I use the Tokyo Metro subway system for my daily commute to the office, and I was recently impressed with the message on a poster in the metro station. The poster commemorates the 90th operations anniversary of the subway (1927-2017), saying "Underground is the future, now and in the future".
This yellow poster was designed with a motif based on the Ginza Line, the first subway in Japan, and is an astonishing poster in poorly lighted station. The year 1927 is just four years after the Great Kanto Earthquake (1923), and that earth scientists and engineers may have an image of the future while still in the midst of reconstructing the Tokyo metropolis. In these circumstances, launching subway operations may give some great hope to the citizens of Tokyo and Japan.
At noon on 1 September 1923, a magnitude 8 earthquake struck the Kanto region. My grandmother told me stories when I was a child, of how she remembered that while preparing lunch, she felt hard shaking and jumped out of the house, where she saw the ground cracking. This earthquake, based on our current understanding, was caused by plate motion between the Philippine Sea and the Eurasian plates (or the North American plate). The plate boundary fault earthquake rocked the region from Sagami Bay to the Tokyo bay mouth and Boso Peninsula. This process of deformation on the earthquake fault plane helped clarify and elucidate the mechanism of the Kanto earthquake, and this understanding is still being advanced by many researchers. This research was very assisted by the existence of so many useful earthquake records from various places all over Japan. This is an immensely great treasure of scientifically monitored, recorded, and well-described data in Japan.
Chikyu has been advancing IODP scientific drilling since 2007. Chikyu has especially focused on researching subduction-type large earthquakes in the Nankai Trough and the Japan Trench. Some very important and widely recognized scientific results have already been published in many leading scientific journals, and are helping to rewrite geology textbooks. Previous scientific thought did not believe that, the so-called a-seismic zone, in the Nankai region is where seismic slippage with significantly high slip velocity is caused, accompanied by large crustal deformation and tsunamis. The new findings from the IODP expeditions of Chikyu not only show that this is really the case, but also recent real-time data streams from the IODP Nankai Trough borehole monitoring systems reveal that slow earthquakes are frequently initiated and “jump-started” by a relatively large and nearby earthquake. It has been about 70 years since the last time the plate boundary fault slipped during the Tonankai earthquake in 1944; however, the amount of slip for each of these slow earthquakes is extremely small (about 1 - 2 cm), and it was only because of these sub-seafloor observatories that these data were recorded it, which led to this great discovery. These observatories now make it possible to monitor the process/evolution from a slow to large earthquakes, and this is likely the beginning of a new field of earthquake research.
The general scale movement of the earth’s interior is very slow compared to that of our daily lives. However, the level of precision in monitoring the movements of the Earth, even such a small scale of dislocation of crust, seem to now make this possible. The subway was born from the idea of effectively and creatively utilizing underground space, and modern convenience and safety has been constructed based on such ideas. Similarly, underground borehole monitoring has the great potential to contribute to the construction of a safe and secure society through high-resolution observation and monitoring the Earth.
Indeed, "underground is the future." We in JAMSTEC are preparing the next stage of scientific drilling in the Nankai Trough in 2018, setting out to accomplish a new level of historic ultra-deep scientific drilling. Through our scientific and engineering challenges, Chikyu looks to contribute positively to our future.