THE LAYERED STRUCTURE OF THE EARTH - Key Terms Flashcards
Stress
The force per unit area acting on or within a body
Strain
The change in shape of a body in response to stress
Seismometer
A device which receives seismic vibrations and converts them into a signal which can be transmitted and recorded
Seismogram
The paper or electronic record made by a seismograph
Seismograph
A device which receives and records seismic vibrations
Earthquake
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
Earthquake
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
Focus
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
Epicentre
The point on the Earth’s surface directly above the focus
Shadow zone
An area where earthquake waves are not recorded
Intensity
A measure of the surface damage caused by an earthquake
Mercalli
Scale that measures the intensity of an earthquake and is based on the affects that are felt in the area
Magnitude
A measure of the amount of strain energy released by an earthquake
Richter scale
A logarithmetic scale that measures the magnitude of an earthquake
Moment magnitude scale
Measures the magnitude and leverage on two sides of the fault in an earthquake
Partial melting
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.
Lithosphere
The upper rigid layer of the crust and upper mantle
Rheid
A non-molten solid that deforms by viscous or plastic flow
Low velocity zone (LVS)
Is characterised by low seismic velocities
Athenosphere
A layer of the mantle below the lithosphere
Curie Point
The temperature above which magnetic materials lose their permanent magnetism. For magnetite this is 585 degrees celcius
Remanent magnetism
Recorded in rocks due to the alignment of their magnetic minerals according to the Earth’s magnetic field at the time of their formation
Paleomagnetism
Ancient magnetism preserved in the rocks
Magnetometer
An instrument which detects the strength and direction of the magnetic field
Magnetic inclination
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
Seismic tomography
A technique for 3D imaging of the subsurface of the Earth using seismic waves
Mantle Plume
A stationary area of high heat flow in the mantle, which rises from great depths and produces magma that feeds hot space volcanoes
Apparent polar wandering curve
A line on a map which joins up the apparent positions of the magnetic north pole over time
Orogeny
A period of mountain building
Where is Moho discontinuity and its depth?
-35km
- Crust/upper mantle
What depth is the upper mantle and lower mantle boundary?
-700km
What depth and what boundary is the Gutenburg discontinuity?
-2900km
- Lower mantle/upper core
What depth and where is the Lehmann discontinuity?
-5100km
-Outer/inner core
