A2 Geohazards Flashcards
Amplitude
the maximum extent of an oscillation, measured from the position of rest.
Attenuation
the loss of energy experienced by a wave shown as a reduction in amplitude as it propagates through a material.
Moment
the turning effect of a force around a pivot.
Liquefaction
describes saturated or partially saturated unconsolidated material losing strength and rigidity in response to an applied stress, usually an earthquake.
Resonant frequency
the frequency at which the amplitude of the oscillation is greatest.
Intensity
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.
Frequency
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.
Resonance
the tendency to oscillate with greater amplitude at some frequencies than at others.
Geological hazard
a geological condition that is dangerous or potentially dangerous to the environment and the people who live within it.
Seismic risk
the possibility of suffering harm or social and environmental loss because of a seismic event that may occur in a specified period of time.
Probability
a measure of the likelihood that an event will occur. Probability is quantified as a number between 0 (impossibility) and 1 (certainty).
Return period
the average length of time for an earthquake of a given magnitude to occur again or to be exceeded. (Sometimes called the recurrence period.)
Forecast
a statement of the probable occurrence of an event calculated from data.
Prediction
a statement about what you think will happen in the future.
Plasticity
the property a substance has when deformed continuously under a finite source.
Tilt
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.
Inflection point
a point on a curve at which the curve changes from being concave to convex, or vice versa.
Sinkholes
hollows or holes in the ground caused by collapse of a surface layer, usually by dissolution of limestone.
Talus
the debris accumulating at the foot of a slope due to erosion of the rock face above.
Translational slide
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.
Isotropic clay
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.
Tsunamite
a tsunami deposit which is a sedimentary unit deposited onshore during the inundation phase. The offshore deposits as the water retreats are different.
