Seismic hazards Flashcards
What is an earthquake
a sudden tremor or movement of the earth’s crust, which originates naturally at or below the surface
What are P waves
They are high in frequency, short-wavelength, longitudinal waves which can pass through both solids and liquids
The ground is forced to move forwards and backwards as it is compressed and decompressed. This produces relatively small displacements of the ground
P-Waves can be refracted and reflected, and under certain circumstances can change into S-Waves
What are S-Waves
They travel more slow than P-Waves and arrive after P-waves
They are high frequency, short-wavelength waves, but are transverse
They move in all directions away from the source, at speeds which depend upon the density of the rocks through which they are moving
They cannot move through liquids
On the surface of the earth, S-Waves are responsible for the sideways displacement of walls and fences, leaving them S shaped
What are L waves
Surface waves are low frequency transverse vibrations with a long wavelength
They are created close to the epicentre and can only travel through the outer part of the crust
They are responsible for the majority of the building damage caused by earthquakes. This is because L waves have a motion similar to sea waves
The ground is made to move in a circular motion, causing it to rise and fall as visible waves move across the ground
Particles move in elliptical motions
What is the Richter scale
It is calculated from the amplitude of the largest seismic wave recorded for the earthquake, no matter what type of wave was the strongest
What is the moment magnitude scale
Scientists increasingly use this scale:
All waves are considered
Movement on the fault
Rock strength
Size of rupture
What is the Mercalli scale
Invented by Giuseppe Mercalli in 1902.
It uses the observations of the people who experienced the earthquake to estimate its intensity
