Earthquakes are sudden, rapid vibrations of the earth caused by sudden rupturing and shifting of rock beneath the earth surface.
The vibration of earth can range from barely noticeable to extremely destructive.
Earthquake vibrations occur in a variety of frequencies and velocities. The actual rupture process may last from a few seconds to as long as one minute for a major earthquake.
Classes of earthquake:
There are three classes of earthquake that are known & recognized as, tectonic, volcanic and artificially produced
- Tectonic: Tectonic quake are by far the most common, devastating and most difficult to predict. They are caused by stresses set up by movements of a dozen or so huge plates that form the earth’s crusts. Most earthquakes occur at the boundaries of these plates. Where two plates slides over and collides against each other; some earthquakes do occur in the middle of plates.
- Volcanic: Volcanic quakes are seldom very large or destructive; they often precede or accompany volcanic eruption.
- Artificial: Artificially produced earthquake are induced by activities such as the filling of new reservoir or the pumping of fluid deep into the earth through wells. This type of earthquake can be noticeable but are hardly destructive.
Affects of earthquake
Earthquakes are one of the most destructive of natural hazards. They may occur at any time of year, day or night, with sudden impact and little warning. Destroy buildings and or damage structure of the building, bridges, and communications -
- Loss of human lives
- Dense casualties/injuries
- Extensive property damages
- Disruption/Disturbance to normal human life activities
- Destabilize the government, economy and social structure of a country.
Secondary Hazards
When earthquake occur, a variety of secondary and related hazards can happen simultaneously. The ground shaking from earthquakes can cause landslides, rock fall, debris flow, soil liquefaction, avalanches, tsunami, fire etc.
Factors contributing the vulnerability
Several key factors contribute to vulnerability of human populations:
- Location of settlements in seismic areas, especially on poorly consolidated soils, on ground prone to landslides or along fault lines.
- Building structures, such as homes, bridges, dams, which are not resistant to ground motion.
- Dense groupings of buildings with high occupancy.
- Lack of access to information about earthquake risks.
Earthquake Fault line
An earthquake fault is a zone within the earth’s crust where the rocks have been weakened by previous earthquake, and where we expect earthquake slip to occur.
Where earthquakes most often occur?
The earth’s surface is broken into a dozen or so major plates, plus a number of smaller plates and those plates are moving with respect to each other. The motion between two major tectonic plates is the main causes of occurring of earthquakes.
Whether earthquakes are predicted?
The seismological research has indicated the seismic zones and geologic fault and has warned that where earthquakes are going to occur, but difficulty is that it cannot be predict when it will occur.
Foreshock and after shock
Foreshocks are small scale earthquakes that occur before a large earthquake. Aftershocks may occur hours, days, weeks, or even months following the large quake.
