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Distorted ocean plates caused complex earthquakes off East Cape, New Zealand

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The subduction zone, where the slabs of the ocean plate are pushed under another tectonic plate and subduct into the mantle, causes the world’s largest and most devastating earthquakes. Reconstructing the shape and stress conditions of the subducted slab in the subduction zone is important for understanding and preparing for a major earthquake. However, this is difficult because the depth of these slabs is so great. Seismologists rely primarily on the rare windows to these deeply buried slabs provided by the rare but strong earthquakes that occur within the slab (called intraslab earthquakes).

In a new study published in Geophysics Research Letter Used by a research team led by the University of Tsukuba Earthquake data It was generated by a magnitude 7.3 earthquake on March 4, 2021 at the northeastern tip of the North Island of New Zealand and was detected by seismographs around the world. This is to investigate the particularly unusual shape and stress conditions of subducted slabs under the surface of the region in this area. ..

“The 2021 East Cape Earthquake exhibited a complex destruction process because it is located on the border between the Kermadec Trench in the north and the Hikrangi Margin in the south,” explains Assistant Professor Ryo Okuwaki, the lead author of the study. .. “To investigate the shape of the stress field and the seismic rupture process, we used a new finite fault reversal technique that does not require existing knowledge of faults in the area.”

This study revealed multiple episodes of rupture produced by both underground compression and elongation at varying depths. These episodes included a shallow (~ 30 km) rupture due to an extension perpendicular to the trench, as would normally be expected in a subduction zone. However, unexpectedly, a deep (~ 70 km) rupture occurred with compression parallel to the subduction trench.

“Two alternative or interrelated factors may explain what is unique. rupture The lead author, Professor Yuji Yagi, describes the shape of the 2021 East Cape earthquake. Second, the transition from the Kermadec Trench to the Hikrangi Margin, where the subducting oceanic crust is fairly thick, can create local conditions that cause anomalous fault patterns. “

Due to the rarity of deep earthquakes in the slab in this region, it is currently difficult to distinguish between these two possibilities, and in fact both factors in creating the complex stress fields revealed by East Cape. Can play an important role. earthquake .. Further earthquakes off the northeast coast of New Zealand in the future could shed more light on the mystery of this deep crustal movement.

For more information:
Ryo Okuwaki et al., New Zealand Earthquake, illuminating slabs distorted by the evolution of complex intra-slab bursts at Mw 7.3 East Cape in 2021 Geophysics Research Letter (2021). DOI: 10.1029 / 2021GL095117

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University of Tsukuba

Quote : A distorted ocean plate caused a complex earthquake off the coast of East Cape, New Zealand (27 December 2021) 27 December 2021 https://phys.org/news/2021-12-contorted-oceanic- Obtained from plate-complex-quake.html

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