The week was particularly active in terms of both number and magnitude of earthquakes, with notable tremors occurring across the globe.
The United States Geological Survey’s real time earthquake map for the week shows some 148 events of greater than or equal to magnitude 4.0 (≥M4.0): of these, 40 were ≥M5.0.
Distribution of Major Earth Tremors
As usual, the majority of the earthquakes follow an expected pattern, tracing the boundaries of the Earth’s major tectonic plates.
A notable exception is the M4.3 earthquake which struck eastern Kentucky, far from any plate boundaries and within a largely stable continental interior.
This was most likely the result of movement along a major fault line associated with the Appalachian Mountains.
Filtering the earthquakes by size, there’s the expected strong emphasis on the Pacific and on Indonesia, although continental collision between the Indian and Eurasian plates was responsible for the M6.8 and its aftershocks which formed a cluster in northern Myanmar (Burma).
There were also four earthquakes of between M5.1-M5.2 along ocean ridges. Another unusual occurrence was an M5.1 in an intraplate setting south of Australia, although (perhaps because of its remote location) no information is available as to its cause.
The Week’s Largest Earthquakes
The week’s large earthquakes showed a disproportionate focus on the eastern edge of the Pacific Ocean: with the exception of the Myanmar/Burma tremor, all of those with a magnitude of at least M6.0 occurred along this margin. The biggest, which measured M7.4, and one of its aftershocks (reaching M6.5) occurred just off the coast of Guatemala, where the Cocos Plate is subducting beneath Central America.
Other major earthquakes occurred in the south eastern Pacific off Chile, where an M6.0 was recorded close to the triple junction between the South American, Nazca and Anatarctic plates, and in the extreme north of the same ocean where an M6.2 just off Vancouver Island (on the Cascadia subduction zone) on the 8th of November was followed by an M6.4 off Alaska four days later.
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