Ancient Creatures May Influence a Next Great Earthquake

Oct. 10 () –

Remnants of tiny creatures tens of millions of years old may affect the size of the next destructive earthquake in the Hikurangi subduction zone, the largest fault in New Zealand.

This zone marks the boundary where the Pacific plate plunges under the Australian plate. Large earthquakes of more than 8 magnitude can be generated in the area.

Dr Carolyn Boulton, from the Victoria University of Wellington, has been leading a team of earthquake scientists studying a rocky cliff on the Hungaroa Fault, located on the margins of the Hikurangi subduction zone.

Limestone, shale and siltstone layers in the cliff near Tora, about 35 km southeast of Martinborough, are a useful indicator of what’s happening in the subduction zone offshore, Boulton says. it’s a statement.

Rocks similar to those on the cliff were deposited on the seabed between 35 and 65 million years ago, but their location makes them difficult to study. Instead, scientists they can look at rocks on land to find out more about what happens under the sea.

“All the rocks contain calcite from ancient single-celled marine organisms, mainly foraminifera, such as plankton. We have found that calcite from those small organisms can affect movement in the subduction zone. These tiny, long-dead organisms can affect how two huge tectonic plates interact mechanically.“, exposes Boluton.

She says that if the calcite in rocks can dissolve, like sugar in tea, the fault can be weak and slip easily without an earthquake. However, if the calcite cannot be dissolved, the fault can “lock up”, storing energy that could be released in a large earthquake.

“Calcite dissolves faster when it is highly stressed and when temperatures are cooler. It dissolves more easily at low temperatures, for example at room temperature. But it becomes more difficult to dissolve as the temperature increases, for example, deeper in the Earth“, he comments.

“In the subduction zone, the temperature rises more slowly than on land, only around 10 degrees Celsius/km. So the fault is really sensitive to what calcite does, those shells of old dead marine organisms. amount and behavior of the calcite of these organisms is a big piece of the puzzle of how big the next earthquake could be”he adds.

The Hikurangi subduction zone still harbors many mysteries for scientists to unravel, says Boulton. “Geologists studying the Alpine Fault and other faults on land can examine them up close. But seeing inside the Hikurangi subduction zone requires expensive drilling equipment. This means that our record of previous large earthquakes in the area is not as good.“.

“Our observations show that the shallow part of the subduction zone can accommodate plate motions by sliding slowly, or sliding rapidly in large, damaging earthquakes. What we really want to know is: Are there slow-sliding events that we haven’t seen?” detected?Are the rocks moving without earthquakes or are they really locked in? That will help us tell us what might happen in the next earthquake.Boulton says.

A mega-earthquake along the subduction zone could generate a large tsunami, evidence for which has been found in geological excavations and the fossil record along the east coasts of New Zealand’s North and South Islands, and through the Strait of Cook.

Scientists predict that there is a 26% chance of a major earthquake in the next 50 years on the southern margin of the Hikurangi subduction zone.

Research Results are published in the journal Lithos.