New Zealand Earthquake

1
New Zealand Earthquake

• M 6.3 earthquake
• Shallow epicenter 2-3 miles
• Close to Christchurch, city of 370,000
• After shock to the September 4th M 7.1

2
What is the composition of lava formed on oceanic
crust?

• High percentages Fe, Mg
• Low percentages Si, O

3
Describe a convergent plate boundary
4
What is the source of the lava that forms oceanic
crust?

• the mantle or asthenosphere

5
What is the composition of lava associated with
continental crust?

• High percentages Si, O
• Low percentages Fe, Mg

6
The Theory of Plate Tectonics

• Based on two hypotheses
• Continental Drift
• Seafloor spreading

7
Explain the development of the theory of plate
tectonics in terms of the scientific method.
8
The Scientific Method
Observation of data or information
One or more ideas, statements or
questions Single or multiple hypotheses
Collection of data
Not accepted
Hypothesis
More Data
Theory
9
Continental drift hypothesis evidence?

• Proposed in 1911
• All evidence found on the continents
• Mechanism for moving the continents was not known

10
Continental Drift Hypothesis

• Alfred Wegener proposed the hypothesis of
  continental drift in 1911
• He gathered information from many different
  sources and used it as evidence for his hypothesis

11
Continental Drift Hypothesis

• Fit of the continents
• Fossil evidence
• Ancient mountain ranges
• Past climate evidence

Swamps formed in tropical regions
Glaciers formed at the south pole
12

• The continental drift hypothesis proposes that
  the continents were assembled to form the super
  continent Pangaea.
• Moved through time

320
13
Fit of Continents

• Antonio Snider-Pelligrini (1858), a geographer
  cut out a map of Africa and South America
  suggesting they were connected at one time
• Other physical evidence based on observation was
  used by Wegener

14
Fossil Evidence

• Similar terrestrial species were found on many
  continents now separated by oceans.
• Information collected by paleontologists

15
Ancient Mountain Ranges
The same sequence of rocks is found in North
America, Great Brittan, and Norway. The pattern
does not make sense with the continents in their
current configuration.
16
The Appalachian Mountains
Swamps
300 million years ago
17
Evidence of Ancient Glaciers

• Glaciers carve the rock as they move.
• Scientists can determine the direction of
  movement (notice the direction of movement noted
  in South America)
• As South America sits today, the pattern would
  not make sense. (glaciers do not move from sea
  level to higher elevations)

18
Lack of mechanism to explain continental movement.

• Evidence implied that the continents were at one
  time assembled
• Wegeners idea was not accepted by the scientific
  community because he could not explain how the
  continents moved
• With advances in technology, new information was
  gathered in association with WWII

19
Exploration of the Ocean Basins

• What information do you know regarding the
  seafloor that may be used to help understand the
  hypothesis of seafloor spreading?

20
Exploration of the Ocean Basins

• Seafloor features
• Composition of the seafloor
• Age of the seafloor
• Hot spots
• Seismicity
• Paleomagnetic pattern produced on the seafloor

21
Exploration of Ocean Basins
Ocean basins contain a variety of landforms not
discovered until WW II.
22
Support
Seafloor features were discovered using sonar.
426

• Echo sounding was used to map the seafloor

23
Seafloor features

• Mid-oceanic ridges
• Trenches
• Volcanism adjacent to trenches
• Seamounts
• Fracture zones

24
Oceanic crust is composed of volcanic rock.
Pillow basalts

• Basalt is volcanic rock with a mafic composition.
• Higher percentages of iron and magnesium, lower
  percentages of silicon and oxygen.

25
Age of Ocean Crust

• Youngest at ridge
• Progressively older away from ridge
• Mirror image across the ridge

26
(No Transcript)
27
Seismicity

• Earthquakes are concentrated at what is currently
  known as plate boundaries.
• Explain why there are broad bands of seismicity
  associated with some areas.

28
(No Transcript)
29
Earths Magnetic Field
Bipolar acts like a bar magnet
30
(No Transcript)
31
(No Transcript)
32
Requirements for a magnetic field

• An interior region of electrically conducting
  fluid such as molten metal.
• Convection in that layer of fluid.
• At least moderately rapid rotation.

33
A compass has a different declination depending
on the location on the Earths surface
34
Earths Magnetic Field

• Strength varies with location
• Red- stronger
• Blue weaker

35
Iron-rich rocks are magnetized as they cool to
the current magnetic field.

• Basalt iron rich volcanic rock oceanic crust

36
Paleomagnetic pattern across the mid-oceanic ridge
Negative anomalies reverse polarities
Positive anomalies normal polarities
Mirror image across the ridge and correlative
with age
37
Polar Reversals

• Correlated to time
• Scientists dated iron-rich volcanic rocks on land
  
• Developed technology to measure the paleomagnetic
  reading

38
Polar Reversals

• Timescale of polar reversals
• Possibly related to flow in the outer core

39
Paleomagnetic Evidence

• Positive and negative recordings of the oceanic
  crust create a symmetrical pattern across the
  mid-oceanic trench

40
Seafloor Spreading

• In the 1963, Harry Hess developed the idea of
  seafloor spreading to explain the seafloors
  formation
• Continental movement is the result of ocean floor
  movement

41
Seafloor Spreading

• Mafic lava is extruded along the mid-oceanic
  ridge to produce ocean floor.
• New material is added, the cooler material is
  split and is pushed away from the ridge

42
Driving Mechanisms
Convection cells within the mantle
Push
Pushing at the mid-oceanic ridges
Pull
Pulling at the subduction zones
Convection
43
The theory of plate tectonics

• Explains that the Earths lithosphere is broken
  into distinct units that move as a coherent
  package. Where the tectonic plates meet, produces
  distinct physical characteristics on the Earths
  surface.

44
The Scientific Method
Observation of data or information
Associated with the continents
Continental Drift Hypothesis
Collection of data
Not accepted
Ocean basins
Seafloor Spreading Hypothesis
Mechanism for plate movement
key
Theory of Plate Tectonics
45
Information to understand

• The evidence used by Wegener to describe the
  continental drift hypothesis.
• The evidence associated with technology that was
  used to collect information about ocean basins.
• The hypothesis of seafloor spreading
• The accepted tectonic plate driving mechanism.

46
Earthquakes and volcanoes outline the tectonic
plate boundaries