Core samples from subsea fault system off Japan, might shed light on earthquake generation

An International team of scientists aboard the drilling vessel Chikyu, have obtained core samples from a subea fault system in Nankai Trough, a region off the Pacific coast of Japan, which have provided new data source on how earthquakes are generated.

Washington, Feb 6 : An International team of scientists aboard the drilling vessel Chikyu, have obtained core samples from a subea fault system in Nankai Trough, a region off the Pacific coast of Japan, which have provided new data source on how earthquakes are generated.

Part of the third expedition of the Integrated Ocean Drilling Program's Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), the aim of the research team is to evaluate the deformation, structural partitioning, and physical characteristics of the Nankai Trough fault zone.

Led by co-chief scientists Elizabeth Screaton of University of Florida, and Gaku Kimura of University of Tokyo, this expedition successfully drilled and cored 13 boreholes in the fault zone.

"We collected more than 5,000 samples from the cores for further examination," said Dr. Screaton. "The resulting data will provide important new constraints on models of the evolution of the subduction zone and its relationship to earthquake and tsunami generation," he added.

The Nankai Trough, a geological trench approximately 770 kilometers long, stretches from the Suruga Bay to where the Philippine Sea Plate slips (subducts) under southwest Japan. Along this subduction zone, sediment on the underlying tectonic plate continuously scrapes off and adds material to the overriding plate, forming new geological sediments called the accretionary prism.

"Understanding the deformation within the accretionary prism and its fault zones is an important factor in understanding how earthquakes are generated and why some earthquakes cause disturbance at the seafloor that leads to tsunamis," explained Screaton.

Expedition scientists examined the sediments ranging from the youngest on the slope overlying the accretionary prism, through fault zones and into sediments underneath the megasplay fault and frontal thrust.

Megasplay refers to large faults that branch off the major plate boundary, to near the seafloor.

According to Dr. Kimura, even the youngest sediments have an important story to tell.

"The sediments provide information about past slope failures, which may relate to past megasplay movement and earthquakes, and which may cause tsunamis," said Kimura.

ANI