Indonesia:Padang Earthquake (September 30, 2009) Explained

Padang Earthquake (September 30, 2009) and Banda Aceh quake (December 26, 2004) Explained

Indonesia lies on the Pacific Ring of Fire. Consequently it is an area great crustal instability. Today's earthquake of magnitude 7.6 struck at sea at 10:16 UTC at a depth of 87 kilometres (54 miles), 53 kilometres northwest of Padang city in West Sumatra province, the United States Geological Survey reported. This was followed by another quake of magnitude 5.5 at 10:38 UTC.
The great Indo-Australian Plate (Indian Plate) underlies the Indian Ocean and Bay of Bengal and is drifting north-east at an average of 6 cm/year (2 inches per year). The Indo-Australian Plate (Indian Plate) subducts the Burma Plate (Eurasian Plate) at the Sunda Trench. Padang city lies close to this subduction zone. A megathrust fault is the boundary between a subducting and an overriding plate. A megathrust earthquake is produced by a sudden slip along this fault.

The town of Padang has been devastated. At the time of writing 75 people are reported dead with thousands of people trapped under collapsed buildings.

The 2004 Indian Ocean earthquake was an undersea megathrust earthquake that occurred with an epicentre off the west coast of Sumatra (off Banda Aceh). The 9.15 magnitude quake, had its epicentre roughly 600km northwest of Padang.
c 1,600 km (994 mi) of faultline slipped (or ruptured) about 15 m (50 ft) along the subduction zone where the India Plate slides (or subducts) under the overriding Burma Plate (Eurasian Plate). The earthquake triggered a series of devastating tsunami along the coasts of most landmasses bordering the Indian Ocean, killing nearly 230,000 people in eleven countries, and inundating coastal communities with waves up to 30 meters (100 feet) high. Coastal locations in Indonesia, Sri Lanka, India, and Thailand suffered most.

Italy: Video of Earthquake scene in Central Italy around L'Aquila in the Apennines (6/4/09)

More than 100 people are believed dead and as many as 50,000 are left homeless after an earthquake hit L'Aquila and other towns in central Italy. About 1,500 people were injured and many people are still missing as rescuers search desperately for survivors trapped beneath rubble. The 6.3-magnitude quake struck at 0330 (0130 GMT) close to L'Aquila

Tectonic Summary

The April 6th 2009 earthquake in Central Italy occurred as a result of normal faulting on a NW-SE oriented structure in the central Apennines, a mountain belt that runs from the Gulf of Taranto in the south to the southern edge of the Po basin in northern Italy. Geologically, the Apennines are largely an accretionary wedge formed as a consequence of subduction. This region is tectonically and geologically complex, involving both subduction of the Adria micro-plate beneath the Apennines from east to west, continental collision between the Eurasia and Africa plates building the Alpine mountain belt further to the north and the opening of the Tyrrhenian basin to the west. The evolution of this system has caused the expression of all different tectonic styles acting at the same time in a broad region surrounding Italy and the central Mediterranean. The April 6th, 2009 earthquake is related to normal faulting and the east-west extensional tectonics that dominate along the entire Apennine belt, primarily a response to the Tyrrhenian basin opening faster than the compression between the Eurasian and African plates.(USGS)