The quake was reported along the Sunda Megathrust or Great Sumatran Fault, a fault line off Sumatra's western coast that separates the Sunda Plate from the Australian Plate. The location was 191 kilometers southwest of the city of Sungai Penuh, near the Mentawai Islands in the Indian Ocean, at a depth of 40 kilometers.
The same fault line also produced the catastrophic Boxing Day earthquake and tsunami in 2004 that killed a quarter-million people. Authorities have not issued a tsunami warning in response to the Tuesday quake.
Sitting at the convergence of several tectonic plates, Indonesia is home to numerous volcanoes and often subjected to earthquakes both sundry and powerful. A day earlier, a quake of similar strength was reported hundreds of miles to the east, off the southern coast of the island of Papua New Guinea.