2.9 Seismic tomography and Mantle plumes Flashcards

1
Q

What technique can be used to identify differences in density within the mantle?

A

seismic tomography

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2
Q

What is seismic tomography?

A

a technique in which a virtual 3D model is built up by analysing the behaviour of seismic waves as they pass through sections of a body

it involves looking for variations in P wave velocities

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3
Q

How does seismic tomography work?

A

variations in P wave velocity are recorded by analysing anomalies where earthquake waves do not arrive at the seismograph at the expected times

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4
Q

What is the significance of P waves that are faster than average for the Earth?

A

waves travel faster in colder rocks

colder rocks are more rigid

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5
Q

Why is the seismic velocity higher than expected under mountain ranges?

A

this observation supports the theory of isostasy which suggests that mountains have cold ‘roots’ which extend into the mantle

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6
Q

Why is the seismic velocity higher than expected near ocean trenches?

A

seismic anomalies indicate the presence of cold rock - the subducting plate

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7
Q

What is the generally accepted explanation of negative (slower) anomalies in seismic velocity in the mantle?

A

mantle plumes
these anomalies extend to the core-mantle boundary and are associated with surface hotspots

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8
Q

What is a hotspot?

A

an area of high heat flow and volcanic activity at the surface associated with mantle plumes

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9
Q

What is a mantle plume?

A

a stationary area of high heat flow in the mantle, which rises from great depths and produces magma that feeds hot spot volcanoes

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9
Q

What is a mantle plume?

A

a stationary area of high heat flow in the mantle, which rises from great depths and produces magma that feeds hot spot volcanoes

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