Yesterday’s M8.6 earthquake was a very unusual strike-slip earthquake - EQECAT

The shallow M8.6 earthquake that occurred 400km offshore northern Sumatra, Indonesia on 11 April 2012 did not cause any major damage, despite tsunami warnings being issued following the main quake and a M8.2 aftershock.

The aftershock affected wave heights by up to one metre but did not cause a tsunami of consequence, mainly due to its strike-slip mechanism, according to EQECAT.

The earthquake caused little to no damage or injuries despite being felt at distances of 1,000km or more, from Thailand to Sri Lanka and from Jakarta to Kolkata. Shaking felt onshore was of low to moderate intensity.

This is the fifth earthquake of magnitude 8.6 or larger to have occurred since 2004, prior to which 40 years passed without a single worldwide occurrence of a M8.6 or larger earthquake.

However, the latest quake is of great seismological interest, says EQECAT. The earthquake, whose epicentre was located about 100km southwest of the Sunda-Sumatra trench, was not associated with the plate boundary megathrust fault.

A crustal, strike-slip earthquake of this magnitude is very unusual and indicates a previously unknown fault of considerable length at this location. The cat modelling firm anticipates that research resulting from the quake will determine if its rupture characteristics have implications regarding conventional thought on strike-slip faults worldwide.