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New research helps explain “silent earthquake” in New Zealand’s North Island

New research helps explain “silent earthquake” in New Zealand’s North Island

Seamounts provide clues to solve structural problems

An electromagnetic sensor is heading to the sea floor to collect data. Photo: Summer Naif/ Electromagnetic Geophysics Laboratory

The edge of Hikurangi on the east coast of New Zealand’s North Island is where the Pacific tectonic plate dives beneath the Australian tectonic plate, which scientists call a subduction zone. This interface between tectonic plates is part of the reason why more than 15,000 earthquakes occur in the region each year. Most are too small to be noticed, but between 150 and 200 are big enough to be felt. Geological evidence indicates that before the start of human records, major earthquakes occurred in the southern edge of the border.

Christine Chesley

Lead author Christine Chesley is a graduate student at Columbia University’s Lamont-Dougherty Earth Observatory. Photo: Kerry Key

Geophysicists, geologists and geochemists from all over the world have been working together to understand why this plate boundary produces such behavior, producing both imperceptible silent earthquakes and potentially major earthquakes.A kind Research published in the journal today natural Provides new perspectives and possible answers.

Scientists know that on the ocean floor in the northern part of the island, plates sliding together slowly will produce small, slow-moving earthquakes called Slow slip event-Actions that take weeks, sometimes months, to complete. But at the southern end of the island, the tectonic plates did not slide slowly as in the north, but locked. This locking creates conditions for the sudden release of the plate, which may trigger a major earthquake.

Marine electromagnetic geophysicist said: “This is really weird, and I don’t understand why in a relatively small geographic area, you will go from many small, slow-moving earthquakes to the possibility of real big earthquakes.” Christine Chesley, A graduate student at Columbia University’s Lamont-Dougherty Earth Observatory and the lead author of a new paper. “This is what we have been trying to understand, this difference in profit margins.”

In December 2018, a research team began a 29-day deep-sea cruise to collect data. Similar to MRI imaging of the earth, the team uses electromagnetic wave energy to measure how currents pass through features on the seafloor. From these data, the team can more accurately understand the role of seamounts and large submarine mountains in generating earthquakes.

Location map of the sensor along the groove

Hikurangi subduction zone map and the location where electromagnetic receivers are deployed to collect data.Source: Christine Chesley, used Geographic map application And the data comes from Ryan et al. (2009)

“There are large seamounts on the northern edge. It is not clear what these mountains will do when they subduct (dive into the depths of the earth), and how this dynamic affects the interaction between the two plates,” Chesley said.

It turns out that seamounts contain much more water than geophysicists expected-about three to five times that of a typical oceanic crust. The abundance of water lubricates the plates where they connect, helps smooth any sliding, and prevents the plates from sticking, which can trigger a major earthquake. This helps explain the trend of slow and silent earthquakes at the northern end of the edge.

Using these data, Chesley and her colleagues were also able to carefully examine the occurrence of seamount subduction. They found an area in the upper plate that appeared to be destroyed by subducting seamounts. This upper plate area also seems to have more water.

Chesley said: “This shows that the seamount is destroying the upper plate and weakening it, which helps explain the anomalous patterns of silent earthquakes there.” This example provides another indication of how seamounts affect tectonic behavior and earthquake disasters.

Conversely, the lack of lubrication and the weakening of seamounts may make the southern part of the island more prone to adhesions and major earthquakes.

Chesley, she is expected to complete her PhD. In the fall, it is hoped that these findings will encourage researchers to consider how the water in these seamounts contributes to seismic behavior as they continue to work to understand slow-moving earthquakes. Chesley said: “The more we study earthquakes, it seems that water plays a leading role in regulating fault slip.” “Knowing when and where to put water into the system can only improve natural disaster assessment.”

Samer Naif, former Lamont Assistant Research Professor and current Assistant Professor at Georgia Institute of Technology; Kerry Key, Associate Professor at Lamont-Dougherty Earth Observatory; and Dan Bassett, a research scientist at GNS Science, collaborated on this research. The project was funded by the National Science Foundation.

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