Ocean-drilling expedition cites new evidence related to origin and evolution of quakes

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Washington, August 18 (ANI): An ocean-drilling expedition in Japan has come across new evidence related to the origin and evolution of earthquakes.

The expedition is being conducted as part of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), which is long-term scientific ocean-drilling project conducted by the Integrated Ocean Drilling Program (IODP).

Since September 2007, rotating teams of scientists have spent months aboard Japan's drilling vessel, CHIKYU, investigating the Nankai Trough, a seismogenic zone located beneath the ocean off the southwest coast of Japan.

Drilling operations, managed by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) through its Center for Deep Earth Exploration, have resulted in a collection of cored samples from the sea floor, which have provided scientists with deeper insights into the geologic past of the area.

This area is one of the most active earthquake zones on the planet. While being subducted, sediments are scraped off the oceanic plate and added to the overriding continental plate.

Due to the movement of the plates, these so-called accretionary wedges are exposed to enormous stress that form large faults.

The landward wedge in the Nankai Trough is completely intersected by such a prominent fault which extends laterally over more than 120 km.

Scientists refer to this structure as "the megasplay."

Movements along such megasplay faults during large magnitude earthquakes generated at depth may rupture the ocean floor and generate tsunamis.

"Our knowledge of megasplay faults up till now has been based on seismic or modelling experiments accomplished over the last twenty years," said Michael Strasser, a Post-Doc Fellow of the Center for Marine Environmental Sciences (MARUM) at University of Bremen.

"For the first time, with cored samples brought onto the CHIKYU, it has become possible to reconstruct the geological history of a fault in great detail," he added.

With his associates, Dr. Strasser found that the fault in the Nankai Trough originated about two million years ago.

From the information recorded in the cores, the research team can draw conclusions on the mechanics of the accretionary wedge.

They also can infer in which geological time periods the fault was most active.

According to Strasser, after an initial period of high activity, the movement along the fault slowed down. Since about 1.55 million years ago, this fault has been reactivated, favoring ongoing megasplay slip along it.

"Ultimately, we hope to detect signals occurring just before an earthquake to get a better understanding of the processes leading to earthquakes and tsunamis," Strasser explained. (ANI)

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