3.a. There is a variety of earthquake activity and resultants landforms and landscapes Flashcards
What is an earthquake?
A release of stress that has built up within the Earth’s crust caused by tension, compression, and shearing of rocks.
A series of seismic shock waves originate from what? What is this?
The earthquake focus.
An earthquake focus is the term used to describe the location where the stress is suddenly released.
What is the earthquake epicentre?
The point immediately above the earthquake focus, at the Earth’s surface.
What are some earthquake events preceded by? What do these indicate?
Preceded by several fore-shocks, often indicating a large event is likely.
This can give some populations several hours warning.
What often happens after an earthquake event?
A series of after-shocks follow the main quake, gradually reducing in intensity.
Which produce greater impacts, volcanoes or earthquakes?
The impacts of earthquakes significantly out-weigh the impacts of volcanoes.
Earthquake activity tends to be concentrated in one of four locations. What are they?
Ocean trenches and island arcs (convergent).
Transform plate margins.
Collision zones (convergent).
Mid-ocean ridges (divergent).
Which is the one of the four earthquake locations produces the strongest events? Why?
Ocean trenches and island arcs (convergent).
This is because there are compressive forces associated with the subduction of one plate below another.
Which is the one of the four earthquake locations produces the second strongest events? Why?
Transform plate margins.
This is because there are shearing forces associated with the intermittent movement of one plate past another.
Which is the one of the four earthquake locations produces the second weakest events? Why?
Collision zones (convergent).
This is because it features compressive forces associated with the grinding together of plates carrying continental crust.
Which is the one of the four earthquake locations produces the weakest events? Why?
Mid-ocean ridges (divergent).
This is because there are tensional forces associated with spreading processes and subsequent faulting and rifting.
What are seismic waves?
Waves that can travel both along the surface and through the layers of the Earth.
There are three types of seismic wave.
Outline primary (P) waves.
Fast-travelling.
Low-frequency compressional waves.
They vibrate in the direction in which they travel.
Travel through solids and liquids.
Outline secondary (S) waves.
Half the speed of P waves.
High-frequency waves.
They vibrate at right angles to the direction in which they travel.
Can only travel through solid material.
More powerful than S waves.
Outline surface (L) waves.
Slowest of the three types.
Low-frequency waves.
Some L waves have a rolling movement that moves the surface vertically, while other move the ground at right angles to the direction of movement.
How are earthquakes often categorised?
Categorised according to their depth of focus.
Outline shallow focus earthquakes.
Surface down to about 70 km.
Shallow quakes occur in cold, brittle rocks resulting from the fracturing of rock due to stress within the crust.
They are very common, with many releasing only low levels of energy, although other high-energy shallow quakes are capable of causing severe impacts.
What is triangulation?
The process by which multiple seismometers are used to locate an earthquake event.
Deep focus earthquakes occur in what range?
70 km - 700 km.
As you get closer to the core, what happens? What may happen to minerals? How does this relate to deep focus earthquakes?
Increasing depth, pressure - with temperatures increasing to very high levels.
Minerals change type and volume, which may contribute to a release of energy.
It is likely that dehydration of water in subducting plates plays a significant role in these events but scientists continue to evolve their ideas about these less frequent but often powerful quakes.
What does the Richter scale assess?
(The Richter Scale)
(Different measures of assessing earthquake magnitude)
Earthquake energy.
When was the Richter scale developed? How does it measure magnitude?
(The Richter Scale)
(Different measures of assessing earthquake magnitude)
1935, uses amplitude of seismic waves to determine earthquake magnitude.
What type of scale is the Richter scale? What is this?
(The Richter Scale)
(Different measures of assessing earthquake magnitude)
A logarithmic scale, so each whole-number increase in magnitude represents a ten-fold increase in the amplitude of the seismic wave.
Each whole-number increase also represents a 30-fold increase in the release of energy.
What is the upper limit of the Richter scale? What are the most powerful events seen?
(The Richter Scale)
(Different measures of assessing earthquake magnitude)
Has no upper limit, although the most powerful earthquakes record a magnitude of around 9 (e.g. Tohoku, Japan in 2011).
