Research on Quaternary faulting history and long-term seismic evaluation of the Median Tectonic Line (MTL) fault zone in southwest Japan

The Median Tectonic Line (MTL) fault zone is the longest and most acive intraplate fault in the Japanese Islands. The author has pointed out fault topographies accompanied with right-lateral strike-slip faulting and has made clear the average slip-rate of 5-10mm/y in Shikoku and 1-3mm/y in western Kii Peninsula since 1968. And he has carried out trench excavation surveys, detailed mappings (strip maps and precise active fault maps in the scale of 1 : 25,000 ) along this fault zone and proposed the division to the rupture segments on the MTL. Local governments, the Geological Survey, and university researchers have conducted many kinds of mapping and field surveys (drilling, trenching, seismic refraction survey, etc.) of the active faults to assess their earthquake potentials, especially since the 1995 Kobe earthquake. Based on the extensive data obtained by these investigations, the characteristics and chronology of Holocene surface faulting on the MTL have illuminated the slip amount of each event in the latest surface rupture and its date. The most recent rupture on the MTL in Shikoku occurred in the 16th century and is probably correlated to the 1596 Keicho earthquake. It is highly probable that the active faults from the Awaji Islands and the south front of the Rokko Mountains to the Arima-Takatsuki fault zone were activated at the same time. As long-term occurrence probabilities for the MTL fault zone were announced to the public by the Earthquake Research Committee of the Headquarters for Earthquake Research Promotion (2003, 2012), the author commented on these evaluations, the problems remaining and perspectives on the future.