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Thinking while measuringSeptember 1, 2012

Hello, folks! We just turned at the corner of the halfway mark of our Expedition 337. The scientists are all busy at work in the lab, handling and processing the sediment samples that the CHIKYU has recovered by its drilling system. I’m, of course, one of them!

Every 12 hours of the night shift, I’m absorbed in measurements in the lab. What am I measuring? Maybe next time, I’ll tell you if I can have time to. In fact, I was very much looking forward to attending this CHIKYU expedition operating in this area off Shimokita, because the area is very attractive in a geological sense.

For the last few years, I have looked into geologic structure below the seafloor in this area, and, I’ve discovered the fact that huge submarine landslides have occurred repeatedly for the last few million years. This is an unbelievable fact! Because the seafloor here is very flat and spreads wide and almost horizontally, at less than 1 degree in gradient. Maybe, no one expects huge submarine landslides occurred in this area at first glance.

Using the latest seismic surveys, a number of submarine landslides have been identified one after another, all over the seven seas. And, they have come under scrutiny because they sometimes trigger tsunamis or cut off submarine cables, but, the pattern of submarine landslide is quite varied. The cause of ground instability under the sea still is poorly understood. On land, after a heavy rain, the ground water level can change. This sometimes makes the ground unstable and may lead to a landslide at a mountain slope.

On the other hand, how about the sub-seafloor? Seafloor sediments are all the time filled with water. I hope you understand the on-land system doesn’t simply work under the sea. And, the Shimokita area’s seafloor is almost horizontal.

Talking about geological background of the drill site at science meeting.

So, you might think it’s odd that I, who works to investigate submarine landslides, should attend this expedition, named “Deep coalbed biosphere”. It’s because characteristics of the geological formation in this area may be a key to approach this issue.

According to the structural analysis using seismic methods, the ground instability causing submarine landslides has proved to be related to natural gas, one of the major themes of our expedition. However, the gas is not thought to be large enough to be considered an available resource at this moment. And, landslides of this magnitude have not yet occurred during our lifetimes.

As one of my studies here, I’m trying to figure out past thermal conditions of the sediments. Temperature is very important parameter for status of gas and water in the geological formation, and for microbial activity as well. According to microbiological study, there might be a tremendously huge amount of microbial activity in this area. Microbes sometimes contribute to the process of natural gas formation. Thus, such an uncommon environment might be ultimately related to the ground instability leading to submarine landslides, shouldn’t it? Considering such speculation, I am absorbed in the lab measurements tonight as well...

Working on multi-sensor core logger (MSCL: right behind) with Mr.Takahiro Suzuki (front),
one of the excellent lab technicians.

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