Chapter 3 Flashcards
- Plate Tectonics
the theory that states that the Earth’s crust is separated into plates or pieces that move.
- What are plate boundaries?
Plate boundaries or margins are where plates meet. They are important because this is where most geological processes and many hazards are found.
- 3 types of plate boundaries
Divergent
Transform
Convergent
Divergent Plate Boundary Example
The Mid-Atlantic Ridge that divides iceland is the boundary between the North American and Eurasian plates.
Convergent Plate Boundary Example
Off the West Coast of B.C. : Where the Juan de Fuca Plate subducts under the North American Plate.
Transform Plate Boundary Example
The San Andreas fault zone is a transform boundary between two tectonic plates: the North American plate and the Pacific plate
- Give examples of all 3 types of plate boundaries
CONVERGENT - West Coast of B.C. : Where the Juan de Fuca Plate subducts under the North American Plate.
DIVERGENT: The Mid-Atlantic Ridge dividing Iceland is the plate boundary between the North American Plate and the Eurasian Plate
TRANSFORM: The San Andreas fault zone is a transform boundary between two tectonic plates: the North American plate and the Pacific plate
- Earthquake
A shaking of the ground caused by a release of energy inside the Earth.
- Where do most Earthquakes occur?
At plate margins. Most occur at convergent and transform margins.
Things to list on a wave diagram (draw)
Crest Trough Wavelength Waveheight Amplitude (define: Frequency, Period )
Period
How long it takes for a wave to travel one wavelength distance.
Frequency
Frequency is the number of waves to pass a given point in a given amount of time.
Wavelength
The distance between two corresponding points on any two successive waves. (i.e. distance between adjacent crests or troughs. )
Amplitude
Amplitude is the distance between the top or bottom of the wave and its median point.
- What is a P wave?
- a seismic wave
- faster speed (8km/sec)
- causes objects to move back and forth horizontally.
- What is an S wave?
- a seismic wave
- slower speed (5km/sec)
- cause objects to move up and down.
- Body wave
An energy wave that travels through the Earth.
- Surface wave
An energy wave that travels along the surface of the Earth
- How do the velocities of P and S waves differ from one another?
P wave: travels at a faster speed (8km/sec) S wave: travels at a slow speed (5km/sec)
- Seismograph
A sensitive instrument used to measure ground motion.
- How does a seismograph work (for P waves)?
A - a frame fixed to the ground. (this part will move with the ground)
B - a heavy weight connected to the frame. This part will not move with the ground.
C - On the weight is a pen that will not move in an earthquake.
On the frame is a writing surface that will move. So far this type of seismograph will only detect ‘P’ waves.
- How does a seismograph (for S waves)?
See photo This type of seismograph will detect S waves.
- Fault
A break in the Earth’s crust along which there is movement.
- Normal Fault
caused by tensional stress
- Reverse Fault
caused by compressive stress (see photo)
- Strike-Slip Fault
Caused by shear stress. Can be left lateral or right lateral. (see photo)
Strain
Strain refers to how an object responds to stress.
Stress
Stress refers to the unequal application of force.
There are three types of stress: compressive, tensional, shear
- Difference between stress and strain.
Stress refers to the unequal application of force.
Strain refers to how an object responds to stress.
Under stress a rock body will either bend (fold) or break. (faults)
- What factors affect stress and strain in a rock body?
Stress and strain in a rocky body are affected by:
- COMPOSITION: the number and type of different minerals
- TEXTURE: The size, shape and packing
- STRUCTURE: The presence of faults, fractures or bedding planes
COMPOSITION (as it relates to stress and strain)
the number and type of different minerals
TEXTURE (as it relates to stress and strain)
The size, shape and packing
STRUCTURE (as it relates to stress and strain)
The presence of faults, fractures or bedding planes
- Elastic Rebound Theory (DRAW)
- Elastic Rebound Theory (DRAW Diagram 2)
- Elastic Bound Theory Example Explained
At A the leading edge of North America is being pushed up because of compressive stress at this convergent plate margin
At B the Juan de Fuca plate and North America plate are locked together. When the rock along this surface breaks and earthquakes will occur as the plates move.
This also means that the rock at A will respond elastically and return to its original shape.
Along the west coast of Vancouver Island falling sea level will be placed by a sudden rise in sea level as the land drops.
- What is the Mercalli Intensity Scale?
This scale includes information about magnitude and a measure of the damage done. This intensity scale differs from the magnitude scale which is related to the energy released by an earthquake.
- What are the limitations of the Mercalli Intensity Scale?
The limit to this scale is that it may rely only on local features that are not always found everywhere. For example, not all houses are built the same everywhere.
- Magnitude scale
A scale based on earthquake wave amplitude. Every interval increases in magnitude by 10 times. (image)
- What is an Earthquake Environmental Effects (EEE) Scale?
This scale includes the effects an earthquake may have on the natural environment. In particular in regards to changes observed along a fault.
ROCK COMPOSITION (earthquake energy)
Igneous intrusive (solid, coarse, crystaline) rock and metamorphic rock transmits energy better than sedimentary rock
ROCK TEMPERATURE (earthquake energy)
Rocks that are colder, and therefore more solid, transfmit earthquake energy better than a hotter, less solid rock.
ROCK STRUCTURE (earthquake energy)
- STRUCTURE: Rocks with fewer weaknesses such as faults, fratures and bedding planes will transmit energy better than rocks with these weaknesses
- How does bedrock composition, structure and temperature affect earthquake energy?
- COMPOSITION: Igneous intrusive (solid, coarse, crystaline) rock and metamorphic rock transmits energy better than sedimentary rock
- STRUCTURE: Rocks with fewer weaknesses such as faults, fratures and bedding planes will transmit energy better than rocks with these weaknesses
- TEMPERATURE: Rocks that are colder, and therefore more solid, transfmit earthquake energy better than a hotter, less solid rock.
- How does liquefacton occur?
Soil liquefaction is when a saturated or partially saturated deposit substantially loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress condition, in which material that is ordinarily a solid behaves like a liquid.
Pores in sediment near the surface may fill with water.
Sometimes there is too much water and water pressure increases, forcing them apart. This creates a less stable deposit that is able to flow or move like a fluid.
Ground motion (vibration) during an earthquake can force water in the ground to move. This creates places of higher and low pressure underground.
Where pressure is high, sediment grains are forced apart and the ground begins to flow. The ground is now unable to support significant weight.
- What is a Quick Clay? (PART 1)
Quick clay is a clay deposit.
When clay minerals are deposited they will sometimes include other elements within their structure.
When deposition takes place in sea water Sodium (Na+1) is often included. This creates a very loosely organized, low density clay mineral structure in this deposit.
(SEE PHOTO)
As long as this deposit remains in this “way” it is stable.
What is Quick Clay (PART 2)
However, these deposits can be exposed above sea level where they can be affected by freshwater which will remove the sodium. This makes for a much less stable clay deposit.
Sudden ground motion associated with an Earthquake can cause these deposits to fall downhill or fail.
- Explain the events of Jan 9, 1965 near Hope, BC.
- A large landslide took place in the Coast Mountains following a minor earthquake
- A large mass of rock fell from Johnson’s Peak
- The exposed igneous rock and metamorphic rock was weathered, unstable and sitting at a steep incline
- Wet, water saturated conditions at the time and an earthquake in the area triggered this event.
Terrane
A body of rock formed at one location and moved to another by plate tectonics.
Strain
Strain refers to how an object responds to stress.
Porosity
the space inside a rock or sedimentary deposit
Permeability
A measure of how well connected the pore are.
Clay mineral
A clay mineral is a sheet/phyto silicate mineral that has a very high surface area to volume ratio. It is made of flat, sheet like grains. The large surface areas are also electrically charged. This allows clay minerals to store other electrically charged atoms or molecules on their surfaces.
Quick Clay (pre)
Quick clay is a clay deposit. When clay minerals are deposited they will sometimes include other elements within their structure. When deposition takes place in sea water Sodium (Na+1) is often included. This creates a very loosely organized, low density clay mineral structure in this deposit. (SEE PHOTO! DRAW DIAGRAM!) As long as this deposit remains in this “way” it is stable.
Quick Clay (after set up)
However, these deposits can be exposed above sea level where they can be affected by freshwater which will remove the sodium. This makes for a much less stable clay deposit. Sudden ground motion associated with an Earthquake can cause these deposits to fall downhill or fail.
