1947 Gisborne earthquakes and tsunami

Run-up for Gisborne tsunami, 25 March
Run-up for Gisborne tsunami, 17 May

The 1947 Gisborne earthquakes and tsunami occurred east of Gisborne, offshore New Zealand's North Island. Both earthquakes are estimated to have measured at most 7.1 on the Moment Magnitude scale.[1] The first earthquake, which struck offshore Poverty Bay on 26 March is estimated to have been between 7–7.1MW, and generated a tsunami with a maximum measured run up height of 10 meters. The tsunami caused widespread damage along the north-east coast of the North Island, but was not observed outside of New Zealand.[1] Seven weeks later, a second earthquake struck offshore Tolaga Bay on 17 May, and was estimated to have been between 6.9–7.1MW. It also generated a tsunami, with a maximum measured run up height of 6 meters. Despite occurring at low tide and being less powerful the second time around, the tsunami caused small amounts of damage along the east coast and is noted for washing away construction materials ironically being used to repair damage from the previous tsunami.[1] No one died in either of the 1947 tsunamis, but the toll could have been high had they struck during summer holidays, when the beaches are crowded.[2]

Tectonic setting

New Zealand lies along the boundary between the Indo-Australian and Pacific Plates. In the North Island the displacement is mainly taken up along the Hikurangi Subduction Zone, although the remaining dextral strike-slip component of the relative plate motion is accommodated by the North Island Fault System (NIFS). Both earthquakes are believed to have occurred along the Hikurangi Subduction Zone, in close proximity to each other. Both earthquakes generated tsunami, caused by the sudden release of energy from the Earth's crust.

See also

References

  1. 1 2 3 "Gisborne tsunami, 25 March and 17 May 1947 - Tsunami - GeoNet". Info.geonet.org.nz. Retrieved 2016-02-07.
  2. ↑ "3. – Tsunamis – Te Ara Encyclopedia of New Zealand". Teara.govt.nz. Retrieved 2016-02-07.
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