Tectonics EQ1 Flashcards
(13 cards)
Where do most earthquakes occur?
At plate boundaries
What type of plate boundaries usually lead to the most powerful earthquakes?
Convergent & Conservative
What percentage of earthquakes occur at plate boundaries?
95%
Where are active volcanoes most usually found?
At or near plate boundaries, in particular the Ring of Fire (75%)
What percentage of all earthquakes are found in the Ring of Fire?
70%
Why can intra-plate earthquakes occur?
Usually due to hotspots or old fault lines
What did Alfred Wegener propose?
The theory of continental drift where the continents were once joined together but have gradually moved over time
What are some evidence of continental movement?
Basalt lava flows where continents tear apart
Coal in Antarctica
Fossils of Mesosaurus
Fossils of Glossopteris
Outlines of continents piece together
What is the plate tectonic theory?
The Earth consists of plates which have a section of lithosphere, that move slowly over the lower mantle due to convection- this leads to crust being created, destroyed, torn or thrust up
Is the oceanic crust or the continental crust thicker?
Continental. (70km), whilst oceanic is 6km thick
Is the ocean crust or the continental crust more dense?
Oceanic. Continental crust has 60% silica content, making it less dense than oceanic which has basic composition (similar to basaltic lava)
What is the Mohorovicic Discontinuoty?
The division between the upper mantle and lower mantle, due to differences in seismic wave speed
What is the Benioff Zone?
