Seismicity: Earthquakes And Tsunamis (hazards) Flashcards
Divergent-constructive
Mid-ocean ridges - tensional forces associated with spreading with faulting and rifting
Convergent continental - oceanic destructive margins
Ocean trenches and island arcs - compressive forces associated with the subduction of one plate below another
Convergent continental - continental collision zones
Collision zones - compressive forces associated with the grinding together of plates carrying continental crust
Conservative margins
Conservative plate margins - shearing forces associated with the intermittent movement of one plate past another
Intro plate locations
-presence of old fault lines
-collapse of old mine workings
-the extraction of gas and oil from rocks deep underground
What causes earthquakes?
The release of built-up pressure inside the earths crust, in the form of seismic waves. This occurs when rock fractures and allows the plates to unlock and so move.
What are the different types of earthquakes?
Shallow focus quakes
Deep focus quakes
Which earthquakes is more common?
Shallow focus quakes are more common
Why are shallow focus quakes more common?
Because they happen at all plate boundaries
What are the different types of faults?
-strike-slip faults
-normal faults
-reverse faults
Strike slip faults
Indicate rocks are sliding past each other horizontally, with little to no vertical movement.
Give an example of a strike-slip faults
The San Andreas and Anatolian faults
Normal faults
The faults create space. Two blocks of crust pull apart, stretching the crust into a valley.
Give an example of a normal fault
East African rift zone
Reverse faults
Also called thrust faults, they slide one block of crust on top of another, commonly found in collision zones.
Give an example of a reverse faults
The Himalayas
How do we measure earthquakes?
- Richter scale
- Moment magnitude scale
- Mercalli scale
Richter scale
Uses logarithmic scale to measure magnitude.
Uses amplitude of seismic waves as an indicator of energy released
10 fold rise in wave amplitude for every point on the scale, but the energy released increases 30x with every 1 point increase.
Moment magnitude scale
Looks at amount of ground movement rather than just amplitude
Rock rigidity, area of fault surface, amount of movement on fault are all factored in
Logarithmic like Richter
Most accurate for large quakes
Mercalli scale
Measures intensity of shaking which results in effects of earthquakes
Ranked on subjective scale from 1-12
