What is an earthquake?
Movements within the Earth’s crust cause stress to build up at points of weakness and rocks to deform.
Stored energy builds up in the same way as energy builds up in the spring of a watch when it is wound.
When the stress finally exceeds the strength of the rock, the rock fractures along a fault, often at a zone of existing weakness within the rock. The stored energy that is suddenly released as an earthquake!
Intense vibrations, or seismic waves, spread out from the initial point of rupture, the focus, like ripples on a pond. These waves are what makes the ground shake and can travel large distances in all directions.
Near the focus, the waves can be very large, making them extremely destructive
Causes of Earthquake
Earthquakes are caused by sudden tectonic movements in the Earth’s crust. The main cause is that when tectonic plates, one rides over the other, causing orogeny collide (mountain building), earthquakes.
The largest fault surfaces on Earth are formed due to boundaries between moving plates.
The stress increases when they stick, relative motion between the plates. This continues until the stress rises and breaks, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy as shock waves.
Such faults are San Andreas fault in San Francisco, Rift valley in Africa etc.
Effects of Earthquake
The effects of an earthquake are terrible and devastating. Many building, hospitals, schools, etc are destroyed due to it. A lot of people get killed and injured.
Many people lose their money and property. It affects the mental health and emotional health of people.
The environmental effects of it are that including surface faulting, tectonic uplift and subsidence, tsunamis, soil liquefaction, ground resonance, landslides and ground failure, either directly linked to a quake source or provoked by the ground shaking.
Seismic magnitude scales
Seismic magnitude scales are used to describe the overall strength or “size” of an earthquake. These are distinguished from seismic intensity scales that categorize the intensity or severity of ground shaking (quaking) caused by an earthquake at a given location.
Magnitudes are usually determined from measurements of an earthquake’s seismic waves as recorded on a seismogram. Magnitude scales vary on what aspect of the seismic waves are measured and how they are measured.
Different magnitude scales are necessary because of differences in earthquakes, the information available, and the purposes for which the magnitudes are used.