When the Kamchatka earthquake off far-east Russia hit late in July, alerts went off across the world, including at the 24/7 GeoNet National Geohazards Monitoring Centre in Wellington. During the first minutes, as seismometers along the coastlines of the Pacific registered the passing wave of seismic energy, staff monitored live data feeds while teams at the US Geological Survey worked quickly to assess the earthquake’s magnitude, from an initial M8 to M8.8.
It soon became clear the earthquake had likely deformed the seabed enough to trigger a planet-scale tsunami that would eventually reach New Zealand. “The difference between 8 and 8.8 is about 10 times as much energy,” says Graham Leonard, lead scientist for natural hazards and risks at Earth Sciences New Zealand.
Thankfully, the New Zealand team had time on its side. While earthquake scientists mapped the slip along the fault plain, showing most of it happened about 20km deep in the Earth’s crust, others worked out how this would translate into tsunami-generating forces on the seabed.
As the tsunami hit tide gauges in the northwest Pacific, people in Wellington watched real-time data showing the wave’s amplitude. The tsunami expert panel was called in to estimate the wave size New Zealand could expect some 13 hours after the earthquake. Some of the models the team uses run on supercomputers, Leonard says, and can “basically model the tsunami faster than it can move through the ocean”.
New Zealand is a member of the Pacific Tsunami Warning Center, which is based in Hawaii, and has contributed 12 DART (deep-ocean assessment and reporting of tsunami) buoys. They essentially track the weight of the water column above them and transmit the data via satellite to the centre, which then provides confirmation of wave heights and forecasts of arrival times.
Some parts of the Pacific saw waves up to five metres; more than two million people were evacuated from the shore. When the tsunami arrived at our coastlines, with the highest wave at 55cm, nobody needed to move. But the team forecasted that higher waves, built up to 70cm after the first tsunami bounced off the South American coast, would arrive at the Chathams a day later.
Leonard says smaller waves don’t necessarily mean no danger. “A regular wind wave or even a storm surge wave has a period of seconds. It just goes ‘sploosh’ and it’s done. A tsunami wave has a period of minutes, often tens of minutes. What you really have is a surge of water arriving and it just keeps coming and flooding in for 10 or 20 minutes and then receding for 10 or 20 minutes – then doing the same thing again for hours and hours.”
He uses the analogy of a river crossing. “Even if the river isn’t very deep, it’s a surge of high-energy water that can knock you off your feet. Would you wade across a mountain river that was 50-70cm deep?”
He says one of the synergies of the recent merger of ex-crown research institutes and other organisations is that it brings together people who work on risks from natural hazards, weather and climate and can deliver multi-hazard impact-based warnings quickly, with “one cohesive approach”.
Although this improves tsunami warnings triggered by distant earthquakes, the Kamchatka megathrust was also a reminder that this can happen here as well.
The Pacific region is prone to powerful earthquakes because it’s fringed by interlocking boundaries between tectonic plates, known as the Ring of Fire. Most of the powerful earthquakes recorded in modern history happened in this region. One of these plate boundaries, the Hikurangi subduction zone along the east coast of the North Island, has the potential to rupture in a large earthquake.
There’d be no time to wait for official tsunami alerts, Leonard says. “If an earthquake lasts a minute or more or is so strong that it’s hard to stand up, just make your way to the nearest high ground or as far inland as you can.”
