On the trail of the 2011 mega earthquake

MARUM - Center for Marine Environmental Sciences, University of Bremen

 

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The scientific drilling vessel CHIKYU.

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Credit: Photo: JAMSTEC

Since the beginning of September and until December 20 of this year, a team of international researchers has been underway on the Japanese research drilling vessel CHIKYU to get to the bottom of the causes of the great Tōhoku earthquake of 2011 through deep-sea drilling.

It is the second expedition to this region. Just 13 months after the earthquake, during the IODP Expedition 343 “Japan Trench Fast Drilling Project” (JFAST) in 2012, the researchers drilled through the plate boundary. The recovered core showed a striking change at the plate boundary, a subduction zone where the Pacific Plate is subducting beneath the Eurasian Plate. An installed temperature observatory showed a signature of frictional heat from the earthquake.

Twelve years after the first IODP expedition to the Japan Trench, the aim of IODP Expedition 405 is now to determine the properties, processes and conditions within the subduction zones – and how these have changed since JFAST. These promote strong sliding in the trenches and can contribute to the formation of large tsunamis. During the expedition, physical data from the boreholes will be recorded, cores will be taken and analyzed on board the CHIKYU and observatories will be installed.

The researchers are split into two teams, each living and working on the CHIKYU for about two months. Each scientist has a defined role on board in the so-called core flow and in the upcoming investigations and analyses. In the first half of the expedition, Dr. Matt Ikari from MARUM was on board as team leader for the physical properties’ specialists. His team is concerned with the geophysical measurement of drill core samples. This includes water content, porosity, thermal conductivity, elastic wave speed and shear strength.

MARUM scientist Dr. Junli Zhang is currently on board the CHIKYU on the second leg of the journey. He is part of the geochemistry team, which takes samples, carries out geochemical measurements, analyzes data and contributes to the reports, as do all the researchers on board. 

As is usual with IODP expeditions, the drill cores are analyzed and sampled according to defined standards, and the same applies to the data, which is then made available to all expedition participants and later to the entire scientific community.

In addition, the researchers pursue their own research questions, which they also want to answer using the samples and data obtained. “After the expedition, in collaboration with other science party members and a few external partners, I plan to make geotechnical laboratory measurements on the recovered cores, with an important aspect being the preservation of the condition of the recovered rock/sediment to be as it was in the earth.  That way, we can get a far more accurate view of how faults which produce huge earthquakes actually move,” explains Matt Ikari.

Junli Zhang will focus on pore pressure and fluid flow processes in the subduction zone of the Japan Trench, as well as interactions between water and rock, in his post-cruise research. Speaking about his experience on the CHIKYU so far, he shared, “The expedition has been going very smoothly. When I got on the ship, we were continuing with the drilling operations. In the first few days, I went through a quick handover and received intensive training on core flow, sampling methods, and geochemical measurements, among other things. This was very helpful and allowed me to quickly settle into my duties.”

 

Background information on the expedition:

The expedition is conducted by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). It involves 56 scientists from ten countries who will work on board the CHIKYU in two expedition phases.

The expedition aims to answer the following scientific questions:

(1) The current state of stress accumulation around the fault zone after more than ten years after the earthquake.
(2) The structure of the fault that caused the earthquake, its physical characteristics, and the factors that control the slip behavior.
(3) The effects of fluids on the stress state around the fault zone.

Matt Ikari (Physical Property, right), Hiroki Sone (Structure geology) are working on whole round core sampling.

Credit

Photo: JAMSTEC/IODP

More information:

• Expedition website: https://www.jamstec.go.jp/chikyu/e/exp405/index.html and background: https://youtu.be/noEBFf2x7xU 
• JAMSTEC press release: https://www.jamstec.go.jp/e/about/press_release/20240829_2/
• Article on the expedition in “Japan Forward”: https://japan-forward.com/aboard-the-chikyu-searching-for-new-earthquake-clues-deep-in-the-japan-trench/
• Information on the J-FAST expedition: https://www.jamstec.go.jp/chikyu/e/exp343/expedition.html
• Press release of the MARUM expedition to the Japan Trench 2012: https://www.marum.de/en/Uncovering-the-Traces-of-the-Great-Tohoku-Earthquake.html

MARUM produces fundamental scientific knowledge about the role of the ocean and the seafloor in the total Earth system. The dynamics of the oceans and the seabed significantly impact the entire Earth system through the interaction of geological, physical, biological and chemical processes. These influence both the climate and the global carbon cycle, resulting in the creation of unique biological systems. MARUM is committed to fundamental and unbiased research in the interests of society, the marine environment, and in accordance with the sustainability goals of the United Nations. It publishes its quality-assured scientific data to make it publicly available. MARUM informs the public about new discoveries in the marine environment and provides practical knowledge through its dialogue with society. MARUM cooperation with companies and industrial partners is carried out in accordance with its goal of protecting the marine environment.