North-West Pacific and the Himalayas: Earthquakes 27 February-5 March 2013

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Distribution of earthquakes of M5.0 or more, 27 february-5 March. Image credit: USGS

Distribution of earthquakes of M5.0 or more, 27 February-5 March. Image credit: USGS

The week’s earthquakes showed no great variation from the expected pattern: There were 26 tremors of at least magnitude 5 (≥M5.0) and four of ≥M6.0. Three of these took place in the Kuril Trench between Russia and Japan, and the fourth near Vanuatu in the western Pacific. As usual, the main focus was in the western Pacific, but there was also some activity along the Himalayan Front, with earthquakes ≥M5.0 in northern India, China and Tajikistan

The Week’s Largest Earthquake: M6.9 off Kamchatka, Russia

A cluster of four earthquakes occurred off Kamchatka Russia; a mainshock of M6.0 on 28 February followed by two others of M6.5 on the following day and a third of M5.3 on 4 March. These quakes represented the most significant cluster of large-magnitude earthquake this week. No other aftershocks were recorded on the USGS map.

The earthquakes were located along the Kuril Trench, a section where the Pacific plate is being subducted beneath the southward extension of the North American plate (identified by some geologists as the Okhotsk microplate). This is a typical subduction setting for earthquake activity, with frequent tremors, some of them of extremely high magnitude (the southern part of this trench was the focus for 2011’s devastating earthquake and tsunami in Japan) and backed by a volcanically-active island arc.

The Himalayas: China, India and Tajikistan

The trio of earthquakes which occurred this week in China (M5.2), India (M5.5) and Tajikistan (M5.1) are too far apart to be directly linked, but they do share an association with the diffuse zone of continental collision which caused – and continues to cause – the uplift of the Himalayan mountain range and the Tibetan plateau behind.

None of the tremors took place on the suture zone itself, but the two to the north (in China and Tajikistan) are probably associated with the many and complex thrust zones caused by the ‘crumpling’ of the rock as a result of compression. The third, to the south of the Himalayan Front Fault, is slightly more unusual as faulting here is less: but tectonic maps of the region do indeed show faulting parallel to the eastern boundary of the collision zone.

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