(CBC)

An 8.6-magnitude earthquake hit waters off Banda Aceh, Indonesia, on April 11, putting the region from Thailand to India on alert for the possibility of a tsunami.

The U.S. Geological Survey reported that the quake was centred 33 kilometres beneath the ocean floor around 495 kilometres from Banda Aceh.

Indonesia is on the western edge of the so-called Pacific Ring of Fire, a 40,000-kilometre area that hosts 452 volcanoes and is home to constant earthquake and volcanic activity.

Just over a year ago, a severe earthquake in Japan registering magnitude 8.9 led to a tsunami that ended up killing more than 15,000 people and causing hundreds of billions of dollars in damage.

The Ring of Fire is a horseshoe-shaped area that extends around much of the perimeter of the Pacific Ocean from New Zealand north to Papua New Guinea, west to Indonesia, north through Japan, across the Bering Sea to Alaska, down the west coast of North America, through Central America and along the coast of Peru to Chile.

Tectonic activity

The surface of our planet is comprised of a series of large tectonic plates. Approximately 80 kilometres deep, they hover on top of Earth’s hot, malleable centre.

At the base of oceans, the crust is created by small eruptions of hot lava that are immediately cooled by frigid deep-sea water. To accommodate the constant addition of new ocean crust, the Earth’s plates move, creating the potential for intense geological activity at the edges and on the surface.

When adjoining plates slide past one another, the movement can have one of three outcomes:

• If the plates move towards each other, one ends up becoming submerged beneath the other, thus leading to an earthquake.
• If the plates move away from each other, they create space for new ocean floor.
• Or, the two boundaries could just slide past each other without incident.

The Pacific Ring of Fire is made up of a series of oceanic trenches and volcanic arcs and contains a number of abutting plates.

Earthquake activity in New Zealand and Indonesia, for example, is the result of friction between the Australian plate and the Pacific plate; the notorious San Andreas fault, which runs a 1,300-kilometre course through California, is the boundary between the Pacific plate and the North American plate.

The most volatile Canadian stretch of the Ring of Fire is likely the Queen Charlotte fault just north of the Haida Gwaii archipelago off the B.C. coast.

It has produced a number of significant earthquakes since 1929, and has the distinction of generating Canada’s largest recorded earthquake – a magnitude 8.1 that struck in 1949.