Honshu: The Physical Make-Up of Japan's Largest Island: September 2012

Honshu began its rise some 60 million years ago with the collision of the Eurasian Plate with that of the North American Plate (http://www.glgarcs.net/intro/history_p4.html) and lasted for 37 million years. This was the groundwork for Honshu's construction.

The convergence of the Pacific Plate towards the Eurasian Plate

The two plates converged on one another, with the North American plate subducting beneath the Eurasian. As the North American plate slid beneath the Eurasian, the North American plate underwent intense heat and pressure changes, becoming magma, which eventually escaped through either seeping through weakened rock or exploding out of magma chambers (volcanoes). As this magma shot out, it solidified, and with the continual volcanic activity over millions of years, formed new layers again and again. This is how northern Honshu eventually came to be (http://geology.com/nsta/convergent-plate-boundaries.shtml) (http://www.glgarcs.net/intro/history_p5.html). The Southern portion of Honshu was formed in the same manner, except it was that of the Philippine Sea Plate subducting beneath the Eurasian (http://www.episodes.co.in/www/backissues/143/articles--190.pdf).

File:Tectonic map of southwest Japan.png

The MTL depicted in red

Because of its violent history, many active fault lines run through Honshu. Its most famous and active is the Japanese Median Tectonic Line (MTL). Due to length and varying degrees of strain by the converging plates, the MTL provides different types of stress on Honshu. Southwest Honshu typically experiences strike-slip strain, while Northern Honshu experiences compression strain (http://www.numo.or.jp/en/reports/pdf/Level3_SF_Final-06.pdf). These different types of fault activity produce many deadly earthquakes, like the one experienced in Kobe, Japan in 1995, which killed over 6,000 people and upwards of 42,000 wounded (http://www.nsm.buffalo.edu/courses/gly433/pdfPowerPoint/Laity.pdf) (http://www.drj.com/article-archives/earthquakes/the-great-hanshin-earthquake.html). Because of the sheer number of fault lines running through Honshu, earthquakes are a common occurrence.