Median Tectonic Line, Japan

The Median Tectonic Line is Japan's longest fault system, running from near Ibaraki Prefecture, where it connects with the Itoigawa-Shizuoka Tectonic Line and the Fossa Magna, parallel to Japan's volcanic arc across central Honshu toward Nagoya, crossing Mikawa Bay and the Inland Sea through several straits before continuing through Shikoku and into Kyushu. It marks the boundary between two crustal sections of very different origin and age: the upper section formed about 180 million years ago at the edge of the Eurasian Plate, while the lower section originated from the Yangtze continent around 130 million years ago and collided with the upper section roughly 70 million years ago. Today the fault is an active right-lateral strike-slip structure moving at 5 to 10 millimeters a year, a slow rate that makes its motion difficult to detect by GPS even though its direction matches the oblique convergence measured at the nearby Nankai Trough; despite generally lower seismicity than surrounding fault zones, it has produced earthquakes of magnitude 6 to 7 across a documented history of roughly 3,000 years. This entity documents the Median Tectonic Line specifically as a geological formation, focused on its trace through Japan.