Researchers have uncovered an intriguing factor that could affect the size of the next big earthquake in the Hikurangi subduction zone in New Zealand. They found that the fossils of tiny, ancient organisms that lived tens of millions of years ago could influence the next seismic event in the area.
According to Interesting Engineering, the Hikurangi subduction zone in New Zealand is the largest plate boundary fault that runs off the east coast of the north island where the Pacific Plate and Australian Plate meet. Experts say that the region could generate massive earthquakes stronger than magnitude eight.
Examining the Hikurangi Subduction Zone to Predict Earthquakes
Researchers did a close examination of the Hikurangi subduction zone to predict earthquakes. Dr. Carolyn Boulton led the team from the Te Herenga Waka-Victoria University of Wellington, wherein they investigated a rocky bluff on the Hungaroa fault on the margins of the subduction zone.
Among the rocky bluff include layers of limestone, mudstone, and siltstone located near Tora, which is about 21 miles (35 kilometers southeast of Martinborough. Investigating the area provided a convenient indication of the events in the offshore subduction zone.
They found that rocks like those were deposed on the seafloor between 35 and 65 million years ago, New Atlas reported. In these deposits are large amounts of calcites, a common carbonate mineral. But this time, it comes from the shells of tiny, ancient marine organisms that could play a bigger role than expected.
Calcites can act like a lubricant for the two tectonic plates in the subduction zone if the calcites dissolve in high enough quantities. This could result in both tectonic plates sliding easily without triggering noticeable earthquakes at the surface. On the other hand, the fault line could also lock up and store energy than can be released as a larger earthquake if calcites do not dissolve.
The Amount of Calcites in the Subduction Zone Could Influence the Size of Earthquakes
"Calcite dissolves faster when it's highly stressed and when temperatures are cooler," structural geologist Carolyn Boulton said in a statement. He added that calcites dissolve more easily at low temperatures, and it gets harder to dissolve them at high temperatures, like in deeper Earth.
The temperature in the depths of the subduction zone gradually increases with depth and warms up by around 10 degrees Celsius for every kilometer, Science Alert reported. Calcites that did not dissolve beneath the surface could significantly influence the movements of the faults.
Researchers used the exposed layers of limestone, mudstone, and siltstone as a proxy for studying the fault, which is difficult to get to unless using expensive drilling equipment. The rocks in this area contain calcites from tiny organisms called foraminifera. The amount of calcites in the subduction zone greatly determines how large the next earthquakes will be.
Even with less knowledge about the Hikurangi subduction zone than other faults in New Zealand because of its inaccessibility, researchers estimate that there is a 26% chance of a large earthquake in the next 50 years along this fault, which could generate a large tsunami based on evidence from previous ones in New Zealand coast.
The more information there is about the build-up of calcites underwater, the better will scientists can figure out the next seismic event. The research, titled "Observational and Theoretical Evidence for Frictional-viscous Flow at Shallow Crustal Levels," is published in Lithos.
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