Itoigawa-Shizuoka Tectonic Line

The blue line represents the fault, with the Fossa Magna shaded in orange. The red line indicates Median Tectonic Line.

Itoigawa-Shizuoka Tectonic Line (ISTL) (糸魚川静岡構造線, Itoigawa Shizuoka Kōzō Sen), also Ito Shizu Sen (糸静線) is a major fault on Honshu island that runs from the city of Itoigawa, Niigata Prefecture, through Lake Suwa to the city of Shizuoka in Shizuoka Prefecture. It is often confused with the Fossa Magna (Great Fissure Zone), a geological feature it forms the western boundary of.

Seismic activity

Recent significant earthquakes on this tectonic line include:

• M5.4; 30 June 2011; epicentre near Matsumoto, Nagano; 1 death, 17 injuries.
• M6.7; 22 November 2014; epicentre near Hakuba, Nagano; 46 injuries.