What controls interplate coupling?: Evidence for abrupt change in coupling across a border between two overlying plates in the NE Japan subduction zone

摘要: article i nfo Interplate coupling in the southernmost extent of northeast Japan subduction zone (east off-Kanto, Japan) is investigated detail using a large data set small repeating earthquakes. In this region trench-trench-trench type triple junction, subducting Pacific plate contact with two different overlying plates (the North American and Philippine Sea plates). The border between extending northwestward from junction identified along upper surface based on slip vectors many interplate events including coefficient estimated cumulative earthquakes for period 1993 to 2007 reveals distinct change south (ca. 0.3) north 0.7) across border. This also corresponds southern limit source areas MN7 last 80 years trench, again indicating stronger north. We investigate hypocenter distribution seismic velocity structure boundary number travel-time obtained nationwide seismograph network. results reveal low- just above low seismicity overlain by plate, whereas there are no low-velocity zones high plate. These observations imply that geological difference controls large-scale at interface.