THE LAYERED STRUCTURE OF THE EARTH - Key Terms

Question 1

Stress

Answer 1

The force per unit area acting on or within a body

Question 2

Strain

Answer 2

The change in shape of a body in response to stress

Question 3

Seismometer

Answer 3

A device which receives seismic vibrations and converts them into a signal which can be transmitted and recorded

Question 4

Seismogram

Answer 4

The paper or electronic record made by a seismograph

Question 5

Seismograph

Answer 5

A device which receives and records seismic vibrations

Question 6

Earthquake

Answer 6

A vibration in the rocks of the crust and upper mantle caused by a sudden dislocation of the rocks along a fault, but sometimes from an explosion such as a nuclear bomb

Question 7

Earthquake

Answer 7

A vibration in the rocks of the crust and upper mantle caused by a sudden dislocation of the rocks along a fault, but sometimes from an explosion such as a nuclear bomb

Question 8

Focus

Answer 8

The point within the Earth at which the earthquake originates as movement occurs along a fault plane. Seismic waves radiate from the epicentre in all directions

Question 9

Epicentre

Answer 9

The point on the Earth’s surface directly above the focus

Question 10

Shadow zone

Answer 10

An area where earthquake waves are not recorded

Question 11

Intensity

Answer 11

A measure of the surface damage caused by an earthquake

Question 12

Mercalli

Answer 12

Scale that measures the intensity of an earthquake and is based on the affects that are felt in the area

Question 13

Magnitude

Answer 13

A measure of the amount of strain energy released by an earthquake

Question 14

Richter scale

Answer 14

A logarithmetic scale that measures the magnitude of an earthquake

Question 15

Moment magnitude scale

Answer 15

Measures the magnitude and leverage on two sides of the fault in an earthquake

Question 16

Partial melting

Answer 16

Occurs when a small proportion (usually between 1% and 5%) of a rock melts. The liquid fraction surrounds crystals which are still solid. This reduces the rigidity of the rock and allows it to behave as a rheid.

Question 17

Lithosphere

Answer 17

The upper rigid layer of the crust and upper mantle

Question 18

Rheid

Answer 18

A non-molten solid that deforms by viscous or plastic flow

Question 19

Low velocity zone (LVS)

Answer 19

Is characterised by low seismic velocities

Question 20

Athenosphere

Answer 20

A layer of the mantle below the lithosphere

Question 21

Curie Point

Answer 21

The temperature above which magnetic materials lose their permanent magnetism. For magnetite this is 585 degrees celcius

Question 22

Remanent magnetism

Answer 22

Recorded in rocks due to the alignment of their magnetic minerals according to the Earth’s magnetic field at the time of their formation

Question 23

Paleomagnetism

Answer 23

Ancient magnetism preserved in the rocks

Question 24

Magnetometer

Answer 24

An instrument which detects the strength and direction of the magnetic field

Question 25

Magnetic inclination

Answer 25

The angle of dip of the lines of a magnetic field. It is the dip angle made with the horizontal and the Earth’s magnetic field lines, measured with a compass

Question 26

Seismic tomography

Answer 26

A technique for 3D imaging of the subsurface of the Earth using seismic waves

Question 27

Mantle Plume

Answer 27

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

Question 28

Apparent polar wandering curve

Answer 28

A line on a map which joins up the apparent positions of the magnetic north pole over time

Question 29

Orogeny

Answer 29

A period of mountain building

Question 30

Where is Moho discontinuity and its depth?

Answer 30

-35km
- Crust/upper mantle

Question 31

What depth is the upper mantle and lower mantle boundary?

Answer 31

-700km

Question 32

What depth and what boundary is the Gutenburg discontinuity?

Answer 32

-2900km
- Lower mantle/upper core

Question 33

What depth and where is the Lehmann discontinuity?

Answer 33

-5100km
-Outer/inner core