A2 Geohazards

Question 1

Amplitude

Answer 1

the maximum extent of an oscillation, measured from the position of rest.

Question 2

Attenuation

Answer 2

the loss of energy experienced by a wave shown as a reduction in amplitude as it propagates through a material.

Question 3

Moment

Answer 3

the turning effect of a force around a pivot.

Question 4

Liquefaction

Answer 4

describes saturated or partially saturated unconsolidated material losing strength and rigidity in response to an applied stress, usually an earthquake.

Question 5

Resonant frequency

Answer 5

the frequency at which the amplitude of the oscillation is greatest.

Question 6

Intensity

Answer 6

a measure of the surface shaking and damage caused by an earthquake. The Mercalli scale measures the intensity of an earthquake. Intensity is based on an earthquake’s local accelerations and how long these persist.

Question 7

Frequency

Answer 7

of a wave is the number of oscillations per second or the number of waves that pass through a point per second. Units are Hertz. Whilst period is the amount of time it takes for one complete oscillation or the time for one wave to pass the given point. Frequency is the inverse of the period.

Question 8

Resonance

Answer 8

the tendency to oscillate with greater amplitude at some frequencies than at others.

Question 9

Geological hazard

Answer 9

a geological condition that is dangerous or potentially dangerous to the environment and the people who live within it.

Question 10

Seismic risk

Answer 10

the possibility of suffering harm or social and environmental loss because of a seismic event that may occur in a specified period of time.

Question 11

Probability

Answer 11

a measure of the likelihood that an event will occur. Probability is quantified as a number between 0 (impossibility) and 1 (certainty).

Question 12

Return period

Answer 12

the average length of time for an earthquake of a given magnitude to occur again or to be exceeded. (Sometimes called the recurrence period.)

Question 13

Forecast

Answer 13

a statement of the probable occurrence of an event calculated from data.

Question 14

Prediction

Answer 14

a statement about what you think will happen in the future.

Question 15

Plasticity

Answer 15

the property a substance has when deformed continuously under a finite source.

Question 16

Tilt

Answer 16

calculated as the change in elevation between two points divided by the distance between those points (the first derivative of the subsidence profile). The maximum tilt occurs at the point of inflection in the subsidence trough. Tilt is usually expressed in millimetres per metre.

Question 17

Inflection point

Answer 17

a point on a curve at which the curve changes from being concave to convex, or vice versa.

Question 18

Sinkholes

Answer 18

hollows or holes in the ground caused by collapse of a surface layer, usually by dissolution of limestone.

Question 19

Talus

Answer 19

the debris accumulating at the foot of a slope due to erosion of the rock face above.

Question 20

Translational slide

Answer 20

when material begins to move as an entity, e.g. several beds sliding down slope. It usually breaks up as it gathers speed and the energy increases. Contrast the rotational slide that marks failure of incompetent, clay-rich rocks.

Question 21

Isotropic clay

Answer 21

having equal properties in all directions. This is not the same as being homogeneous, which conveys being made of the same material throughout. A slate can be homogeneous in being made of metamorphosed mudstone but is not isotropic in that it has a strong cleavage.

Question 22

Tsunamite

Answer 22

a tsunami deposit which is a sedimentary unit deposited onshore during the inundation phase. The offshore deposits as the water retreats are different.