Earthquakes happen rarely and when they do, they cause a lot of damage to both the geology of the area and the geography. They are the most powerful natural forces that can happen at any time. Geologists and scientists define earthquakes as vibrations of the earth's surface that occurs as a result of a release of energy in the earth's crust. The plates of the earth are constantly moving and small earthquakes can occur more often but they are not felt. When these plates slide past one another or collide into each other, large and violent earthquakes occur. These large earthquakes mostly focus on the meeting points of two plates but can also be focused on the faults that develop in the earth’s crust when the plates move. These faults can be normal meaning there is a hanging and a low bell fault, a reverse fault which is nearly horizontal or the strike slip fault which is a horizontal fault. All these can cause an earthquake but the most intense earthquake happens when blocks of the rock get locked together due to intense friction that results during movement. This builds up pressure with the continued attempt of the rocks to move thus causing an earthquake in the long run. Once the energy gets to the epicenter, the released energy spreads across the surface as rings (Richter 1958).
The main shaking created by the released energy is accompanied by foreshocks which increase the earthquake magnitude leading to the earthquake and aftershocks which decrease the earthquake strength and comes after the event. The effects of the earthquake are determined by both the energy and the state of the earth on which they occur. Strong earthquakes cause great damages. On the other hand, grounds that have previously been prone to earthquakes tend to be affected more on reoccurrence. Measurement of earthquake magnitude is done after the occurrence by use of a Richter which measures the energy released and Mercalli scale that is used to measure the intensity at the location where the earthquake occurred (Steinbrugger 1982).
The effects of earthquakes vary depending on the intensity. The strongest earthquake can cause rapture of the ground damaging dams, bridges, roads, railroad tracks and building foundations. Some cases might lead to landslide as effects of shaking. When the shaking is intense, it might lead to liquefaction of grounds built on landfill due to water mains break. Areas of landfill are prone increased shaking of earthquakes. Other damages that occur and not directly related to earthquakes include fires that result from power line fall and gas line raptures. Undersea earthquakes cause tsunamis that can travel long distances causing damage to the coastal communities (Sullivan 1982).
One major earthquake that occurred and destroyed a lot of property was the earthquake in Assam - Tibet that occurred on 15-August-1950. At least 780 people lost their lives and property was destroyed in the Nyingchi-Qamdo-Zhamo area of eastern Tibet. There were sandblows, ground cracks and large landslides in the area. Part of the Yedong village called Medog slid into the river and was washed away. This earthquake was felt at Lhasa and in Sichuan and Yunnan Provinces of China. Other areas affected by the earthquake include Sibsagar-Sadiya area of Assam, surrounding hills, Abor Hills and Subansiri River. The dam broke days after the earthquake killing 536 people. This earthquake was felt as far as Calcutta. As a result of the earthquake, there were Seiches observed in many lakes and fjords of Norway and in at least 3 reservoirs in England (Dunbar 1992).
This earthquake was measured and fount to have had a magnitude of 8.6 and has been regarded as the most important earthquake. The epicenter of this earthquake was at Rima, a region claimed by both China and Tibet. Sounds of the earthquake were heard as far as India. Measuring the epicenter, it was found to be 28.5 degrees north and 96.5 degrees east. In an attempt to study the geology of the area to understand the seismic history, it was realized that there was soil liquefaction which include sills and sand volcanoes. Studies of these deposits dated them to be 500 years back and were associated with a past seismic activity. Scientists studied the events and discovered that this earthquake was caused by two plates converging against each other (Bolt 1993).

References
Richter, C. F., (1958). Elementary seismology: San Francisco, W.H. Freeman and Company, 768 p.
Dunbar, P, K., Lockridge, P, A., and Whiteside, L,S., (1992), Catalog of significant earthquakes 2150 B.C. - 1991 A.D.: U. S. Dept. of Commerce, National Oceanic and Atmospheric Administration.
Bolt, B,A., (1993). Earthquakes: New York, W.H. Freeman and Company, 331 p.
Steinbrugge, K,V., (1982). Earthquakes, volcanoes, and tsunamis, an anatomy of hazards: 280 Park Avenue, New York, N.Y. 10017, Skandia America Group, 392 p.
Sullivan, W. (1974). Continents in Motion. New York: McGraw-Hill.