A mountainous mass of igneous rock beneath the coast of southern Japan could act as a kind of magnet or lightning rod for massive earthquakes.
Tectonic energy appears to be deflected by megaquakes at various points along its side, according to a new 3D visualization of the feature known as Kumano Pluto.
This could facilitate scientists better predict the impact of large quakes within the region, also as better understand how these igneous masses interact with tectonic activity.
“We cannot predict exactly when, where, or how big the future earthquakes will be, but by combining our model with the monitoring data, but we can estimate the processes of near future,” says Geophysicist Shuichi Kodaira of Japanese Agency for Marine-Earth Science and Technology in Japan.
“This will provide very important data for the Japanese public to prepare for the next major earthquake.
Evidence of the Kumano pluton was first revealed in 2006. It is, as the name suggests, a rocky feature known as a pluton: an igneous rock intrusion that displaces rock underground, slowly cools, and hardens into a large chunk.
Seismic imaging revealed that something of a different density than the surrounding rocks was present in the Nankai subduction zone; This is the region along which one tectonic plate slides under the edge of another, accompanied by increased seismic and volcanic activity. Numerical simulations helped reveal that the chunk was plutonic.
But the true extent remained unexplored. Now a team of researchers has mapped the entire Kumano pluton using 20 years of seismic data from the Nankai subduction zone.
Quakes and tremors, while destructive, can even be very powerful tools. Quakes are actually pretty wonderful things. They spread from their point of origin, spread across the planet, and bouncing around.
The way these seismic waves propagate and reflect off certain materials permits seismologists to map structures that we can’t see underground.
It was painstaking work, involving not only millions of seismic records from the Japan Seismic Sensor Network, but also those from other previous scientific studies, to obtain the largest seismic dataset ever created.
The large amount of data compiled by the team on the Nankai subduction zone was fed into the LoneStar5 supercomputer at the University of Texas at Austin to generate a high-resolution 3D model of Pluton. In a fascinating way, it revealed features that we had never seen before.
The model shows that Pluton’s weight causes the Earth’s underlying crust to bend under strain, bulging slightly upwards. Surprisingly, the pluton appears to provide a path for groundwater to seep beneath the Earth’s crust into the upper mantle, exacerbating the bending of the Earth’s crust.
Because the Kumano pluton is so dense and rigid, it also likely plays a role in tectonic activity.
Huge earthquakes with magnitudes greater than eight originated at the flanks of the pluton in 1944 and 1946. Given that subducting slabs are notably sensitive to variations in structure, the pluton is probable having a profound impact on both the geometry and tectonic activity in the region.
The team hopes that their discovery sends in-depth research investigations into subterranean structures that can hide in other subduction zones.
“The fact that we can make a discovery in an already well studied area so great, I think of the opening of the eyes on what I could expect in places that could be less well monitored,” says Geophysicist Adrien Arnulf of the University of Texas Institute for Geophysics.
The research has been published in Nature Geophysics.