Indonesia Earthquake 8.7 Magnitude: Why There Was No Tsunami

Immediately after the 8.7 magnitude earthquake that hit off the coast of Indonesia's Aceh province, late on Wednesday evening, there was widespread fear and panic, among both the general public and the experts, of another devastating tsunami; the memories of the 2004 quake and tsunami were still fresh in many people's minds.

Tsunami warnings were issued by 28 countries in the region and disaster management and response teams from each of these governments were dispatched to critical areas in each of their lands.

Fortunately for everyone concerned, there was no tsunami.

The truth is that not all earthquakes trigger tsunamis. Wednesday's quake, for example, was a "slip-strike" quake, meaning it did not lead to the vertical displacement of giant waves. The 2004 quake, however, was a "thrust quake", meaning it did.

The difference is that in the former kind of earthquake, tectonic plates glide past each horizontally, rather than grinding over each other. However, in the latter kind, the plates push into and over each other, under the ocean, displacing huge amounts of water that then rise into mega-waves.

An Associated Press report quoted Roger Musson, a seismologist with the British Geological Survey (BGS) admitted he too feared the worst when news of the quake came through, only to be relived after learning the details.

"We have had two blocks rubbing together; it's called a strike-slip earthquake.... That means there hasn't been any displacement of the sea floor. Although an earthquake of this magnitude has the potential to cause a large tsunami, the fact that we haven't seen any drop of the sea floor, which is what generates the wave, it looks like the possibility of a tsunami being generated is low," explained another subject expert with the BGS, Susanne Sargeant, in an AFP report.

Meanwhile, in a heartening sign of how well the earthquake and tsunami warning systems instituted across the world worked, the AP report quoted the World Meterological Organisation (WMO) as saying the communications systems meant to spread information at critical times like this did their job perfectly.

"Our records indicate that all the national meteorological services in the countries at risk by this tsunami have received the warnings in under five minutes," said Maryam Golnaraghi, the Head of WMO's Disaster Risk Reduction Program.