Earthquakes and Tsunamis Flashcards
What are the major fault types?
- Normal fault
- Reverse fault
- Thrust fault
- Left lateral strike-slip fault
- Right lateral strike-slip fault
Normal fault
Hanging wall is down relative to the footwall
Reverse fault
Hanging wall is up relative to foot wall at a high angle
Thrust fault
Hanging wall is up relative to footwall at a low angle
Faults occur because directed stress builds up in rocks:
- Compression
- Tension
- Shear
Motion and usual location of compression
Squeezing, convergent plate boundaries
Motion and usual location of tension
Stretching, divergent plate boundaries
Motion of shear
Slipping along a plane parallel to the stress
The accumulation of stress in a rock produces:
Strain or deformation
Strain takes place in 3 stages:
- Elastic deformation
- Ductile deformation
- Brittle deformation
What is elastic deformation?
Fully reversible (stretching the spring a little and it springs back). When stress is proportional to strain (Hooke’s Law of Elasticity)
What is ductile deformation?
Irreversible (stretching the spring too much and it won’t go back to its original shape). Folding, change in volume of rock.
What is brittle deformation?
Fracture (stretching the spring so much it breaks). Rock breaks.
What are faults?
Planar fractures in rocks, that vary in size and scale, where the rocks on either side have moved.
Earthquakes are caused by:
movement along faults
Elastic Rebound Theory
Friction exists along the fault plane, so the rock on either side of the fault resist movement
- Stress added
- Rocks deform, store energy
- Rocks break, release energy (earthquake)
- Rocks rebound to undeformed shape
Most earthquake foci occur at depths <15km in the crust. Why don’t earthquakes occur in the mantle?
The mantle behaves like ductile plastic because it can flow, increased depth = increased heat and pressure, results in plastic characteristics
Where do the deepest earthquakes occur?
Convergent boundaries and subduction zones, in addition to shallow/intermediate as well
Shallow, intermediate, and deep earthquakes can happen at subduction zones because of
the push and pull of subduction zones = earthquakes
Transform and divergent boundaries are predominantly associated with
shallow earthquakes
How do we detect earthquakes?
Seismic waves (vibrations) are conducted through the Earth, which allows for detection and triangulation