Large Earthquake off Sumatra in 2012 Heralds Tectonic Plate Breakup

Large Earthquake off Sumatra in April 2012 Heralds Tectonic Plate Breakup

Plate Breakup and the Indo-Australian Plate

The Indo-Australian Plate is breaking up -Image courtesy of Mike Norton

The tectonic plates that we see marked on a map are in a transient state. So-called ‘supercontinents’ fragment and reform over cycles of hundreds of millions of years (the Atlantic Ocean is currently still opening, and the Mediterranean basin represents the death throes of what geologists know as the Tethys Sea). In the light of this, perhaps it’s not surprising to learn that the Indo-Australian Plate is slowly – very slowly – breaking up.

The causes of this fracture are complex, and associated with the relative and conflicting directions of plate movements in the Indian Ocean. The crust is being both extended and compressed. “In the north India is meeting resistance caused by its collision with Eurasia,” says Professor Koper, “while to the south the Australian section of plate is subducting relatively smoothly beneath the Sunda plate and other associated microplates.”

Earthquake Hazards: Importance and Implications of the Research

We can usually explain earthquakes in terms of fairly straightforward movements – thrusting at subduction zones, lateral movements along transform boundaries and so on – but the unusual nature of the April 2012 Sumatran earthquake in terms of its size and location throws up questions. “We have a pretty good idea of where large earthquakes are possible, but the past several years have been humbling for seismologists,” notes Professor Koper.

Tectonic plate boundaries and epicenters of major earthquakes: Image by Keith Koper, University of Utah Seismograph Stations

“The 2004 Sumatra event was largely unexpected and the size of the recent Tohoku-oki earthquake was unexpected as well. There is a vigorous debate in the seismology community right now about whether our method of producing seismic hazard maps needs to be modified in light of these recent giant earthquakes.”

The 2012 Sumatran earthquake, then, may prove fortuitous not just in the sense that it killed so few people (USGS puts it at at least ten, compared with over almost 250,000 after the Boxing Day tsunami) but helps fuel discussion about our understanding of seismic hazard in terms of predicting the potential size of major earthquakes and the damage they might cause.