Week 5 Lecture: Earthquakes Flashcards
List the components of an earthquake at its center
- Eppicenter
- Focus
- Fault Plane
- Seismic Waves
- Fault Scarp
- Fault Trace
Where are the Epicenter and Focus located in relation to the surface of the Earth?
Focus: underground centerpoint on the fault plane where the earthquake originates
Epicenter: projected surface point directly above the focus
What kind of fault is the San Andreas Fault?
Transform Fault
Explain the Elastic Rebound Theory
Extreme shear stress builds on either side of a fault. If external rigidity is exceeded, then a rupture along the fault line releases energy in a seismic wave before the rocks snap back to original position.
List some internal Seismic Energy sources
- Earthquake faulting
- Buried Explosions
- Magma movements
List some external Seismic Energy sources
- wind
- waves
- meteorite impacts
What are the three stages of an earthquake
- Foreshock
- Mainshock
- Aftershock
What are the two subcategories of Seismic Waves?
- Body Waves
- Surface Waves
What are the two subcategories of Body Waves?
- Primary (P-waves)
- Secondary (S-waves)
What are the two subcategories of Surface Waves?
- Love Waves
- Rayleigh Waves
Differentiate Body and Surface Waves
Body waves travel through the Earth’s interior and spread outward from focus point in all directions
Surface waves travel in the crust and on the surface and spread outward from the epicenter
List the order in which each wave occurs during an earthquake
- P-Waves
- S-Waves
- Surface Waves
Describe and compare P and S-waves
P-waves:
- are compression waves in which rocks vibrate back and forth
- travel at 4-7 km/sec
- can also occur in liquids and gases
S-waves
- travel in shearing motion where rocks vibrate perpendicular to direction of wave
- travel at 2 -5 km/sec
- cannot occur in liquids and gases
Do Body or Surface waves cause more damage?
Surface waves cause more damage (Love and Raleigh waves travel together)
Describe and compare Love and Rayleigh waves
Love waves:
- side to side motion in horizontal plane
- perpendicular to direction of wave
Rayleigh waves:
- up and down motion
- opposite to direction of wave propagation
How does Lithology affect the speed of seismic waves?
the velocities of seismic waves are slower through loose and uncompact soil/rock and faster through hard/compact rock
How is an earthquake epicenter located?
- The time interval between arrival of P-wave and S-waves is measured
- Three seismometers measuring this interval are used to triangulate the position
How does the Richter scale work?
- A vertical scale of interval between S and P-waves (in seconds) is placed on one side
- A vertical scale of amplitude (in mm) is placed on the other side
- In between the two scales, a vertical Richter magnitude scale is placed
- A line is drawn b/w the two outer scales, and the resulting line intercept on the Richter scale is read
The Richter scale is logarithmic
Just remember that
Describe the action of the plates in the 2011 Japan Earthquake
- Earthquake was result of thrust faulting near convergent plate boundary of three plates
- Pacific plate subducted under both Eurasian Plate and Phillipine Plate
- Phillipine also was subducting under Eurasian Plate
What was the slip length and resulting water uplift that caused a tsunami during the Japan Earthquake?
- 18m slip length
- 4m uplift
What unit of earthquake measurement is more common now than Richter Scale?
Moment magnitude (Mw)
What is the equation for the Moment magnitude scale?
Moment = rigidity x area x slip
What earthquake scale uses 12 stages of perception
The Modified Mercalli Intensity scale
List and describe the two categories of earthquake effects
Primary effects: associated with ground movement during earthquake and seismic energy (Building collapse or damage)
Secondary effects: hazards related to response to primary effects (landslides, liquifaction etc.)
Explain Liquefaction effects
- saturated soil turns into quicksand during earthquake
- sediments flow like fluids
- buildings etc sink and tip over
How does liquefaction occur?
water in sediment completely surrounds all grains and eliminates grain to grain contact
Describe the steps of a Tsunami
- underwater earthquake causes a break in sea floor that pushes water up
- wave generated of very long wavelength
- as water gets shallower, wave slows down and amplitude increases sharply
How fast do tsunami waves travel in open ocean?
600 to 700 km/hr
Describe two scientific methods of Earthquake Prediction?
- construction of seismic risk maps based on history, intensity, and likelihood of past earthquakes
- consideration of tectonic plate boundaries and major fault zones
List some ways an Earthquake can be predicted
- probability map
- seismic gap (areas where earthquake hasn’t happened in a while)
- land elevation and tilting
- well water fluctuations
- bizarre animal behaviour
- foreshocks
List and describe 3 factors of Earthquake Effects
Intrinsic factors: magnitude/type of earthquake, potential for tsunami etc
Geologic factors: underlying soil or bedrock etc
Societal factors: quality of construction, emergency response, population preparedness
