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On Earthquakes' Deep Origins



Scientists, technicians, and drill operators on board the Chikyu, a highly advanced scientific vessel.

The second campaign of the Nantroseize mission (short for Nankai Trough Seismogenic Zone Experiment) ended this February. Siegfried Lallemant from the Tectonics laboratory1 and his colleagues returned with a variety of rocks from active faults, and copious amounts of data.Launched by the international ocean drilling program IODP,2 this ambitious research program–which involves several CNRS laboratories–aims to take a closer look at the Nankai seismic fault. The fault, which runs along the oceanic trough of the same name off Japan’s Pacific coast between the Kii peninsula and the island of Shikoku, has caused some of the most devastating earthquakes known. The first phase of the project will last at least until 2011. The geophysicists who closely monitor the convulsions of the Earth’s crust are hoping to understand how earthquakes are triggered, like the one at the origin of the 2004 tsunami that took hundreds of thousands of lives in only a few seconds.
To ensure the success of the Nantroseize mission, the international community has acquired a new ship made in Japan, dubbed the Chikyu (“Earth,” in Japanese). “It is equipped with what’s called a drilling ‘riser,’ an outer casing that surrounds the drill pipe and injects mud whose density is controlled to counterbalance the high pressures found at great depths,” Lallemant explains. “This system makes it possible to drill–and to take measurements and rock samples–as far down as 6 to 7 kilometers below the ocean floor, all this of course under 2000 meters of water.” Scientists are expecting a great deal from the drilling program, planned to last over twelve months until the end of 2009. As well as taking rock samples to be meticulously examined in the lab, researchers have peppered the Nankai trough with sensors to monitor changes in physical parameters such as stress, deformation, and fluid pressure, and to spot possible warning signs of imminent earthquakes. All this is in the hope that one day, they’ll be able to predict earthquakes before they happen.

Azar Khalatbari

Notes :

1. Laboratoire de tectonique (CNRS / Université Paris-VI / Université Cergy-Pontoise).
2. Integrated Ocean Drilling Program. France joined the IODP program through the ECORD consortium (European Consortium for Ocean Research Drilling), which brings together 16 European partners and Canada.

Contacts :

Siegfried Lallemant
Laboratoire de tectonique, Cergy-Pontoise.


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