Week 4, When the Earth Shakes in Canada... Flashcards
Extensional Regime
Two plates are being pulled apart. Normal faulting.
Mega Thrust Earthquakes
Inter-plate
Shear interface between subducting and overriding plates
M8-9+
Pleoseismic Evidence of a megathrust earthquake
- Coastal marsh soil profiles
- Drowned coastal forests
- Seabed turbidite layers
- Japanese tsunami records
- First Nations oral records
Coastal Marshes
- Peat: deposited when marsh sits above high tide
- Mud: Deposited at low tide
- Sand: brought in by tsunami
Drowned coastal forests
Ghost forests.
Abrupt subsidence in event of earthquake drowns trees in saltwater. Can use dendrochronology to study tree rings to determine date of tree death, thus giving us an idea of when a megathrust earthquake might have occurred.
Seabed turbidite layers
Mud interlayered with sand.
Japanese tsunami records
A tsunami occurs in Japan with no earthquake. Tsunami would take 9 hours to get to Japan, the only earthquake to fit this data is the megathrust that occured in the Cascadia subduction zone. Very accurate data.
First Nations oral records
Spoke of a tsunami where the Pachena Bay people were lost.
Megathrust cycle
Interseismic Period:
- Period between earthquakes.
- Takes place over years.
- We experience all of the effects of evidence seen in the paleoseismic record.
- The toe of North America is dragged down, causing upwelling in Vancouver.
Coseismic Period:
- Happens in a matter of minutes.
- Toe of North America plate jumps up.
Seismology
Study of Earthquakes
Seismometer
Instrument that detects vibrations of earth to measure earthquakes.
Seismograph
Recording instrument to record what is detected from seismometer.
Wave Properties, Function of Position:
- Amplitude (A): Maximum value
- Wavelength: Distance of one wave cycle
- Velocity (V): Speed at which wave moves
Wave Properties, Function of Time:
- Period (T): Measured in seconds of one cycle
- Frequency: Distance travelled per time
Body Waves
Propogate through interior of earth.
Compression
Shear
