CDEX Web Magazine 地球発見

CDEX
For the Future:Scientific Research on what have actually happened since the Earthquake and Tsunami

The CHIKYU has added a new mission to her previously planned drilling projects for 2012, in order to study the focal area of the 2011 Earthquake off the Pacific Coast of Tohoku. This will make 2012 an especially busy year for her. Wataru Azuma, Director-General of the Center for Deep Earth Exploration (CDEX), tells us about the details.
(Published in April 2012)

Wataru Azuma, Director-General of the Center for Deep Earth Exploration (CDEX) Interviewee:
Wataru Azuma
Director-General of the Center for Deep Earth Exploration (CDEX)

A Year Since the Great East Japan Earthquake Disaster

 On March 11 last year, the CHIKYU was berthed in the Port of Hachinohe in Aomori Prefecture. The CHIKYU was damaged by the tsunami when it hit the harbor, losing one of the rear azimuth thrusters on the port side of the ship. The ship’s hull was also partially damaged. However, all crew and a group of schoolchildren onboard for a field trip escaped unharmed. The scale of the damage was thus relatively minor. However, the ship’s schedule suffered serious disruption as a result. It was impossible to carry out technically challenging scientific drilling with a missing thruster. As a result, a research expedition to study the deep coal bed biosphere off Shimokita, northern Honshu, scheduled to start on March 15, had to be postponed.

 After repairs were made to the damaged hull, the CHIKYU left for a resource drilling project off the coast of Sri Lanka at the end of 2011. With calm and favorable weather conditions, the cruise was successfully completed without any problem with the remaining five thrusters. The essential purpose of the CHIKYU is scientific drilling, but drilling for resources is another way in which the ship can make a contribution to society. Compared with the particularities of scientific drilling, more general resource drilling work was thought to be a good way to reconfirm basic drilling techniques in operations and engineering.

What’s next ? — “The Japan Trench Fast Drilling Project”

 One of the distinguishing features of the Great East Japan Earthquake Disaster was the size of the tsunami generated. In normal ocean trench earthquakes, the fault slip is largest in the focal area deep beneath the seafloor and smaller closer to the surface. In this earthquake, there was substantial movement in shallow regions, and it was this that caused the tsunami. Research carried out to date has shown seafloor movement of as much as 50m horizontally and 10m vertically near the trench axis.

 This project will therefore involve two drilling missions close to the trench axis. One mission will measure temperature. The aim is to calculate the amount of energy corresponding to the size of the fault slip that generated the earthquake, and thus understand the conditions in the vicinity at the time when the earthquake occurred. The other mission will collect core samples. Frictional resistance at the point of major movement in shallow regions is believed to have been small. Accordingly, we will use the samples to reproduce the conditions in the laboratory, in order to elucidate the mechanism of the fault slip that caused the huge earthquake.

 Improving our understanding of the tsunami in particular will help to prevent future disasters, and we believe that this project is of considerable significance to society. This will also be the first time that measurements of temperature and other factors have ever been made after a magnitude 9.0 level earthquake. This has attracted considerable attention from different parts of the world. We are confident that the results of this expedition, the first of its kind, will contribute to global scientific progress.

 Of course, previously scheduled expeditions will also go ahead as planned. After the Expedition of Japan Trench Fast Drilling Project (JFAST) is completed, a new thruster will be installed and we will prepare to conduct another study off the coast of Hachinohe on the Shimokita Peninsula. The expedition will collect samples from a depth of 2,111m below the seafloor, a world record in scientific ocean drilling. We will aim to gain a better understanding of the carbon circulation system, including methane hydrate, and study the potential for carbon dioxide collection and sequestration technology in sub-seafloor geological layers. After that we will work on the ongoing project of Nankai Trough Seismogenic Zone Experiment.

 2012 will be a very busy year for CHIKYU, in which we proceed press forward with our efforts to best contribute our scientific roles to the society, working together to ensure safety as our priority during our survey and research. We look forward to sharing the results of CHIKYU’s work with you soon.

Wataru Azuma, Director-General of the Center for Deep Earth Exploration (CDEX)