Earthquake of 8.7 Magnitude that hit Aceh Province of Indonesia sparked Tsunami Alert

Powerful earthquake of 8.7 magnitude on the Richter scale hit Aceh province of Indonesia on 11 April 2012. The quake sparked a short-lived tsunami alert for much of the Indian Ocean. The earthquake's epicentre was at a depth of 33 km about 485 km from Indonesia's Banda Aceh, a region regularly hit by earthquakes.

The U.S. Geological Survey stated that the first earthquake had a magnitude of 8.6 and was quickly followed by an 8.2-magnitude aftershock.

There was a tsunami, but the waves were just below 1 meter [3.3 feet] as against the December 2004 tsunami, when waves reached heights of nearly ten stories.

Two main reasons as to why the earthquake off Indonesia did not spawn a giant tsunami were highlighted

•    The quake was of a smaller magnitude—8.6, contrasted with 9.3 for the temblor that struck off the west coast of Sumatra, Indonesia, in 2004.
•    Second, the quake was a strike-slip earthquake, where the motion is primarily side-to-side unlike the 2004 quake when vast swaths of the seafloor thrust sharply upward, drastically disturbing the waters above.

Also experts found it strange that the quake on 11 April 2012 did not occur at a so-called subduction zone, where tectonic plates collide and one dives beneath the other into Earth's mantle. The earthquake happened about a hundred miles (150 kilometers) from the nearest subduction zone, making the temblor an intraplate quake. Intraplate quakes tend to be much smaller.

The temblors caused several countries in the region to issue tsunami watches. The alarm was however lifted after a few hours when no serious waves were observed. In India, the earthquake was also felt in Kolkata, Chennai, Bangalore and several other cities on the Indian eastern coast.

Earlier the Indian Ocean tsunami of 2004 had killed 170000 people in Aceh. Indonesia had launched a $130-million tsunami warning system in November 2008 in a bid to prevent a repeat of tragedies like the 2004 disaster.