A seismic survey was conducted across the Tachikawa active fault in the western suburbs of Tokyo metropolitan area. The deep structure and movement of the fault are discussed based on the CMP stacked seismic section together with the geological data published previously. The results are as follows:
(1) A flexure, about 150 meters in width, underlies the flexure scarp of the fault and continues vertically down to 1000 meters in depth.
(2) The displacement of the fa u lt is about 100 meters upthrow of the northeast side between 300meters and 600 meters in depth, while the displacement at basement depth is about 100 meters downthrow of the northeast side.
(3) The northeast side o f the fault had subsided relatively to the southwest side in the past. The fault movement was stopped for a while. Then the fault movement was reversed and the northeast side has been upheaved up to now. This is an inversion tectonics of the fault movement.