定常観測網から得られた首都直下の三次元地震波速度構造

Many researchers have studied the three-dimensinal seismic velocity structure beneath the Kanto region, central Japan using seismic tomography, because the structure is very complicated due to subducting of the Pacific and the Philippine Sea plates beneath the Eurasian plate. The Tokyo metropolitan area is located in the Kanto region. Initially, the subducting Pacific and Philippine Sea plates are imaged with high-velocity zones. With many data, the oceanic crust at the uppermost part of the subducting Philippine Sea plate was imaged clearly. After construction of the NIED Hi-net, the oceanic ocrust of the Pacific plate subducting to depths over 100km was also imaged. A large low-velocity region at depths of 30－50km beneath the central Kanto region in the east-west direction was found by many researchers. The reason for the low-velocity is considered to be the existence of a serpentinied mantle wedge, curling Eurasian crust, and thick oceanic crust of the Philippine Sea plate. A low-velocity zone at depths of 40－70km beneath the eastern Kanto region with north-south direction was also found. The reason for this low-velocity is considered to be the existence of serpentinied mantle wedge and curling Philippine Sea plate. A high-density seismograph network, called MeSO-net, is under construction in this metropolitan region. The results with these data are expected to reveal a more detailed structure beneath the metropolitan area. We review former studies on the velocity structures beneath the Kanto region and note some characteristic structures beneath the Kanto region with results along arrays of MeSO-net