Japan earthquake: Office rocked by 7.2 magnitude tremors

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The magnitude 7.9 earthquake struck on May 30, 2015, some 117 miles northwest of Chichijima in the Ogasawara Islands. At the time of the incident, the tremor’s epicentre was tracked to about 412 miles (664km) under the west Pacific Ocean. But according to a new study published by researchers from the University of Arizona, the earthquake was felt much deeper than previously thought.

The Arizona researchers analysed data collected by Japan’s network of seismometers to determine how deep the earthquake’s aftershocks travelled.

The earthquake’s most powerful quake, which peaked at magnitude 7.9 on the Richter scale, hit just off the coast of the remote Bonin Islands – a subtropical archipelago also known as the Ogasawara islands.

The islands sit some 6290 miles (997km) south of Tokyo and more mostly uninhabited, with the exception of Chichijima and Hahajima.

After the main earthquake jostled the region, the Arizona researchers found a series of aftershocks as deep as 467 miles (751km) underground.

Until now it was thought virtually impossible for earthquakes to strike this deep.

According to the US Geological Survey (USGS), earthquakes are typically recorded at depths between zero and 435 miles (zero and 700km).

Past these depths and the temperatures and pressures acting on the Earth’s rocks cause them to deform rather than break and fault.

But in the new study that was published in Geophysical Research Letters, the Arizona scientists appear to have found a new limit.

The study’s authors wrote: “The causes of earthquakes below depths of approximately 60km inside the Earth have been debated for nearly a century.

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“This study reports on the first detected earthquakes with source locations in the lower mantle.

“These observations provide new insights into the mechanisms that can produce earthquakes deep inside the Earth.”

However, according to a report in National Geographic, some scientists are being cautious about the study’s findings.

Before any definite conclusions are drawn from the findings, they believe more research needs to be done to confirm the aftershock did indeed strike this deep.

The lower mantle or mesosphere represents about 56 percent of the Earth’s total volume and is the liquid portion of the Earth’s mantle.

This layer below the planet’s surface extends from about 410 to 1,800 miles (660 to 2,900km) below the surface.

Under Japan, however, the lower mantle is believed to begin deeper, at about 435 miles (700km) down.

Japan sits within the Pacific Ring of Fire and is one of the world’s most seismically active regions.

The Ring of Fire, also known as the Circum-Pacific Belt, runs along the edge of the Pacific Ocean.

This region is characterised by frequent earthquakes and the highest concentration of active volcanoes in the world.

The USGS said: “Most earthquakes and volcanic eruptions do not strike randomly but occur in specific areas, such as along plate boundaries.

“One such area is the circum-Pacific Ring of Fire, where the Pacific Plate meets many surrounding tectonic plates.

“The Ring of Fire is the most seismically and volcanically active zone in the world.”

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