Earthquakes in Japan and South America: The Week’s Major Tremors Trace the Pacific Rim


Home / Earthquakes in Japan and South America: The Week’s Major Tremors Trace the Pacific Rim

The Japanese Earthquake Cluster

Japan tectonic setting

Japan is located where four of the earth’s tectonic plates meet – Image courtesy USGS

On the other side of the Pacific Ocean, a cluster of 14 earthquakes greater than, or equal to, M4 occurred along the subduction zone where the Pacific Plate is forced beneath the Okhotsk microplate (described by Rhea et al as “a proposed subdivision of the North America plate”) to the north of the quadruple junction between the  Okhotsk, Pacific, Philippine and Eurasian plates.

The presence of this junction makes the tectonic setting of Japan, close to which it lies, highly unstable: the area is, according to the USGS, “geologically complex and produce numerous earthquakes from multiple sources.”

The area is notable as the location of some of the earth’s greatest and most devastating earthquakes, most recently the Tohuko earthquake of 2011 (off the island of Honshu), one of the largest on record at M9.0.

Several Significant Quakes This Week

With several significant earthquakes, the week showed activity along most of the planet’s major subduction zones – other significant tremors included an M6.4 off the Aleutian Islands in the far north of the Pacific and an M6.0 in the Solomon Islands. Activity also continued along the subduction zone of the Tonga Trench.


Rhea, S. et al. Seismicity of the Earth 1900—2007, Japan and Vicinity. (2010). USGS. Accessed October 2, 2012.

USGS. Real Time Earthquake Map. (2012).  Accessed October 2, 2012.

USGS. M7.3 – 9km WNW of San Agustin, Colombia. (2012).  Accessed October 2, 2012.

USGS. Seismotectonics of Japan and Vicinity. (2012).  Accessed October 2, 2012.

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