As 2015 closes in on a dynamic Earth, and bearing in mind that there were no outstanding seismic events in the week, it’s a good time to swap the weekly digest for a yearly one and take a quick look back over the events of 2014.
How was it?
Although some weeks, it may have felt as though the whole planet was rocking – and others were deeply and suspiciously still – overall the year’s earthquakes came in… well, pretty near average.
The United States Geological Survey gives (broad) annual average figures of 1 earthquake of at least magnitude 8 (≥M8.0); 15 of M7.0-M7.9; and 134 of M6.0-M6.9. 2014 (barring anything in the next few hours, of course) mustered 1 ≥M8.0; 11 of M7.0-M7.9; and 135 of M6.0-M6.9.
The Year’s Largest Earthquake: M8.2, Chile
April 2 saw the largest earthquake of the year — an M8.2 off the coast of Chile which generated a tsunami of around seven feet in height and killed six people, though it also caused considerable damage along the coastal area.
Tectonically speaking the event wasn’t unexpected; subduction margins such as that along the western coast of South America (where the Nazca plate descends below the South American continent) are characterised by large tremors, and the largest seismic events on record have occurred there.
The April 2014 event was interesting because it occurred in a part of the margin which hadn’t experienced a major earthquake for a long period of time — a so-called seismic gap. The USGS notes, however, that two tremors even larger than that of 2014 — both estimated at around M8.8 — occurred in the latter half of the nineteenth century.
M6.9, China: February 2014
February’s M6.9 tremor in central China was in no sense one of the largest in the world in 2014 but it did occur in an area where, historically, the death tolls from even moderately-sized earthquakes can be significant as a result of dense population in high energy environments.
Tectonically, southern-central China is affected by the collision of India and Asia. Because both are made of relatively buoyant continental crust, the result of the collision is uplift rather than subduction and the crust is lifted and faulted over very many thousands of square kilometres — in this case forming the Himalayas and the Tibetan plateau.
Such uplift produces complex faulting throughout the uplifted area, and earthquakes are common. No deaths were reported as a result of the 2014 earthquake — a remarkable fact considering that around 600 were reported killed in a smaller tremor in the same region in August and that the USGS lists of the most deadly tremors includes four in China (and others in the broader Indo-Eurasian collision zone) which killed tens of thousands. Most recently, a tremor killed over 85,000 people in 2008.
US Quakes: Where Else But Oklahoma?
They weren’t the biggest in the US (easily outstripped by an M7.9 in the Aleutian Islands and an M6.8 off Ferndale) but we can’t let 2014 pass without mentioning Oklahoma’s earthquakes. The swarm of small to medium tremors in the state, extending at times into Kansas and Texas, is significant because scientific evidence suggests that this area (admittedly known beforehand as ‘earthquake country’) is experiencing increased seismicity as a result of human activity.
2014: An Interesting Year, Seismically Speaking
In many ways, 2014 was a good year, with no seriously devastating tremors such as those which scarred 2011 (Japan) and 2004 (the Boxing Day ‘quake). Even this year’s large earthquakes were relatively safe and it showed us the many faces of smaller earthquakes too, with the swarms which struck in Nevada and California, as well as the volcano-related earthquakes in Iceland.