2012: Major Earthquakes but Relatively Few Deaths

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Earthquakes in 2012. Image credit: USGS

Earthquakes in 2012. Image credit: USGS

The last week of 2012 was a relatively quiet one, seismologically speaking at least.

But how did the rest of the year shape up in terms of earthquake activity?

There’s no detailed catalogue available of every earthquake on the planet, but the United States Geological Survey produces some summary lists… although these come with the caveat that they are not complete.

How Many Large Earthquakes Were There in 2012?

The USGS’s selective statistics show all earthquakes of magnitude 7 or more (≥M7.0) for the year, and a separate listing includes ‘significant’ tremors of ≥M6.5 or tremors which caused major damage.

This second list, which at the time of writing had been updated only as far as mid-November, is incomplete but still includes more than 60 seismic events, while in the first listing shows 16 significant earthquakes.

How does this compare to what is expected? Well, although the USGS publishes estimates for a typical year by magnitude category (M4.0-4.5, for example) this doesn’t match up exactly to the available earthquake information for 2012. What we can say, however, is that the recorded number of earthquakes ≥M7.0 for 2012 is pretty consistent with the ‘typical’ year – 16 recorded compared to 15 ‘expected’.

2012’s Largest Earthquakes

There’s no question what the major seismic event of 2012 was and it’s perhaps surprising that two earthquakes of M8.6 and M8.2, occurring within two hours close together off the west coast of northern Sumatra on the 11 April, didn’t attract more attention, especially given that this notoriously active seismic zone was the broad source region for the Boxing Day earthquake of 2004.

Despite their scale and associations, the two earthquakes (or mainshock and aftershock) passed unremarked largely because they caused so little damage. They were located within the Indian plate rather than at the plate boundary; the nature of the faulting was lateral, rather than vertical; and although a tsunami was generated it was small, localised and caused no damage. USGS reported just 2 deaths as a result of the tremors and a further 8 from heart attacks.

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