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Transcript of Earthquakes 3
Image running 2 wooden boards against one another. Friction between the boards may temporarily slow their motion, but rough edges break off and motion occurs at various places alone the plane.
- Lithosperic plates moving past one another are slowed by friction.
- This breaking action stresses the rock along the boundry.
- When the rocks exceed their ability to withstand it refered to as their strenth the rocks rupture along a fault A fault is a fracture or a fracture system where
rocks have been displaced.
The long term movement is called the slip rate and is often measured in mm per year.
When a rupture begins it starts at the focus and then propogates up, down and lattery along the fault plane during the earthquake.
The sudden rupture of rocks create shock waves called seismic waves which can shake the ground
- Faults are therefore seismic sources
- First steps in identifying earthquakes Types of Faults Strike slip Dip slip Blocks of earth move in a horizonal motion Blocks of earth move mainly in a horizonal motion Normal Fault Reverse Fault/ Thrust Fault Footwalls and Hanging walls -Term came from Miners
- Imageing that the fault plane is the floor of a mine
and that you are walking down the into the earth.
- The block of earth bellow your feet is the footwall and
the block above your head is the hanging wall.
If the hanging wall is moving upwards to the footwall it is called a thrust fault
If the hanging wall is moving downwards to the footwall it is called a normal fault Because it just makes sence Tectonic Creep Some active faults exibit gradual movement along a fault which is not acompanied by felt earthquakes Local Geological Conditions and Earthquakes Liquification - During Earthquakes, intense shaking can cause water saturated sediment to change rapidly from a solid to liquid
- Like quick sand
- Can cause entire buildings to fall over or submerge Landslides - Earthquakes are the largest cause of lanslides
- 1970 Peru killed 20000 to 70000 people Fire
- Shaking of the ground can break electrical lines and natural gas lines
- The threat is increased because roads can be blocked and fire fighting equipement can be damaged Disease
- Outbreaks of disease are sometimes associated with large earthquakes.
- Caused by a loss of sanitation and housing
- Disruption of public health survices
- Diarrhea in Haiti