Plenty of Activity But No Large Earthquakes: 25-31 December 2012

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Mid-Ocean Ridge Earthquakes

Transform faults are the source of many mid-ocean ridge earthquakes. Image credit: USGS

Mid-ocean ridge earthquakes are generally smaller than those at collision or subduction zones, so the presence on the map of a number of tremors in ocean-ridge settings actually implies a higher level of activity than usual.

The last week of 2012 saw earthquakes of M5.0-M5.5 in the south Atlantic, south Pacific and southern Indian oceans.

In contrast to the Himalayas where plates are moving together, mid-ocean ridges are where tectonic plates move apart and new earthquakes are generated. Ridges are not continuous but are offset, and fracture zones lie between the segments: These are the usual sources of such earthquakes.

One earthquake worth particular note is the M5.0 which occurred south of India along the Ninety-East Ridge. Although not marked on maps as a plate boundary, some seismologists believe that this area may mark the beginnings of a new plate boundary between the Indian and Australian plates.

Predicting Earthquakes

In his book The Million Death Quake, seismologist Roger Musson argues that only the broadest predictions can be made about when and where an earthquake will occur. To demonstrate just how general, he makes a prediction of his own. “Magnitude greater than 6, Pacific region, next week. It’s likely to happen whichever week you pick.” The fact that it didn’t happen this week not only proves his point about the fallibility of earthquake prediction – it also shows what a slow week, in seismological terms, this has been.

Sources

Musson, R. The Million Death Quake. (2012). Macmillan.

United States Geological Survey. Real time earthquake map. (2012). Accessed December 31, 2012.

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