The GeoNet project,
which monitors quakes in New Zealand, recorded a Magnitude 7.1
Earthquake at a depth of 90km, about 105 km to the northeast of North
Island, slightly before 2.30 am New
Zealand Time on Friday 5 March 2021 (slightly before 1.30 pm on
Thursday 4 March, GMT.
There are no reports of any damage or casualties associated with this
event, but it was felt across much of New Zealand, and the National Emergency Management Agency issued a tsunami warning for the east coast of North Island.
New Zealand is located on the boundary beneath the Australian and Pacific Plates. Beneath the islands the Pacific Plate is being subducted beneath the Australian Plate. This causes a great deal of friction which causes Earthquakes where the boundary between the two plates is close to the surface; this is to the east of North Island, but onshore on South Island, where it can lead to strong Earthquakes. Technically such quakes also occur where the plate margin is deeper, but these are felt less strongly as the rocks between the boundary and the surface absorb much of the energy, making strong tremors much less frequent on North Island. As the Pacific Plate sinks deeper into the Earth it is partially melted by the friction and the heat of the planet's interior. Some of the melted material then rises through the overlying Australian Plate, fuelling the volcanoes of New Zealand.
Earthquakes
along subductive margins are particularly prone to causing tsunamis,
since these often occur when the overlying plate has stuck to the
underlying plate, being pulled out of shape by its movement.. Eventually
the pressure builds up to far and the overlying plate snaps back,
causing an Earthquake and a tsunami.
Witness
reports of Earthquakes can help scientists to understand these events,
and the underlying geologic processes that cause them. If you have felt
an Earthquake in New Zealand then you can report it to the GeoNet here.
See also...
