find the radius of a circle that equals the
distance to the epicenter
•
epicenter
3 plots are needed to pinpoint where the epicenter is
difference = 3 minutes
Locating Epicenters
4.
To determine the origin time, find how long the P-wave
took to travel from the epicenter's distance and subtract this
time from the arrival time of the P-wave
1800 km = 3 min., 40 sec P-wave travel time
•
•
P-wave travel time = 3 min 40 sec
P-wave arrival time = 9 hrs. 24 min. (from step 1)
9 hrs. 24 min - 3 min. 40 sec. = 9 hrs. 20 min. 20 sec
•
Origin Time = 9hrs. 20 min. 20 sec.
3 min 40 sec. P-wave
travel time
Earthquakes
Richter Scale - scale used to express the strength (energy released) by and earthquake
•
•
scale ranges from 1 to 10
each increase in magnitude is a ten
times increase in energy
3 min 40 sec. Pwave travel
time
Earthquakes
Mercalli Scale - scale used to show the damage caused by an earthquake
•
scale ranges from
I to XII.
Tsunami
Tsunami - gigantic sea wave caused by an earthquake on the ocean floor
•
•
travel fast: 400-500 mph
50-100 ft. height
Earth's Interior
Seismic waves are used to infer Earth's interior:
•
•
P-wave
P-waves refract (bend) when passing into a
material of different density
S-waves cannot pass through liquids
S-wave
Earth's interior has 4 major zones (based on seismic waves)
1.
Crust - outermost, least dense
2.
Mantle - heat is transferred by convection
3.
Outer Core - metallic, liquid
4.
Inner Core - metallic, most dense
•
•
Outer Core is liquid (S-waves do not pass through)
temperature, pressure, and density increases towards the center
Reference Tables p.10
Earth's Interior
•
Earth's Structure:
•
•
Lithosphere - rigid crust and upper mantle
Asthenosphere - plastic-like layer of the mantle
Volcanoes
Volcano - cone-shaped mountain built of lava and/or volcanic ash
Types of Volcanoes:
1.
Shield - form from lava flows, found at hot spots
2.
Cinder Cone - explosive, found at convergent boundaries
3.
Composite - explosive and non-explosive, found at convergent
boundaries
Volcanoes
•
Location of volcanoes:
1.
Plate Boundaries:
2.
Hot Spots: Hawaiian Islands
•
ocean crust moves over a mantle plume
•
islands form over the plume
•
islands furthest from the plume are oldest
Volcanic Features
•
Igneous Intrusion - molten rock that moves
up/through preexisting rock and cools and
solidifies
Continental Drift
Continental Drift - idea that the continents move over the surface of the Earth like rafts in water
•
proposed by Alfred Wegner in early 1900's
•
continents were once a single large landmass called Pangea
Evidence for Continental Drift
1.
Coastlines of Continents - fit together like a "jig-saw" puzzle
Evidence for Continental Drift
2.
Fossil Clues - fossils of ancient life found on widely
separated continents
•
Mesosaurs - fresh water reptile
•
Glossopteris - ancient seed fern with heavy seeds
(too heavy for wind transport)
3.
Rock Clues - similarities in rock types and mountain ranges
Evidence for Continental Drift
4.
Climate Clues - rocks found today near equator have evidence of glaciation
•
•
5.
•
coral limestone - lived in tropical seas is found
today in New York
coal forms from plants that lived in warm,
swampy environments is found in cold climates
of N. America and Antarctica
Paleomagnetic Clues - Earth's
North Pole appears to wander as
we look back in time with the
continents in their present positions
(A)
If the land masses are shifted back in
time to where the rocks would have
been when they formed, the poles don’t
appear to wander at all (B)
Wegener’s Evidence:
1.
“Jig-Saw Continents”
2.
Matching Mountains/Rock Layers
3.
Fossil Clues
4.
Climate anomalies
5.
Polar Wandering
•
•
Scientists did not take his theory seriously, because he couldn’t explain how
continents could “drift across oceans”
his theory was “shelved” for over 50 years before new evidence was found that
ultimately supported his idea and even expanded on it
Sea Floor Spreading
After WWII, scientists set out to map the ocean floors, and
in the process, found some interesting data that
would explain Wegener’s theory
•
Scientists mapped the ocean floor and noticed it
contained huge mountain ranges, underwater
volcanoes, and trenches
Sea Floor Spreading - principle that oceanic crust spreads
out at mid-ocean ridges
Evidence for Sea Floor Spreading
1.
Age Evidence - as distance from mid-ocean ridge increases, the age of the rock increases
Evidence for Sea Floor Spreading
Magnetic Evidence - magnetic anomalies in
the iron bearing basalt rock of the ocean floor
2.
•
•
rocks that formed during
different time periods were
magnetized to opposite
polar directions, and
matched on opposite sides
of the mid-ocean ridges
3. Iceland –Iceland is located on the Mid-Atlantic Ridge
•
•
new crust is formed by
volcanic eruptions
the islands can be
measured and increase
in size about the same
rate as your fingernails
grow!
Sea Floor Spreading could explain the movement of Wegener’s continental drift and opened the
door to understanding how the continents could have moved and why climates and fossils of
today vary from the past
•
this theory could not explain why the sea floor was split and being pulled and stretched apart
Plate Tectonics
Plate Tectonics - theory that the Earth's surface is composed of about a
dozen rigid plates that carry the continents as they move relative to
one another
•
•
unifies the theories of continental drift and sea-floor
spreading
lithospheric plates (crust and rigid mantle) float on
the asthenosphere (plastic-like layer of the mantle
where heat is transferred by convection)
•
Lithospheric Plates:
•
Reference Tables p.5
•
•
Earth's interior is hot - heat must escape
heat is transferred to the surface by
convection
•
Convection in the Earth's mantle is the
driving force behind plate tectonics
Three Types of Plate Boundaries:
1.
Divergent
2.
Convergent
3.
Transform
Plate Boundaries
1.
Divergent Plate Boundary - where two plate move apart
•
occurs at mid-ocean ridges and rift valleys
ex.: Mid-Atlantic Ridge
2.
Convergent Plate Boundary - where two plate come together/collide
•
subduction - ocean plate (more dense, basalt 3.0g/cm3) sinks underneath a continental plate (less dense, granite 2.7g/cm3)
ex.: Nazca Plate and S. America
3.
Transform Plate Boundaries - two plates slide side horizontally relative to one another
ex.: San Andreas Fault
ex.: India and Asia