Tectonics - Earthquakes Flashcards
Continental crust
20-60km thick
permanent
older
relatively less dense
Oceanic crust
Thinner
formed at mid ocean ridges
Destroyed at subduction zones
Relatively more dense
Divergent/ constructive plate boundaries
Two oceanic plates move apart and magma rises to fill the gap, causing the creation of new oceanic crust
E.g - mid Atlantic ridge : S.American plate and African plate
New oceanic crust being formed at the bottom of the ocean as plates pull apart is called sea floor spreading
Convergent/ destructive plate boundaries
When oceanic and continental plates move towards each other and collide. The oceanic plate is heavier so it sinks beneath the continental plate (subduction) back into the mantle
E.g- Nazca plate (oceanic) and S.American plate (continental)
Fold mountains
When two continental plates collide (collision boundary), they are too light for either to sink.
This makes part of the crust fold, resulting in the formation of mountains and fold mountains. No volcanoes formed but earthquakes are
E.g- Indo-Australian plate and Eurasian plate
Conservative boundaries
Two plates move sideways against eachother.
Volcanic activity does not occur and crust is neither created nor destroyed, but the friction between the two plates can cause large earthquakes
E.g- San Andreas fault where pacific and North American plate slide against eachother
Earthquakes
Occur when moving plates get stuck br friction and pressure builds up until it is suddenly released, sending shock waves to the surface
Focus
The exact place beneath where an earthquake happened
Epicenter
The point on the surface directly above the focus
Mercalli scale
Gives an indication of earthquake intensity determined by the effects on people, buildings and landscape
Magnitude determined by amount of energy released, depth of focus and distance from epicenter
Has 12 levels
Richter scale
Based on measurements made by seismographs, making comparisons of different earthquakes easier.
Scale is logarithmic meaning very few exceed 8
Haiti, Jan 2010 - Case study
Caused by movement on leogane fault - Caribbean and North American plate (conservative boundary)
M7.0 struck 25km SW of the capital, Port-au-Prince
Primary impacts of Haiti earthquake
250,000 deaths
1 million homeless
Most infrastructure severely damaged
Secondary impacts of Haiti earthquake
Airports and ports damaged made relief effort difficult, slow and inadequate
Looting everywhere
Lack of sanitation and clean water resulted in outbreak of disease
500,000 people still living in refugee camps 2 years later
Why were effects worse in Haiti 2010 earthquake
Shallow focus
Rarity of earthquakes
Poor building codes
