So, welcome to the New Year. In one way, this New Year’s week was relatively quiet seismically speaking: in another, not so.
The quiet way is the way of numbers, as represented on the United States Geological Survey’s real time earthquake map.
The map, which shows tremors of all magnitudes in the US and its territories and those of at least magnitude 4 (≥M4.0) elsewhere, barely strayed from its typical pattern. There were no earthquakes in excess of M7.0; just two ≥M6.0; and 96 ≥M4.0, all out of a total of just over 1500 seismic events.
The not-so-quiet element involves not the planet itself, but the inhabitants on it and the way we interact and play our part in the Earth system.
The Week’s Biggest Earthquake: M6.7, North-Eastern India
The collision between the (relatively rapidly-moving) Indian subcontinent and the Eurasian continent is a highly significant one. It raised (and continues to raise) the Himalayas and mountain ranges to the east and the west, creating a zone of crumpled crust that stretches from Afghanistan in the west to Myanmar in the east.
With such rapid convergence rates (they vary but the figure of 38mm per year quoted by Yeats is typical) there’s increased strain and, as a direct consequence, a high risk of earthquakes. In the east of this diffuse collision zone, the two plates slide past one another creating a series of broadly north-south trending, largely strike-slip fault zones. It was along one of these that that the week’s largest earthquake occurred.
The M6.7 which struck on January 3 wasn’t, in the great scheme of things, a major seismic event., but it caused several deaths and injuries and injuries, as well as considerable damage. The reason? The same as usual in the region — that, as the USGS notes in its earthquake summary: “the population in this region resides in structures that are highly vulnerable to earthquake shaking”.
M5.1 Earthquake, North Korea
At M5.1 the ‘earthquake’ which struck in North Korea may not have been large — but it certainly brought in the first week of 2016 with a bang. Literally.
Yeats, in his comprehensive reference book on the planet’s fault zones, doesn’t give North Korea a mention. That’s because it’s located well away from those crucial earthquake zones and usually subject to nothing more than the odd quiver that might occur anywhere.
Its tectonic stability, however, isn’t matched politically.
The USGS notes in its (currently sparse) earthquake summary that: “We have changed the classification of this event to an nuclear test based on Ambassador Rice’s statements at the United Nations Security Council Stakeout”.
The link to Ambassador Rice’s statement doesn’t work (make of that what you will, conspiracy theorists) but we learn from the news that North Korea is claiming to have exploded a test hydrogen bomb. Whether the size of the blast is consistent with an H-Bomb rather than any other type of nuclear explosion remains the subject of debate. But we can be pretty certain that this earthquake, like others before it in this country, is man-made.
US Earthquakes: Guess Where?
Meanwhile, in the United States, 2016 carries on exactly where 2015 left off — with a swarm of anthropogenic earthquakes in central Oklahoma and northwards into Kansas. The largest of these, at M4.2, was outstripped (just) by an M4.4 in California, so can’t claim to be the largest in the US. And really there’s not much new to add to what we’ve been saying for years, except that the chances are I’ll be writing pretty much the same thing in 2017.
Last Thoughts: It’s All About Us
The biggest earthquake of the week wasn’t man-made, but man-made structures contributed to its impact. And the other featured earthquakes, both in areas where naturally-induced earthquakes are, if not unknown, small and infrequent, were unquestionably the result of human activity. Surely food for thought, there?