Earthquakes occur when two blocks of the earth suddenly slip past one another (Wald, N.D.). Magnitude 2 or below happen hundreds of times a day throughout the world. While major quakes (Magnitude 7 or above) happen approximately once a month.
Residents of the South Pacific Papua New Guinea woke up to a 7.5 quake. No reports of injuries were reported.
The M 7.5 April 19, 2014 earthquake southwest of Panguna, Papua New Guinea, occurred as the result of thrust faulting on or near the subduction zone interface between the subducting Australia plate and overriding Pacific plate. At the location of the earthquake, the Australia plate moves towards the east-northeast at a velocity of 102 mm/yr with respect to the Pacific, and begins its subduction into the mantle beneath Bougainville Island at the New Britain Trench south of the earthquake.
References
Wald, L. (N.D.). What is an earthquake? Retrieved April 19, 2014, from http://earthquake.usgs.gov/learn/kids/eqscience.php