Scientists : Dead creatures in the ocean can influence earthquakes

(ORDO NEWS) — The Hikurangi subduction zone is the largest fault in the vicinity of New Zealand, capable of generating earthquakes of magnitude 8 and above.

A new study published in the journal Lithos shows that even the tiniest ancient marine organisms can have a very significant impact on the next seismic event.

Scientists studying the region have found that calcite deposits left by masses of single-celled marine organisms tens of millions of years ago can control the level of movement and friction between the Pacific Plate and the Australian Plate.

The researchers explain that the key to this lies in whether this calcite is able to dissolve. If so, then the plates can slide past each other more easily; if it doesn’t, it blocks the plate’s movement, blocking the energy, which is later released in a sudden surge.

“Calcite dissolves faster when it is under high stress and when the temperature is cooler,” says structural geologist Carolyn Boulton of the University of Wellington, New Zealand.

“It dissolves more easily at low temperatures say, at room temperature.

But as the temperature rises, it becomes more difficult to dissolve say, deeper in the earth.”

Deep in the subduction zone, the temperature gradually increases with depth, rising by about 10ºC per kilometer. Calcite shells that do not dissolve far below the surface could have had a significant effect on fault movements.

The fault itself is difficult to reach and requires expensive drilling equipment to access, so the researchers used exposed layers of limestone, mudstone and siltstone on the local coastline – southeast of Martinborough, on the North Island – as a proxy.

The rocks there contain calcite of marine organisms that are mostly of the type known as foraminifera (including but not limited to plankton). The next questions are how much of this calcite is in the subduction zone and what condition it is in.

“The amount and behavior of calcite in these organisms is a big piece of the puzzle of how big the next earthquake could be,” Boulton says.

Geologists know less about the Hikuranga subduction zone than other faults in New Zealand because it cannot be studied up close.

Records of previous earthquakes are not as complete, and knowledge of their condition is not as thorough, which makes it difficult to predict the next major earthquake.

Researchers say there is a 26 percent chance of a major earthquake over the next 50 years along this fault that could trigger a large tsunami (there is evidence of previous earthquakes all along the coast of New Zealand).

All sorts of factors come into play, but the study shows how plate movements can be slow and weak or fast and large – and the more we know about the accumulation of calcite underwater, the more we can understand what will happen next.

“Just think, these tiny, long-dead organisms can influence the mechanical interaction of two huge tectonic plates,” Boulton says.

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