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Impact of Magnitude 9 Earthquake in Japan Still Felt Today

Researchers combed through 10 years of seismic data from the volatile Japan Trench in order to better understand the threat posed by a fault which triggered the deadly 2011 Tohoku-oki quake.

(CN) --- A magnitude 9 earthquake that struck Japan’s Tohoku coast in 2011 and triggered a deadly tsunami that devastated the region left a wake of devastation and disorder that is still evident today, according to a study released Thursday examining years of earthquake data.

The Tohoku-Oki earthquake struck Japan on March 11, 2011, and is the largest megathrust tremor ever recorded in the nation.

The quake and the resulting 124-foot tsunami --- one of the largest recorded in geological history --- caused nearly $160 billion in damage and left communities reeling and unable to fully recover even a decade later.

Even now, the quake threatens the global environment after it crippled the now infamous Fukushima nuclear power plant.

The National Police Agency of Japan recorded an estimated 18,500 people dead or missing after the massive earthquake and tsunami.

Japan's Tohoku coast is no stranger to earthquakes. One of the most seismically active in the nation, the region has experienced its share over decades of powerful, tsunami-producing earthquakes.

However, the 2011 Tohoku-oki earthquake was the first tremor to be comprehensively recorded by a complex network of seismic instruments plotted across the Japan Trench.

The trench area --- a highly volatile zone located off the northeast coast of the main island of Japan --- has frequent seismic activity due to plate tectonics.  

In the trench area, massive amounts of pressure caused the Pacific Plate to dip below the Okhotsk Plate, leading to intense abrasion that shakes the earth.

The 2011 Tohoku-oki earthquake was triggered when the area where the two plates converge --- known as a coseismic fault slip --- unexpectedly ruptured into a deep section of the fault.

Researchers at the Japan Agency for Marine-Earth Science and Technology in Yokohama sought to examine the past decade of data collected along the trench area in order to better understand the impact of the 2011 quake.

Lead study author Shuichi Kodaira and colleagues relied on a deep-sea drilling project to collect soil samples from the plate boundary. 

Analyses of the sample revealed critical failures of the plate structure and weakness in the faults soil composition, according to the study published Thursday in the journal Science

“This showed that the plate boundary fault is rich in weak layers of clay and suggested that thermal pressurization within the clay layers promoted the exceptionally large coseismic fault slip,” the study said.

Researchers said that the findings show the probability of another major earthquake striking the region is relatively low, according to the study titled "Investigating a tsunamigenic megathrust earthquake in the Japan Trench."

However, continued seismic activity in shallow section of the Japan Trench and structural weaknesses in the plate mean earthquakes and resulting tsunamis will continue to be a threat for the Tohoku region.

“Viscoelastic relaxation is predominant in the central part of the trench, where the large coseismic slip extended to the trench,” the study authors wrote. “The relaxation displaces this seafloor westward, whereas afterslip displaces it eastward around the main rupture zone. These observations, along with aftershock activity from normal fault earthquakes in the incoming oceanic plate, indicate that trench-normal extension remains in the oceanic plate and seaward of the main rupture zone.”

Researchers did not immediately respond to a request for further comment on the study by press time.

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