Birth of a major strike-slip fault in SW Japan

A 500 km-long strike-slip fault, the North Chugoku Shear Zone (NCSZ) is identified in SW Japan, responsible for four M > 7 earthquakes in the past 130 years. A new geodynamic mechanism of increased interplate coupling above an obliquely subducting flat slab is presented to explain the transfer of trench parallel motion 400 km inland from the Nankai Trough, to the level of the Quaternary adakitic volcanic arc. While Quaternary dextral strike-slip motion is widely believed to have occurred along the Median Tectonic Line (MTL), near the Miocene volcanic arc, the central segment in Shikoku has shown little seismicity for the last 1000 years. Pure dextral strike-slip focal mechanisms for 15 modern and historical events indicate that part of the transcurrent motion is being transferred from the MTL to the NCSZ.