Earthquakes Earthquakes are sudden vibrations in the Earth

Earthquakes

Earthquakes are sudden vibrations in the Earth’s crust. Whole settlements have been destroyed, sometimes with great loss of life.

Earthquakes are caused by:

Tectonic plate sliding over or past another plate along the line of fault.
Volcanic eruptions – the movement of molten rock below or on the surface.

The source of an earthquake is called focus, which is an exact location with in the Earth were waves are generated by sudden release of stored elastic energy. The epicentre is the point on the surface of the Earth directly above the focus.

Body waves: These travel through the crust:

P waves (primary) which cause the crustal to move back
S waves (secondary) we called shear waves.

Surface waves: These travel through the surface rocks:

L waves (love) which cause the surface rocks to move from slide to slide.
R waves (raleigh) which cause the surface rocks to have a vertical circular movement similar to that of water in a sea wave.

On the Richter scale is got a disengage shock a size of earthquakes.

Intensity	Characteristic	Effects Richter scale Equivalent
I.	People don’t feel any Earth movement.	<3.4
II.	A few people notice movement if at rest and/or on upper floors of tall buildings.	3.4 - 4.2
III.	Hanging objects swing back and forth. People outdoors might not realize that an earthquake is occurring.	4.2
IV.	Hanging objects swing. Dishes, windows, and doors rattle. Parked cars rock.	4.3 - 4.8
V.	Almost everyone feels movement. Sleeping people are awakened. Doors swing open/close. Dishes break.	4.9-5.4
VI.	Everyone feels movement. Objects fall from shelves. Pictures fall off walls. Furniture moves.	5.5 - 6.1
VII.	People have difficulty standing. Drivers feel cars shaking. Furniture breaks.	5.5 - 6.1
VIII.	Towers & chimneys twist and fall. Poorly built structures severely damaged. Tree branches break.	6.2 - 6.9
IX.	Well-built buildings suffer considerable damage. Some underground pipes broken. Serious damage to Reservoirs.	6.2 - 6.9
X.	Most buildings & their foundations destroyed. Some bridges destroyed. Dams damaged. Large landslides occur. Railroad tracks bent slightly.	7.0 - 7.3
XI.	Most buildings collapse. Some bridges destroyed. Underground pipelines destroyed.	7.4 - 7.9
XII.	Almost everything is destroyed. Large amounts of rock may move.	>8.0

Source: R.B. Bunnet: Physical Geography In Diagrams

Back