Fig. a) Diagram of the Hikurangi subduction zone (the red line indicates the profile in panel b)
Fig. b) Position of the IODP oceanic drilling (green line) and of the subduction fault (red line)
Fig. c) What the clay-rich fault material looks like.
a) Sketch of Hikurangi subduction zone (red line is the profile shown in panel b).
b) The location of the IODP drilling mission (green line) and the subduction fault (red line).
c) The appearance of the clay-rich fault material.
Fig. a) Subduction zone: the yellow star indicates the position where earthquakes that can cause tsunami waves originate.
Fig, b) Magnification of the seismic slip front: velocity evolution (red line), shear stress (black line), water pressure (blue line) inside the fault.
a) Subduction zone, the yellow star indicates where tsunami earthquakes might nucleate.
b) Zoom at the front of a propagating earthquake: evolution of seismic velocity (red line), shear stress (black line) and water pressure (blue line) inside the fault.
Clayey sediments from the New Zealand subduction margin of Hikurangi, an area in the past site of tsunamis and earthquakes, analyzed with a new method at the INGV laboratories
The clayey materials of the faults present in the subduction zones, i.e. where a tectonic plate slides under another plate, retain a "water cushion" inside them and this causes them to favor earthquakes potentially capable of causing tsunamis . This is the result of the study "Fluid pressurisation and earthquake propagation in the Hikurangi subduction zone”, conducted thanks to the collaboration between the National Institute of Geophysics and Volcanology, the Universities of Pisa and Padua, and the University College London, on some samples from the Hikurangi area in New Zealand. The work was published by 'Nature Communications'.
“In Subduction Zones” explains Stefano Aretusini, INGV researcher and first author of the study, “Seismic sliding that occurs at shallow crustal depths can lead to the generation of tsunamis and earthquakes. Due to the experimental difficulties in deforming the materials present in these areas, the physical processes that reduce the resistance of the thrust to which the fault is subjected are poorly understood. Analyzing in the laboratory the behavior of samples taken in the Hikurangi subduction zone", continues the researcher, “We found that the clays present tend to have low resistance to seismic forces due to the pressurized water they hold inside them”.
To study the behavior of these clays coming from the fault, the researchers conducted experiments on the numerous samples collected during the international drilling campaign "Integrated Ocean Drilling Program 375" carried out in 2018 off the North Island of New Zealand, in which he participated Professor Francesca Meneghini of the University of Pisa, second author of the published work.
In detail, the samples of the rocks present inside the fault were pulverized.
The powders were tested in the High Pressure and High Temperature Laboratory (HP-HT) of the INGV through a sophisticated apparatus, SHIVA (Slow to High Velocity Apparatus) financed by the European Research Council on a project by Giulio Di Toro, of the of Padua and co-author of this study, and reproduces the "engine" of earthquakes (the fault) allowing to observe what happens inside the earth's crust and the deformations undergone by the rock under very strong pressures. Inside SHIVA, the dusts were analyzed through a new method which allowed them to keep water inside them while they were deformed at the speeds typical of earthquakes.
Through the control tests conducted on a material whose characteristics are known, a Carrara marble powder, the researchers came to the conclusion that these clays favor the seismic sliding of the fault precisely because of their ability to retain water, a characteristic that the makes it 'weak'.
"When I decided to participate in the oceanographic expedition”, says Francesca Meneghini, “I immediately contacted my colleagues at INGV and the University of Padua, with whom I have been collaborating for years, certain that it was a unique opportunity to test the new experimental technique developed at the Institute and make a further contribution to our knowledge of seismic phenomena" .
"Subsequent developments of this research”, concludes Stefano Aretusini, "They will be those of analyzing other types of materials sampled during the mission with the same method to try to understand which of them can favor the seismic shaking process once they arrive at the subduction zone".
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From the seas of New Zealand an important discovery on the relationship between clayey materials and earthquakes
Clayey sediments from the Hikurangi subduction margin in New Zealand analyzed with a new method. The area in the past was the site of tsunamis and earthquakes.
The clayey materials of the faults present in the subduction areas, that is, where a tectonic plate slides under another plate, retain a "water buffer" inside them. This means that they favor earthquakes potentially capable of causing tsunamis. This is the result of the study "Fluid pressurization and earthquake propagation in the Hikurangi subduction zone" conducted thanks to the collaboration between the Italian Istituto Nazionale di Geofisica e Volcanologia, the Universities of Pisa and Padua, and the University College London, on some samples from the Hikurangi area in New Zealand. The work was published in Nature Communications.
"In subduction zones", explains Stefano Aretusini, researcher at INGV and first author of the study, "the seismic sliding that occurs at shallow crustal depths can lead to the generation of tsunamis and earthquakes. Due to the experimental difficulties in deforming the materials present in these areas, the physical processes that reduce the resistance of the thrust to which the fault is subjected are poorly understood. Analyzing in the laboratory the behavior of the samples taken in the Hikurangi subduction zone”, continues the researcher, "we discovered that the clays present tend to have a low resistance to seismic movement due to the pressurized water they retain inside".
To study the behavior of these clays coming from the fault, the researchers conducted experiments on the samples collected during the international drilling mission "Integrated Ocean Drilling Program 375" carried out in 2018 off the North Island of New Zealand, attended by Professor Francesca Meneghini of the University of Pisa, second author of the published work.
In detail the samples of the rocks present inside the fault have been pulverized. The powders have been tested in the High Pressure and High Temperature (HP-HT) Laboratory of the INGV through a sophisticated apparatus, SHIVA (Slow to High Velocity Apparatus), funded by the European Research Council on a project by Giulio Di Toro, from University of Padua and co-author of this study, and reproduces the "engine" of earthquakes (the fault) allowing to observe what happens to the interior of the earth's crust, with the deformations that the rock undergoes under high pressures.
Inside SHIVA, the powders have been analyzed using a new method to retain the water inside them while they are deformed at the typical speeds of earthquakes".
Through the control tests conducted on a material whose characteristics are known, a Carrara marble powder, the researchers came to the conclusion that these clays favor the seismic slip of the fault precisely because of their ability to retain water, a characteristic that makes them 'weak '.
"When I decided to participate in the oceanographic expedition”, says Francesca Meneghini, "I immediately contacted my colleagues from INGV and the University of Padua, with whom I have been collaborating for years. I was sure it was a unique opportunity to test the new experimental technique developed at the Institute and make a further contribution to our knowledge of seismic phenomena”.
“The subsequent developments of this research”, concludes Stefano Aretusini, “will be to analyze with the same method also other types of materials sampled during the mission to try to understand which of them can favor earthquake slip once they are transported into the subduction zone”.
link: