Abstract
A 500 km-long strike-slip fault, the North Chugoku Shear Zone(NCSZ) is identified in SW Japan, responsible for four M 4 7earthquakes in the past 130 years. A new geodynamic mechanismof increased interplate coupling above an obliquely subductingflat slab is presented to explain the transfer of trench parallelmotion 400 km inland from the Nankai Trough, to the level of theQuaternary 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 centralsegment in Shikoku has shown little seismicity for the last 1000years. Pure dextral strike-slip focal mechanisms for 15 modernand historical events indicate that part of the transcurrent motionis being transferred from the MTL to the NCSZ.