Hikurangi subduction zones is the most prominent fault in New Zealand. They are capable of creating Megathrust earthquakesThese rumble at magnitudes 8 to above. Recent research suggests that ancient, tiny marine organisms could play a key role in the next seismic event.
Researchers have discovered that the region is rich in biodiversity. calcite depositsThe friction and movement between the Australia and Pacific plates can be controlled by a large number of single-celled marine organisms that existed tens to millions of years ago.
Researchers explain that the key to understanding whether this calcite can dissolve is whether it is or not. It can dissolve, which is like a sugar cube in tea. If it does, plates slide past each other much more easily. If it doesn’t, it blocks plate movement and locks up energy that will be released later in a sudden burst.
Calcite melts more quickly when it is highly stressed or when the temperature is lower. says structural geologist Carolyn Boulton, from Te Herenga Waka – Victoria University of Wellington in New Zealand.
“It dissolves more easily at low temperatures – say, room temperature. But it gets harder to dissolve as temperature goes up – say, deeper in the Earth.”
Down in the depths of the subduction zone, the temperature increases gradually with depth, warming by around 10º C for every kilometer. Failure to dissolve calcite shells deep below the surface may have an important effect on fault movement.
The fault itself is difficult to get to and requires expensive drilling equipment to access, so the researchers have been using the exposed layers of limestone, mudstone and siltstone on a local shoreline – south-east of Martinborough, on the North Island – as a proxy.
There is calcite that has been extracted from marine organisms. The rocks are mostly of the type known as Foraminifera(including plankton and others). The next questions will be how much of this calcium is located in the subduction area and what its state.
“The behavior and amount of calcite in these organisms are a large piece of the puzzle about how big the next earthquake might be.” Boulton.
Because the Hikurangi subduction area can’t be inspected up close, geologists have less information about it than other faults in New Zealand. It is difficult to predict the next big earthquake because the record of past quakes isn’t as complete and its condition isn’t as well-known.
Researchers estimate that there is a 26 percent chance for a large earthquake to occur in the next 50-years along this fault. This could potentially generate a tsunami (there are evidence of previous ones all along New Zealand’s coast).
All kinds of factors are at play, but the study shows how plate movements can be slow and slight, or quick and large – and the more we know about the build-up of calcites underwater, the better we’ll be able to figure out what’s coming next.
“Just think about how these small, long-dead organisms might affect how two enormous tectonic plate interactions mechanically.” Boulton.
The research has been published in Lithos.
