The Tohoku earthquake occurred off the east coast of Japan on March 3, 2011. It is considered the most severe quake since records began in Japan. More than 22,000 people lost their lives and 400,000 buildings partially or completely collapsed. The tsunami triggered by the seaquake led to the nuclear disaster at Fukushima.
Dr. Piero Bellanova is a research associate at the Institute of Neotectonics and Georisks. Since the beginning of September, he has swapped his office on Lochnerstrasse in Aachen for the Japanese research drilling vessel "Chikyu". Until December 20, he is part of an international research team that is investigating the causes of the great Tohoku earthquake of 2011 through deep-sea drilling.
Marked change at the plate boundary
Just getting on board was a great adventure for the Aachen scientist: "We jumped out of the helicopter onto the deck and got straight to work," says Bellanova. This is the second expedition to this region. Just 13 months after the major 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 marked 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.
The aim of the current IODP Expedition 405 is to determine the properties, processes and conditions within the subduction zones, twelve years after the first IODP expedition to the Japan Trench. These promote strong sliding in the trenches and can contribute to the formation of large tsunamis. During the expedition, physical data will be recorded from the boreholes, cores will be obtained and analyzed on board the Chikyu and observatories will be installed.
Not all of the researchers will live and work on the Chikyu for the entire four months; the expedition is divided into two sections. The researchers have a defined role on board in the so-called core flow and in the upcoming investigations and analyses. Dr. Piero Bellanova is part of the sedimentologist/lithology team that will describe the appearance of the cores, identify sediment structures and faults, and analyze samples to determine sediment composition and lithology.
As is usual with IODP expeditions, the drill cores are analyzed 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 want to answer using the samples and data obtained. Dr. Bellanova’s post-expedition research will focus on identifying past earthquake events similar to the 2011 Tohoku-oki earthquake. To this end, numerous samples were taken to characterize and better understand paleoseismic event locations, such as turbidites and so-called ’homogenites’, using sedimentological and biogeochemical analysis methods at RWTH Aachen University. This allows a better understanding of the paleoseismic activity of the Japan Trench and an improvement of the protective measures.
The research vessel is currently off the east coast of Japan at the height of Fukushima. "We have now described almost a kilometer of drill cores and have already learned so much," says Bellanova, describing the day-to-day research on board, "it is unique and fascinating to get a view through the accretionary wedge and through the plate boundary of the subduction zone and to record the sediment archives full of seismic event locations, faults and mass transports."
Background information on the expedition The expedition is being organized 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. Expedition website: https://www.jamstec.go.jp/chikyu/e/exp405/index.html
The expedition should be able to answer the following scientific questions:
- the stress and strain conditions within and around the fault zone and their spatial and temporal variation
- the geology of the subsurface, including the physical rock properties that influence the slip behavior and location of the faults, as well as the geological record of past earthquakes and tsunamis
- the hydrogeology of the fault zone - including the hydrogeological structure of faults, fractures and permeable zones at the plate boundary and their influence on effective stress and earthquake mechanics as well as the temporal variation of conditions.
