The blue line to the left represents the fault, with Fossa shaded in red.
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 Fossa Magna which lies to the east.
Recent significant earthquakes on this tectonic line include:
Coordinates: 35°29′28.4″N 138°19′33.6″E / 35.491222°N 138.326000°E