On Sunday 25 March 2012, slightly after 6.35 pm local time (slightly after 10.35 pm GMT), the central coast of Chile was struck by an Earthquake measured by the United States Geological Survey as 7.1 on the Richter Scale at a depth of 34.8 km, 27 km north of the city of Talca. This was felt along a stretch of coast measuring 77o km, including in the capitol, Santiago, 219 km to the north. At present only minor damage and injuries are being reported, but it is highly likely that more casualties will have occurred from a quake of this size.
Map showing the center of the quake, and the areas likely to have received the most intense shaking. USGS.
A tsunami warning was briefly issued by the Chilian Navey's Hydrographic and Oceanographic Service (SHOA), after police at Iloca and Duao reported seeing the sea withdraw sharply from the land, but this was called of shortly after, and an evacuation of low-lying coastal areas abandoned.
Chile is on the east coast of South America, where the Nazca Plate is being subducted beneath the South American Plate. As this happens the plates stick together then break apart as the pressure builds up, causing Earthquakes. This also leads to volcanic activity in the Andes Mountains, which run the length of Peru, as the Nazca Plate sinks into the Earth and is heated by the heat of the planet's interior, causing it to melt. Some of this melted material then rises through the overlying South American Plate as magma, fueling the Andean volcanoes.
Diagrammatic section through the Chile, showing how the subductive plate margin causes Earthquakes and volcanoes. Scripps Institution of Oceanography Survey of the Earthquake Zone off the Coast of Chile.
See also Eruption on Nevado del Ruiz, Columbia, Large Earthquake near Ica, Peru, New eruptions on Mount Tungurahua, Ecuador, Earthquake in Jujuy Province, NW Argentina and Earthquakes on Sciency Thoughts Youtube.