Transcript Dynamic Earth

Dynamic Earth
Topics:
-Earth’s Interior
-Continental Drift
-Seafloor spreading
-Plate Tectonics
-Earthquakes & Epicenters
Earth’s Interior
As depth increases so does:
-pressure
-temperature
-density
Earth’s Interior
• Crust
- outer thin rock layer
– Mostly silicon and magnesium
Oceanic: thin; basalt rock (dense)
Continental: thick, granite rock (less dense)
Earth’s Interior
• Mantle
– thickest layer of plastic molten rock
– Mostly silicon and magnesium
asthenosphere: upper part; where convection
currents are found
Earth’s Interior
• Outer core
-iron and nickel
-liquid due to intense heat
-S waves cannot travel through
• Inner core
-iron and nickel
-solid due to intense pressure
Continental Drift
• Continents were once joined together
• Evidence:
-jigsaw fit of continental coastlines
-matching geologic features (Mts) across
continents
-fossils of tropical plants found in
continents now in polar regions
-fossils of the same species found across
oceans
Seafloor spreading
• Age of rocks at mid ocean ridge increase
as you move away from ridge
• Magnetic mineral alignment in basalt
(igneous rock) shows poles reversal
forms mirror image on both sides of
MOR
Plate Tectonics
• Driven by convection currents in mantle
caused by Density Differences:
heat from Earth’s interior causes hot, less
dense magma to rise and cool, more
dense magma to sink
• Lithospheric plates slide along with the moving
magma
• Plate boundary: where one plate makes
contact with another
earthquakes and volcanoes occur at zones of
crustal activity (boundaries)
Converging Plate Boundary
• Plates collide 
• Continent to Continent: mountain building
-uplift of rock: oceanic fossils seen on mts
• Continent to oceanic: dense oceanic crust
sink below continental crust
-subduction zone
-volcanoes form on continent
Diverging Plate Boundary
• Plates move apart
• Ex: mid ocean ridge
• New crust is formed
Transform Plate Boundary
• Plates slide past each other
• Cause rocks to fault (crack)
-produces Earthquakes
Hot Spots
• Form volcanic islands
(Hawaii)
• Stationary plume of rising
magma
• As lithospheric plate moves
over hot spot, magma
pushes through crust
• Islands older the further
away from hot spot
Earthquakes & Epicenters
• Stress builds up and causes rock to shift
• Energy released as seismic waves:
-P Wave: travels quickly through solids
and liquid layers of Earth
-S Wave: travels slower though solids but
NOT liquid layer (outer core)
Locating the Epicenter
• One seismic station gives you its distance
from epicenter but no direction
• 3 seismic stations are required to locate
Finding difference in arrival time
• Given the arrival times of each wave, use
their difference to determine distance
traveled
The distance from Albany, New York, to the epicenter
of an earthquake is 5600 km. Approximately how
much longer did it take for the S-wave to arrive at
Albany than the P-wave?
a. 4 minutes and 20 seconds
b. 16 minutes and 10 seconds
c. 9 minutes and 0 seconds
d. 7 minutes and 10 seconds
Finding Travel Time/distance
• Given distance from epicenter, you can find how long it
takes a P or S wave to travel to that seismic station
• Or you can find the distance the wave traveled based on
how long it took the wave to travel there
Approximately how long does an earthquake P-wave take to travel the first
6500 kilometers after the earthquake occurs?
6.5 min
10.0 min
8.0 min
18.5 min
In 8 minutes, an earthquake P-wave travels a total distance of
2,100 km
6,600 km
4,700 km
11,300 km
Calculating Arrival Time
• If you know how long it takes one wave
type to travel a given distance, you can
find out
-the time the earthquake happened
or
-the arrival of the other wave type
A seismic station recorded an
earthquake with an epicenter distance
of 4,000 kilometers. If the origin time
of the earthquake was 11:00 a.m., what
time did the P-wave arrive at the
seismic station?
10:53 a.m.
11:05 a.m.
11:07 a.m.
11:12 a.m.
An earthquake's P-wave arrived at a
seismograph station at 02 hours 40
minutes 00 seconds. The earthquake's
S-wave arrived at the same station 2
minutes later. What is the approximate
distance from the seismograph station
to the epicenter of the earthquake?
1,100 km
2,400 km
3,100 km
4,000 km
• An earthquake occurs at 12:02 p.m. A
seismic station records the first Swave at 12:19 p.m. Which set of data
shows the approximate arrival time of
the first P-wave and the distance to the
epicenter?
a. 12:11:25 p.m. and 4000 km
b. 12:11:25 p.m. and 6000 km
c. 12:19:40 p.m. and 4000 km
d. 12:19:40 p.m. and 6000 km
Tsunami
• Underwater Earthquake pushes water
onto shore
• Wave height grows at it approaches shore