After a week with numerous large and sometimes damaging earthquakes across a range of tectonic settings, the week of 24-30 April provided a period of respite. In total, the United States Geological Survey’s real-time earthquake map lists 1,430 recorded tremors, of all magnitudes in the US and its territories and of at least magnitude 4 (≥M4.0) elsewhere. Of these, 18 were larger than M5.0 and just two ≥M6.0.
As usual, most occurred around the boundaries of the Pacific Ocean: but the mid-Atlantic saw an unusually large tremor of M5.9 in the islands of the Azores, while an intra-plate earthquake in central Russia was also noteworthy at M5.3.
The Week’s Largest Earthquake: M6.5 Papua New Guinea
The western Pacific boundary zone between the Pacific and Australian plates, with its complex pattern, varying types of boundary and reverses in the direction of subduction, regularly supplies the week’s largest earthquakes. On 23 April, an M6.5 event struck between the islands of New Britain and New Ireland, on the boundary between the North and South Solomon microplates.
The boundary at this point is complex, with regular changes of type over short distances (often a hundred miles or less). Sections of strike-slip motion alternate with spreading ridges, while subduction of the Solomon Islands plate to the south drives volcanic activity in New Britain and the Bismarck Sea. The location of the most recent tremor suggests that it may have occurred at a junction between two such sections.
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