The earth’s crust is made up of 15 pieces or “plates”, which float on the molten rock below. The places where these plates meet are called faults. Along the lines of faults, the plates move and push against each other. Sometimes this causes a violent shock, with waves of tremors moving out and shaking the Earth’s surface.
The Earth’s crust consists of seven large lithospheric plates and numerous smaller plates. These plates move towards each other (a convergent boundary), apart (a divergent boundary) or past each other (a transform boundary).
Earthquakes are caused by a sudden release of stress along faults in the earth’s crust. The continuous motion of tectonic plates causes a steady build-up of pressure in the rock strata on both sides of a fault until the stress is sufficiently great that it is released in a sudden, jerky movement. The resulting waves of seismic energy propagate through the ground and over its surface, causing the shaking we perceive as earthquakes.
Induced quakes are caused by human activity, like tunnel construction, filling reservoirs and implementing geothermal or fracking projects.
Volcanic quakes are associated with active volcanism. They are generally not as powerful as tectonic quakes and often occur relatively near the surface. Consequently, they are usually only felt in the vicinity of the hypocentre.
Collapse quakes can be triggered by such phenomena as cave-ins, mostly in karst areas or close to mining facilities, as a result of subsidence.
Take a look at recent seismic activity, and you might get the impression that Earth, perhaps a bit too overcaffeinated, has a bad case of the shakes. Earthquakes rattled Chile on and off during 2010-11, beginning with a magnitude-8.8 temblor (or earthquake) that struck just off the coast near Concepcion in February 2010. Then, in March 2011, a magnitude-9.0 quake rocked Japan, triggering a tsunami that killed an estimated 29,000 people and damaged nuclear reactors. And finally, in August 2011, a magnitude-5.8 quake centered near Mineral, Va., spooked residents up and down the Atlantic seaboard and damaged the Washington Monument.
Picture Credit : Google
