The United States Geological Survey
detected a Magnitude 6.8 Earthquake at a depth of 10 km, about 86 km to
the northeast of the island of Niuatoputapu (sometimes known as Traitor's Island or Keppel Island) at about 10.00 pm local time
on Friday 3 November 2017 (about 4.00 am on Saturday 4, GMT).
While this was a large quake, it was unlikely to present any danger due
to its distance from shore, though it was felt on the islands of Upolu in Samoa and Tutuila in American Samoa.
The islands of Tonga and Samoa lie on opposite sides of the boundary between the Pacific and Australian Tectonic Plates. The Pacific Plate is being subducted beneath the Australian Plate along the Tonga Trench, which forms the boundary between these two plates, with the volcanic islands that make up the Tonga archipelago being formed as the subducting plate is melted by the heat of the planet's interior, so that lighter minerals rise up through the overlying plate as liquid magma, which fuels the volcanoes that build the islands. This subduction is not a smooth process, with the two plates constantly sticking together until the pressure generated by their movement builds up sufficiently to break them apart, causing a sudden forward jerk we experience as an Earthquake.
See also...
The approximate location of the 3 November 2017 Tonga Earthquake. USGS.
The islands of Tonga and Samoa lie on opposite sides of the boundary between the Pacific and Australian Tectonic Plates. The Pacific Plate is being subducted beneath the Australian Plate along the Tonga Trench, which forms the boundary between these two plates, with the volcanic islands that make up the Tonga archipelago being formed as the subducting plate is melted by the heat of the planet's interior, so that lighter minerals rise up through the overlying plate as liquid magma, which fuels the volcanoes that build the islands. This subduction is not a smooth process, with the two plates constantly sticking together until the pressure generated by their movement builds up sufficiently to break them apart, causing a sudden forward jerk we experience as an Earthquake.
Diagram showing subduction along the Tonga Trench, and how this feeds the volcanoes of the Tonga Volcanic Arc. York University.
Witness
accounts of Earthquakes can help geologists to understand these events,
and the structures that cause them. The international non-profit
organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.
See also...
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