Earth's Internal Structure: Earthquakes and Faults (2.2.2) Flashcards
What are earthquakes?
- Sudden release of energy in Earth’s crust, creates seismic waves. (Wikipedia)
- Most caused by brittle failure of rock in Earth’s upper crust.
- Generate seismic waves, propagate in all directions radially away from source.
- Not randomly distributed.
What is the epicentre?
Projection of rupture point at surface.
What is the hypocentre (focus)?
True location of rupture.
What generates earthquakes?
- Vast majority caused by movements on faults.
- Faults: planar fractures which relative movement takes place to relieve stresses in Earth’s brittle outer layer.
What are the three fundamental types of faults?
- Normal faults: from extension, cause crustal thinning.
- Reverse faults/thrusts: from compression and crustal thickening.
- Strike-slip faults: from blocks moving laterally past each other from horizontal shearing forces.
What are faults?
Planar fractures, relative movement takes place.
What are joints?
Fractures in rocks, no relative movement. Don’t give rise to significant earthquakes.
What is a fault plane?
Plane of sliding along fault.
What is a fault scarp?
Exposed portion of fault plane.
What is a fault trace?
Intersection of fault with surface.
What is a dipping fault?
- Hanging wall block positioned over fault.
- Foot wall block positioned under.
- Hanging wall elevated or subsided compared to foot wall.
Normal faults drop ? rocks ? against ? rocks, omit ?
1) younger
2) drop
3) older
4) stratigraphy
?/thrust faults push ? rocks ? over ? rocks, repeat ?
1) reverse
2) older
3) younger
4) stratigraphy
What are strike-slip faults?
- Show little/no vertical motion along fault plane.
- Two sides move sideways relative to each other.
- Dextral fault (right-handed).
- Sinistral fault (left-handed).
What do faults create and determine?
Landforms.
- Mountain ranges formed by compression, built up of thrust layers.
- Rift valleys/basins formed by normal faults, formed by extension.
