The New Year crept in quietly, from a seismological perspective, with just one exception – a magnitude 7.5 (M7.5) earthquake in the northern Pacific off the coast of Alaska. That apart, the week saw just 13 earthquakes of M5.0 or greater, most in the Pacific but with two in a mid-ocean ridge setting in the Indian Ocean.
There were, of course, other earthquakes: a glance at the map shows 98 tremors of ≥M4.0. Again, these were largely focussed on the Pacific margin, although a line of tremors traces the southern boundary of the Eurasian plate as it collides in turn with the Australian, Indian, Arabian and African plates.
Largest Earthquake: Alaska
Appearing around 120 times larger than the week’s next-biggest earthquake on a seismograph, and releasing over 1400 times as much energy, the M7.5 quake which struck off the Pacific coast of Alaska is by some way the major seismic event of the year so far. The tremor and its aftershocks took place on the Queen Charlotte section of the Queen Charlotte-Fairweather transform boundary, which runs between the two subduction zones of Cascadia to the south and the Aleutian megathrust.
Although a tsunami warning was issued (and later withdrawn) only a small tsunami occurred. This was down to the nature of the fault which moves laterally rather than vertically: vertical movement displaces large volumes of water which can, under certain circumstances, generate tsunamis.
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