Flashcards in Lecture #7 - Earthquakes Deck (49):
What are quakes the result of?
Rupture of rocks along a fault line
How is the energy of a quake released as?
What is the difference between the Epicentre and the Focus?
Epicentre is where the earthquake actually happens below ground
Focus is the place on the surface directly above the epicentre
How do we measure earthquakes?
Moment Magnitude Scale
What is the Moment magnitude scale determined by?
-amount of movement along a fault
-The elasticity of the crust
What is the Modified Mercalli Intensity Scale?
- Qualitative scale based on the damage to structures and the affect on people.
What causes the sudden movement along the fault ?
-Stress builds up, causing inconsistent movement in the fault.
-When stress is greater, it causes the fault to jump forward, causing and earthquake
Where to seismic wave originate?
At the focus
What are Blind faults?
Faults located below the surface
-aka can't see em
What are the 2 types of faults based on the directions of the displacement of rock or sediment?
1. Strike -Slip fault
2. Dip Slip Fault
What are the 3 types of dip slip faults?
What are the 3 categories that faults can fall into?
2. Potentially active
What is a Tectonic Creep?
The slow movement of rock or sediment along fracture caused by stress
In what places to seismic waves travel?
Through the body of the earth and along the surface
What are body waves?
Include P and S waves
What are P waves?
-push pull motion
-Can travel through solid and liquids
What are S waves?
-Up and down motion
-Can only travel through solids
What are surface waves?
Seismic waves that form when P and S waves reach earths surface and then move along it
-move slower than body waves
What are some factors that determine what shaking people feel from ta quake?
-Distance to epicentre
-Direction of the rupture
-Soil and rock type
What happens to shaking as you increase distance form the epicentre?
How do you calculate where the epicentre is?
-measured n 3 different seismographs
-where they all intercept is where it is
What happens to the waves as they spread outwards?
They become less intense
What is the relationship between focal depth and shaking?
As focal depth increases, the shaking decreases
what is directivity?
Quake energy is focused in the direction f the rupture
relationship between ground motion and hetero/homogeneous soils?
Homogenouse can transmit energy more quickly
Heterogenous slows down the energy
-mountians can also slow down the structure
What is Amplification?
An increase in ground motion during an earthquake
Can 2 quakes at the same magnitude have the same impact?
Depending on where they are they can have very different impacts
What is the Earthquake cycle?
Hypothesis that explains successive earthquakes on a fault
-Strain drops abruptly after an earthquake and then slowly builds back up
What are the 3 stages in a typical cycle?
- inactive period
-Strain produces minor
-foreshock prior to the big shock
What is a fore shock?
a small to moderate quake that occurs before and in the same general area as the main shock
What are plate boundary earthquakes?
Quakes that occur o faults separating lithospheric plates
- can have strike slip, thrust and normal
What is a strike slip quakes?
occur along transform faults where plates slide horizontally past each other
What is a thrust quake?
Occur on faults that separate converging plates
What is normal fault quake?
occur on faults associated with divergent plate boundaries
What are interpolate quakes?
A quake on a fault in the interior of a continent.
-far from a plate boundary
What are the 2 active interpolate zones?
Mississippi River valley
St Lawrence River valley
What are the 2 regions in the US that could have a high M value?
What are some Primary effects of quakes?
What are some Secondary effects?
-Land level change
What is a ground rupture
displacement along faults causes cracks in the surface
What is a Fault Scarp?
A linear escarpment at earth surface formed by movement along a fault during a quake
What is Liquefaction?
The transformation of water saturated sediment from solid to liquid
What are landslides?
Ground motion produced by a quake can cause rock and sediment to move downslope
How can quakes cause fires?
the sock can sever power lines and gas lines which can catch on fire
What are the natural service functions of quakes?
-Provide pathways for the downward flow of surface water
-Can channel water to surface discharge points
-new material resources can be exposed
How can humans produce quakes?
-Weight of damns can create new faults
-Injecting liquid waste into the earth
-Testing nuclear weapons
How do we estimate seismic risk?
By using hazard maps
What are the 4 precursors to quakes?
1. The pattern and frequency of earthquakes (based on foreshocks and micro earthquake)
2. Land level changes
3. Seismic Gaps
4. Physical and chemical changes