Posted on May 27, 2021, 10:41 a.m.
The combination of supercomputers and seismic CT scans is the latest approach scientists are using to better understand the causes of slow-slip earthquakes over the Hikurangi Subduction Zone off the East Coast.
Slow-slip events can trigger the equivalent of a magnitude 7 earthquake, but they happen so slowly that they escaped detection until about 20 years ago.
The mechanisms that govern slow-slip events are still unclear, so researchers at GNS Science and the University of Texas at Austin set out to test several theories by pairing very powerful computers with high-quality seismic data.
Their research was published in Nature Geoscience as part of a special edition dedicated to subduction zones.
“Subduction zones are the biggest earthquake and tsunami factories on the planet,” said co-author Laura Wallace, GNS Science and the University of Texas Institute of Geophysics (UTIG) .
“With more research like this, we can really begin to understand the origin of the different types of seismic behavior in subduction zones.”
Understanding the timing and likely location of a large earthquake in a subduction zone can only happen by first solving the mystery of slow-slip events, Dr Wallace said.
“One of the theories we tested, called rate-state friction, didn’t hold up as well as expected. This means that we can probably assume that there are other processes involved in modulating slow-slip events, such as pressurization and release cycles of fluids, ”Dr. Wallace said.
Lead author of the study, Adrien Arnulf of the University of Texas, said the earth’s subsurface seismic imaging data used in the research was collected off the south coast of Hawke’s Bay in 2005 as part of a survey funded by the New Zealand government. Applying next-generation techniques to this data had provided a whole new view of parts of the Hikurangi Subduction Zone.
“It has been turned into detailed images using techniques similar to those used in medical imaging, so geoscientists can visualize the interface between the tectonic plates of the Pacific and Australia to understand what is going on underground. “said Dr Arnulf.
The scientists then used a supercomputer at the Texas Advanced Computing Center to look for patterns in the data. The results showed how weak the fault had become and where pressure was felt in the joints of the earth’s crust.
“The study allowed scientists to focus on the physical conditions of the fault where slow-slip events occur, providing an important test of a range of theories as to why they occur,” Dr. Wallace said. .
Dr Arnulf said that if scientists ignored slow-slip events, they risked miscalculating the amount of energy stored and released as tectonic plates move around the planet.
“They are an important part of the earthquake cycle because they occur in the same places as large magnitude earthquakes and slowly release tectonic energy over weeks or even months.”
He added that the Hikurangi subduction zone is ideal for studying slow-slip earthquakes, as they occur shallow enough to be imaged at high resolution using seismic techniques. This aspect had therefore attracted many international scientific agencies to New Zealand, bringing sophisticated technology and know-how to focus on our very active plate frontier.
The seismic data for the study was provided by GNS Science and the Ministry of Economic Development. The research was funded by UTIG and a grant from the Ministry of Business, Innovation and Employment fund to GNS Science.
SLIDE: The Hikurangi subduction zone which is 40 km from the east coast. Picture provided
COMPUTER: Dr Laura Wallace of GNS Science. Picture provided