Powerful earthquakes in Japan can be caused by an underwater volcano located on a tectonic plate – scientists
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Several 7-magnitude earthquakes that have rocked Japan over the past 40 years may be caused by an extinct submarine volcano that lies on the tectonic plate off the coast of Japan and is breaking through the Earth’s mantle.
This is the conclusion reached by scientists at the Center for Earthquake Research and Information at the University of Memphis, writes Live Science.
An extinct submarine volcano known as the Daichi Kashima Seamount is located on the Pacific tectonic plate about 40 kilometers off the east coast of Japan.
Three tectonic plates intersect there: the Pacific plate in the east, the Philippine plate in the south, which sometimes fall under the Okhotsk plate in the north.
| Photo: NOAA Vents Program |
“The seamount is located on a section of the plate that began to sink into the Earth’s mantle between 150,000 and 250,000 years ago.” – said co-author of the study Yunseo Choi, associate professor at the Center for Earthquake Research and Information at the University of Memphis.
The seamount is located quite close to the surface, at a distance of 50 kilometers, and therefore can cause earthquakes, said the study’s lead author Sungho Lee, a doctoral student at the University of Memphis.
Although most of the seismic activity around it is small aftershocks, there have also been several earthquakes of magnitude 7 to 7.8 in 1982, 2008 and 201. Scientists could not explain them.
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| After the 2011 Tohoku earthquake. Photo: Yoshinori Kuwahara/Getty Images |
When a tectonic plate slides or sinks under another plate, the seamounts that pierce its surface scrape the bottom of the main plate. A 2008 study found that this friction is too weak to cause an earthquake, and can only cause small tremors.
But new data suggests the opposite, says Lee. Seismic information collected on the ocean floor in Japan indicates that seamounts face enormous resistance as they move along the submarine plate and sometimes get stuck.
“The seamount itself is almost stationary because it has very strong friction,” – says the scientist.
However, as the mountain sinks into the overhanging plate, stress builds up at its leading edge. The area around the seamount becomes blocked and stops. Scientists called this process a “hangover” event. The rest of the subducting plate continues its creeping descent into the Earth’s mantle.
“The stress builds up at the edge of the seamount, and after a while it propagates and migrates inward,” – claims the scientist.
This accretion cannot continue indefinitely, so the stress is released when the seamount suddenly breaks free from the overhanging plate and jerks forward. The underlying plate shakes in the opposite direction, causing a new type of earthquake that Lee and his colleagues call a hovering earthquake.
Read also: A newly formed volcanic island near Japan continues to grow. PHOTOS, VIDEOS
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