, also Median Tectonic Line (MTL), is Japan's longest fault system. The MTL begins near Ibaraki Prefecture, where it connects with the Itoigawa-Shizuoka Tectonic Line (ISTL) and the Fossa Magna. It runs parallel to Japan's volcanic arc, passing through central Honshū to near Nagoya, through Mikawa Bay, then through the Inland Sea from the Kii Channel and Naruto Strait to Shikoku along the Sadamisaki Peninsula and the Bungo Channel and Hōyo Strait to Kyūshū.
The sense of motion on the MTL is right-lateral strike-slip, at a rate of about 5–10 mm/yr. This sense of motion is consistent with the direction of oblique convergence at the Nankai Trough. The rate of motion on the MTL is much less than the rate of convergence at the plate boundary, making it difficult to distinguish the motion on the MTL from interseismic elastic straining in GPS data.
History
The upper part of the Japanese islands was created at the edge of the Eurasian plate 180 million years ago. Then, 50 million years later, the lower part was created at the southern part of the Yangtze continent. The lower part then rode on the Izanagi plate and moved to the upper part. These islands were joined into one and formed the Japanese islands 70 million years ago. The boundary line between the upper part and lower part is the MTL.
Seismic activity
The most important part of the MTL is called which is an active fault and considered hazardous. It is separated into six regions defined by the most recent seismic activities. Although the MTL is a less seismically active region than others, earthquakes with magnitudes of 6 to 7 have occurred. The oldest known activity occurred about 3000 years ago, and the most recent in the 16th century. It is expected that seismic activities will continue in the future. The boundaries of the regions are still being discussed, so the regions are not well defined.
East edge of Kongō Range (between Osaka Prefecture and Nara Prefecture) Expected magnitude of earthquake: 6.9 Probability of earthquake: 0 to 5% within 30 years Most recent activity: From 2000 years ago to the 4th century South edge of Izumi Mountains (between Osaka Prefecture and Wakayama Prefecture) Expected magnitude of earthquake: 7.6 to 7.7 Probability of earthquake: 0.07 to 14% within 30 years Most recent activity: In the 7th to 9th century Kitan Strait (between Wakayama Prefecture and Hyōgo Prefecture) – Naruto Strait (between Hyōgo Prefecture and Tokushima Prefecture) Expected magnitude of earthquake: 7.6 to 7.7 Probability of earthquake: 0.005 to 1% within 30 years Most recent activity: 3100 to 2600 years ago Sanuki Mountains (between Kagawa Prefecture and Tokushima Prefecture) – Eastern part of north edge of Ishizuchi mountains (between Ehime Prefecture and Kōchi Prefecture) Expected magnitude of earthquake: 8 Probability of earthquake: 0 to 0.4% within 30 years Most recent activity: In the 16th century North edge of Ishizuchi mountains (between Ehime Prefecture and Kōchi prefecture) Expected magnitude of earthquake: 7.3 to 8 Probability of earthquake: 0 to 0.4% within 30 years Most recent activity: In the 16th century Western part of south edge of Ishizuchi mountains – Iyonada (Between Ehime Prefecture and Kōchi Prefecture – southern part of Seto inland sea) Expected magnitude of earthquake: 8 or above Probability of earthquake: 0 to 0.4% within 30 years Most recent activity: In the 16th century..
Notable earthquakes
The Great Hanshin earthquake of 1995 occurred on the Nojima Fault, a branch of the MTL. Approximately 6,434 people lost their lives; about 4,600 of them were from Kobe. It caused approximately ten trillion yen ($100 billion) in damage, 2.5% of Japan's GDP at the time.
Regions
Chūbu
The MTL goes from Shizuoka Prefecture to Nagano Prefecture. At Nagano prefecture, it lies between the Ina mountains and the Akaishi mountains. Then, it goes to Chino-shi, the northern part of Nagano prefecture.
Kantō
The MTL goes from Shimonita in Gunma Prefecture to the Hiki hill district in Saitama Prefecture, and then continues down to the Kantō Plain. In the central Kanto Plain, boring tests have shown that the MTL lies 3000 meters beneath ground level in Saitama Prefecture. It is not clear where the MTL goes from there, but it is thought that it passes beneath Kashima or Ōarai on the Pacific coast in Ibaraki Prefecture.