Earth's Structure

Question 1

Earthquake

Answer 1

Vibration in rocks of the crust and upper mantle caused by a sudden dislocation along a fault

Question 2

The Elastic Rebound Theory

Answer 2

• two parts of rock are under stress due to opposing forces due to tectonic plates
• it deforms as its put under strain and creates elastic strain energy
• deformation continues until stress overcomes strength and it fractures

Question 3

P waves

Answer 3

• travel fast and arrive first
• longitudinal, back and forth
• move together in the direction of the wave

Question 4

S waves

Answer 4

• arrive after P waves
• move at right angles to the wave
• larger in amplitude than P waves

Question 5

L waves

Answer 5

• surface wave, lose energy fast
• longer wavelength
• slowest of waves

Question 6

Focus

Answer 6

Where the earthquake originates

Question 7

Epicentre

Answer 7

The point above the earthquake on the earth’s surface

Question 8

Shadow Zone

Answer 8

• waves are refracted at the guttenburg discontinuity between 103 and 142
• s waves aren’t received beyond 142, p waves arrive late

Question 9

Partial Melting

Answer 9

Rock melts, liquid fraction surrounds the crystals which are solid reducing it’s rigidity so it’s like a rheid

Question 10

Oceanic crust compostion

Answer 10

Fe and Mg
Basalt Pillow lavas
Dolerite dykes
Gabbro in layers

Question 11

Oceanic crust properties

Answer 11

2.9g/cm3 density
200Ma oldest crust
7km average thickness

Question 12

Continental crust composition

Answer 12

Al and Si
Granitic, igneous, sedimentary and metamorphic rocks

Question 13

Continental crust properties

Answer 13

2.7g/cm3 density
4000Ma oldest crust
35km average thickness

Question 14

Ophiolite

Answer 14

Section of the oceanic crust and upper mantle broken off and attached to the edge of the continent during plate movement

Question 15

Xenolith

Answer 15

Fragment of foreign rock in igneous rock

Question 16

Peridotite

Answer 16

Ultramafic igneous rock composed of olivine and pyroxene

Question 17

Subduction in relation to the earth’s structure

Answer 17

High velocity zones indicating the presence of cold rock beneath the coastline
Cold lithospheric plates have descended into the mantle

Question 18

Curie point

Answer 18

Temperature in which magnetic materials lose their magnetism

Question 19

What causes paleomagnetism?

Answer 19

• ‘frozen compasses’
• iron materials in lavas align themselves with the earth’s magnetic field to retain paleomagnetism permenantly

Question 20

What is isostasy?

Answer 20

• strong negative gravity anomalies across mountain ranges
• less dense continental crust sinks down into the mantle until in a state of balance
• supported by rocks in the mantle

Question 21

Why is the interior of the earth hot?

Answer 21

• volcanoes erupt molten lava
• temperature increases with depth, highest temp is at the core
• mantle stores a great amount of heat as silicates are poor conductors of heat
• known as the geothermal gradient

Question 22

Radioactive decay

Answer 22

• unstable parent atoms change to stable daughter atoms transferring thermal energy to the earth

Question 23

Advection

Answer 23

• thermal energy is transferred through a medium as a fluid
• sea water is drawn down into the crust and replaces hydrothermal fluids

Question 24

Conduction

Answer 24

• thermal energy transferred through a substance with no overall movement

Question 25

Convection

Answer 25

• thermal energy is transferred by a substance due to buoyancy differences in the substance
• hot material expands, density reduces ans materials rise then sinks when colder

Question 26

Characteristics of MOR

Answer 26

• high heat flows
• rising magma
• eruptions

Question 27

Characteristics of subduction zones

Answer 27

• deep ocean trenches
• low head flow
• evidence of compression