2009 Tonga earthquake
The 2009 Tonga earthquake occurred on March 19, 2009, and measured 7.6 Mw , with a depth of 31 kilometres (19 mi) and a maximum Mercalli intensity of V (Moderate).
Tectonic Setting
The Earthquake occurred as the result of shallow reverse faulting on or near the subduction zone interface between the Pacific and Australian plates to the southeast of Tonga. Focal mechanism solutions indicate that rupture occurred on either a south-southwest- or a north-northeast-striking, moderately dipping reverse fault. Of these two possible fault orientations, finite-fault modeling of globally recorded seismic data is more consistent with slip on the south-southwest-striking fault. At the location of the earthquake, the Pacific Plate moves west with respect to the Indo-Australian plate at a velocity of about 77 mm/yr, beginning its descent into the mantle at the Tonga Trench, just east of the earthquake. The broad-scale tectonics of the earthquake region are dominated by the relative convergence of the Pacific and Australia plates. The eastern edge of the Australia plate may itself be viewed as a collection of small microplates whose relative motions help to accommodate the overall Pacific-Australia convergence and associated back-arc spreading. In terms of numbers of earthquakes, the broad-scale Australia-Pacific plate boundary is one of the most active in the world. Earthquakes occur on the thrust fault boundary between the Australia and Pacific plates, within the Pacific Plate, and within and on the boundaries of the small microplates that together compose the eastern edge of the overall Indo-Australian plate. On the basis of currently available information, including the earthquake depth and the relative steepness of focal mechanism solution nodal plane dips, it is inferred that the earthquake of March 19, 2009, occurred within the subducting Pacific Plate, rather than on its overlying thrust interface with the Indo-Australian plate. There also was an 8.0 event in May 2006, which resulted in one injury, some minimal damage, and a tsunami that was recorded as far away as La Push, Washington. The 2006 earthquake was likely an intraplate event.
Tsunami
A small tsunami was generated with wave heights up to 10.4 cm at Iquique, Chile, 17.3 cm at Rarotonga, Cook Islands, 5.7 cm at Suva, Fiji, 27 cm at Santa Cruz, Galapagos Islands, 10 cm at Honolulu, 18.6 cm at Kahului, and 9.4 cm at Nawiliwili, Hawaii, 20.3 cm at Nuku Hiva, and 14.5 cm at Hiva Oa, Marquesas Islands, 10 cm at Napier, New Zealand, 8.7 cm at Niue, 22.8 cm at Callao, Peru, and 10.7 cm at Port-Vila, Vanuatu.
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