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  • Aotearoa1 New Zealand experiences a lot of geological activity – the land is right at the junction of the Australian and Pacific tectonic plates – making it a shaky place to live! The Pacific plate is being forced down (subducted2) under the Australian plate.

    GNS Science reports the country receives over 15,000 earthquakes each year but only 100–150 of the quakes are large enough to be felt. We know about the smaller movements because they are recorded by seismographs. These machines are very sensitive to earth movements, but some movements are so small and occur over time that they don’t register. These movements are called slow slip events.

    Rights: © Copyright 2014. University of Waikato. All Rights Reserved

    Tectonic plates, volcanoes and earthquakes

    Far underneath the ground we walk on, the Earth is covered with tectonic plates. You can think of tectonic plates as puzzle pieces. Earthquakes and volcanoes often happen where the pieces meet.

    Scientists were surprised to discover that large areas of land in Te Ika-a-Māui3 North Island are silently and slowly moving towards the east. The movement is very, very slow. In human terms, imagine standing at one spot and taking more than 2 weeks to move a couple of millimetres. Now you can see why slow slips weren’t even noticed in Aotearoa until 2002.

    Exploring the slow slip mystery

    Slow slips were first observed in Japan and Canada. Scientists in Aotearoa began their own observations by setting up networks of continuously recording global positioning system (CGPS) stations. There are over 50 monitoring sites across the North, South and Chatham Islands. Satellites send signals to the receivers at these sites, enabling the stations to record very precise positions on the Earth’s surface. This continuous sending and receiving allows scientists to measure even the smallest of movements – and the bigger ones too.

    GNS Science reported more than a dozen slow slip events in the first 10 years of monitoring. They have occurred in Gisborne, Hastings, Wanganui, Ashhurst, Dannevirke and Paekākāriki, and offshore in the Gisborne and Hawke’s Bay regions.

    Rights: GNS Science Limited, Lloyd Homer

    GPS station

    Tiny ground movements can be detected by using a network of continuously recording global positioning system (GPS) stations.

    A GPS station is also known as a GPS receiver.

    Why we need to monitor slow slips

    If the ground is moving so slowly, why go to the time and effort to track movements of just a few millimetres? It’s because scientists want to know if there is a relationship between slow slips and earthquakes. Sometimes it appears that slow slips can relieve the stress that builds up in fault lines. Other times it appears that slow slips increase the stress in surrounding areas and push the fault closer to rupture (breaking). Collecting data4 about slow slips provides a better understanding of this relationship. It might also help to inform models that warn us about earthquakes.

    Rights: The University of Waikato Te Whare Wānanga o Waikato

    Earth movements satellite mission

    Gathering data about the movement of the Earth’s crust is crucial to assist scientists with earthquake and hazard planning. This animated video prompts users to think about how satellites can be used to do this. It is part of the Build a satellite interactive.

    Select here to view video transcript, wrap-around resources and copyright.

    Build a satellite to track Earth movements

    Have a go at building a fit-for-purpose satellite5 to monitor slow slips! Choose the ‘Monitor Earth movements’ scenario. Once you’ve received the GNSS data, use this activity to analyse the slow slip movements around Māhia Peninsula.

    Related content

    Earthquake resources – planning pathways provides pedagogical insights and curates Hub resources into key science and technology concepts.

    The JOIDES Resolution6 research ship used expedition #375 to explore slow slips.

    Related activities

    Explore tectonic plate7 concepts by making tectonic sandwiches and tectonic jigsaw puzzles.

    Plot and interpret a graph using data from an actual slow slip event in New Zealand with Something creepy is happening.

    Useful links

    The Kaikōura earthquake in November 2016 caused a slow slip 250–600 km away from the New Zealand Aotearoa coastline on the shallow part of the Hikurangi subduction8 zone. Read this media article with Dr Laura Wallace to learn about how this earthquake has advanced scientific knowledge of slow slip events.

    Check out these GNS Science resources on slow slip earthquakes.

    Acknowledgement

    This resource has been produced with funding from the Ministry of Business, Innovation and Employment and the support of the New Zealand Space Agency.

    Rights: Crown copyright

    Ministry of Business, Innovation and Employment and the New Zealand Space Agency

    The New Zealand Space Agency, part of the Ministry of Business, Innovation and Employment, is the lead government agency for space policy, regulation and sector development.

    1. Aotearoa: The Māori name for New Zealand, meaning Land of the Long White Cloud.
    2. subduction: When tectonic plates with differing material densities collide and the denser plate is forced down under (subducts) the less dense one.
    3. Te Ika-a-Māui: The Māori name for the North Island of Aotearoa New Zealand.
    4. data: The unprocessed information we analyse to gain knowledge.
    5. satellite: Any object that orbits around another object.
    6. resolution: In microscopy, the ability to distinguish two separate points or objects as independent. The resolution of a microscope provides a measure of the level of detail it can be used to reveal. In an image, the degree of sharpness. Resolution is measured by the number of dots per linear inch in a hard-copy printout, and the number of pixels on a display screen.
    7. tectonic plate: One of several large sections of the Earth’s crust. The Earth’s surface consists of six big tectonic plates and several smaller ones.
    8. subduction: When tectonic plates with differing material densities collide and the denser plate is forced down under (subducts) the less dense one.
    Published 25 July 2022 Referencing Hub articles
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        Aotearoa

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      2. The Māori name for New Zealand, meaning Land of the Long White Cloud.

        data

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      4. The unprocessed information we analyse to gain knowledge.

        tectonic plate

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      6. One of several large sections of the Earth’s crust. The Earth’s surface consists of six big tectonic plates and several smaller ones.

        subduction

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      8. When tectonic plates with differing material densities collide and the denser plate is forced down under (subducts) the less dense one.

        satellite

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      10. Any object that orbits around another object.

        Te Ika-a-Māui

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      12. The Māori name for the North Island of Aotearoa New Zealand.

        resolution

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      14. In microscopy, the ability to distinguish two separate points or objects as independent. The resolution of a microscope provides a measure of the level of detail it can be used to reveal.

        In an image, the degree of sharpness. Resolution is measured by the number of dots per linear inch in a hard-copy printout, and the number of pixels on a display screen.