The Center for Deep Earth Exploration’s scientific Drilling Vessel Chikyu is the vessel that introduced riser drilling technology to scientific research for the first time. Riser drilling allows for ultra-deep drilling below the seabed. Chikyu has the equipment and tools aboard, needed to drill deeper into the Earth than any previous scientific drilling vessel. Currently, even onshore drilling can sample relic mantle rocks, so that direct sampling of the mantle via Chikyu’s cutting-edge research facilities can now be said to be coming within reach.
As the International Ocean Discovery Program’s (IODP) Japanese ship, Chikyu looks to provide top-class research into the Earth’s past, present, and future. and be a leading contributor to advancing human scientific knowledge.
Investigating the ‘Whys’ of Great Earthquakes
Of primary importance is protecting the lives of those people living in areas exposed to great earthquakes and tsunamis. In part, Chikyu was built to investigate the mechanisms behind these terrible events, and help us to better understand and therefore mitigate their effects of these natural disasters.
The Nankai Trough off the Kii Peninsula is one such “source region” of the extremely destructive 1944 Tonankai Earthquake. In fact, huge earthquakes occur here repeatedly at intervals of about 90-150 years. Chikyu continues drilling in the Nankai Trough, having reached a science record depth of just over 3000. During the 2011 JFAST expedition (IODP Exp 343 & 343T), drilling in water depth of about 6,900 m to about 850 m below the seabed was performed drilling 5 holes to sample of the plate boundary fault (earthquake fault) and successfully deployed a borehole monitoring system measuring temperature and pressure.
Some of the scientific findings that came out of these expeditions was that earthquake slip could propagate from the hypocenter all the way to the trench at the front of the accretionary prism. Previously, it was thought that this was not possible. These are only part of the support that ultra-deep water, deep drilling, and riser technology, operating in harsh conditions and in areas with very strong ocean currents JAMSTEC and CDEX provide aboard Chikyu.
The Origin of Life
Life on the primitive Earth first began in a high temperature, high pressure, and anoxic environment. Presently, the only places where these conditions exist are deep underground, in hot springs, and deep sea hydrothermal vents. Exploration by Chikyu in deep sub seafloor coalbeds has found assemblages of microbes that have adapted to their environment as it was slowly buried and turned to coal, over millions of years.
These microbes have remained while life on the surface or in the ocean evolved and changed, leaving these assemblages phylogenetically diverged, while much of the genetic material within them are new to science, and not included in any genetic databases.
An important development in this research, are newly developed sample collecting tools that maintain the in situ pressure. Compared to the busy beat of our daily lives, research into, and new developments of, the extremely slow-living sub seafloor life can be expected to reveal new applications of that new knowledge.
Quest for the Mantle
Mantle drilling is a plan to drill into the currently unexplored mantle of the Earth, through the oceanic crust. This was one of the driving forces for developing and launching the Scientific Drillship Chikyu.
The Earth has been changing its appearance, due to continental drift and volcanic activity, ever since its creation. The driving force behind this is believed to be the mantle, a strange “flowing solid”. By investigating the mantle, we can clarify how it can effect change on the Earth’s surface.
Mantle drilling has not been achieved in the more than 50 years since it was first proposed. The scientific targets have also changed and evolved, as “relict mantle” material has been collected, and the fundamental understanding of the mantle itself, has changed.
Ocean floor studies involving drilling have shown that the tectonic plates making up the Earth's surface are not the same. While the structure and composition of the different plates vary from place to place, we still don’t fully understand the global significance of these differences. It is believed that these are closely related to life and the environmental issues.
Chikyu has the capability to reach the mantle, through direct drilling, and collect samples to clarify the essence of the oceanic plate. To do this requires new techniques to drill out 7,000 meters below the seafloor, in regions where ambient temperatures can reach 250 degrees C. Establishment this is a very challenging task, but has the potential of creating many new technological advancements, tools, and techniques for Japan.
Cores: History Books of the Earth’s Past
Geological samples (core) from formations drilled by Chikyu are a valuable record of past global environmental changes.
For example, researchers aboard Chikyu discovered traces of past earthquakes in core samples. It’s expected that these can shed light on past earthquakes and allow for better earthquake mitigation.
To date, Chikyu has collected more than 1,000 cores with a total core recovery length of several kilometers. These cores provide invaluable data regarding past changes and fluctuations in sea level, sea temperature, geomagnetic fields, atmospheric temperature, and more. Careful analysis will reveal the history of the Earth, and provides clues about the future.