New Zealand was already hit by a massive earthquake around this time last year, the Kaikoura earthquake, but that quake registered only 7.8M. Despite the sheer power of the quake luckily only a few people were killed or injured. Yet researchers have asked the New Zealand public to remain vigilant and prepare for a quake that could be much more powerful.
Earthquakes are rated on a logarithmic scale. This means that although the Kaikoura earthquake which occurred last year was a 7.8, and another earthquake in New Zealand (the Christchurch earthquake of 2011) was a 6.3, the Kaikoura earthquake actually released approximately 180 times as much energy as the 2011 quake. The 9.0 earthquake that scientists are warning about could be 11,000 times as powerful as the Christchurch quake.
It should be noted that these magnitudes are not on the Richter scale, a system of calculating earthquake intensity that was used for much of the 20th century. The Richter scale was actually abandoned by seismologists because it worked primarily on earthquakes which occurred in California, and was of little use when trying to measure intense quakes like the magnitude 9 quake that hit Japan in 2011. Seismologists now use a new system called the “momentum magnitude scale”, which can detect quakes on the other side of the Earth.
New Zealand sits right on top of a subduction zone. A subduction zone is where two of the Earth’s tectonic plates crash together. At these subduction zones, one of the plates bends while the other plate slides underneath it and is pushed down into the mantle of the earth. The crashing together of these two plates is responsible for the creation of mountain regions, and also earthquakes.
Much like rubbing two pieces of sandpaper together, when two chunks of plates crash together the motion isn’t smooth. The crust of the earth get stuck in certain areas, and stores up energy. When this energy is finally released it is released through a massive earthquake. Subduction zones are where the largest earthquakes ever have occurred, such as a magnitude 9.2 earthquake in Alaska, and a magnitude 9.5 earthquake in Chile. The size of the fault line near the subduction zone is directly related to the strength of the earthquake in question, with larger subduction zones causing larger and more powerful earthquakes.
As it happens New Zealand is directly on the Hikurangi subduction zone. The oceanic Hikurangi plateau is currently in the process of sinking into the mantle found beneath the Indo-Australian plate. The friction of these two plates is building up a lot of stress, and many scientists are worried that a massive quake could soon follow. A debate is currently raging about just how large a role the Hikurangi subduction zone played within last year’s earthquake, but it is generally agreed that the fault line is moving and building up stress energy.
The Ring of Fire is made up of subduction zones that encircle the Pacific ocean. Photo: Gringer via Wikimedia
When the plate finally ruptures it might create an incredibly powerful record-breaking earthquake. Furthermore, the plate’s position in the Pacific Ocean means that it has the potential to create a massive tsunami in addition to the initial earthquake. The tsunami would hit the north New Zealand island in as few as seven minutes and would hit the South New Zealand island in 10 to 30 minutes.
Geologists are saying that people should be prepared for a disaster similar to the 2011 earthquake in Japan, which killed around 16,000 people as a result of the earthquake and ensuing tsunami which hit the country’s northeastern coast. (To make matters worse, this also led to the disaster at the Fukushima nuclear plant.)
Urusla Cochran, a scientist from GNS New Zealand ( a geoscience center), has said it is important that people not think the Kaikoura quake was “the big one”. Cochran wants to drive home the importance of disaster preparedness.
Scientists from around the globe are currently studying the Hikurangi plate boundary, to get more information about the possible threat it poses to New Zealand and to hopefully help authorities forecast a quake so that damage can be kept to a minimum.
“We are deploying instruments onto the seafloor to measure plate movement, drilling into the fault to look at its properties, seismic surveying to get an image of the physical conditions on the plate boundary, investigating more of the onshore and offshore geology to find evidence of past earthquakes,” says Cochran. “…Don’t be scared, be prepared.”
New Zealand is not the only area of the world that should be concerned about the possibility of intense earthquakes. The warning about New Zeland’s earthquake troubles comes only a couple weeks after a report was published in Nature Geoscience that implied the Cascadia Subduction Zone, located along the coast of Washington and Oregon, could rupture again and sooner than most scientists expected. Furthermore, the fault line is also more likely to generate a more massive quake than many researchers expected.
The Cascadia Subduction Zone is almost 1000 km or 620 miles long and it is currently being jammed under the North American plate. This makes the subduction zone a thrust fault like the New Zealand plate, capable of producing similar damage. The energy this fault generates cannot release itself due to a massive sediment band which sits over the oceanic Juan de Fuca plate. The sediment is acting as a wedge between the two plates and preventing the subduction zone from releasing stress.
To make matters worse, the mass of sediment that forms the wedge is very compact, which means it is preventing water from getting to the plate juncture and acting as a lubricant that would allow the plates to more easily mesh. Subduction zones which are drier are usually responsible for large quakes because they are more likely to build up friction.
The fact that the quake could be so powerful means an increased risk of a massive tsunami as well. The authors of the report note that the last time a megathrust quake occurred in the region, the tsunami was so powerful it crossed the ocean to Japan. Geologists believe that the Cascadia Subduction Zone has a major earthquake approximately every 200 to 500 years, and the last major quake occurred around 1700.