
This image shows the location of the earthquake in relation to the islands. The earthquake epicenter, shown by a large black circle, was located on the Pacific tectonic plate near its boundary with the Australian plate (southwest corner of map). Dozens of magnitude 4 and 5 aftershocks, shown by open circles, followed the initial earthquake, continuing until at least September 30th. The knee-shaped area of deep water is the Tonga Trench, a deep canyon on the edge of the Pacific plate. The trench and associated faults are forming as the Pacific Plate moves westward, sinking beneath a complex series of smaller plates on the edge of the Australian plate, the shallower area in the lower left corner of the image. The region around the Tonga Trench is one of the most active earthquake regions in the world, said the USGS.