The multiple inverse method applied to meso-scale faults in mid-Quaternary fore-arc sediments near the triple trench junction off central Japan

The multiple inverse method for fault-slip data is applied to meso-scale faults observed in mid-Quaternary fore-arc sediments near the triple trench junction off the Boso Peninsula, Japan. Data from the Otadai, Umegase and Kokumoto Formations were processed, and three stresses were obtained as significant solutions: vertical, axial compression, and triaxial stresses with the σ3 axis in WNW–ESE and NNE–SSW directions. The triaxial stresses were determined from the Otadai and Umegase data. However, the WNW–ESE tensile stress is not detected from the youngest, Kokumoto, suggesting that the stress is older than the formation. The area was subject to a WNW–ESE tensile stress ∼1.2–1.0 Ma, but tensile direction changed to a NE–SW trend thereafter. The succession was simultaneous with a tectonic event in the landward slope of the Sagami Trough, suggesting that the subduction of the Philippine Sea plate affected the stresses in the overriding plate. The older tensile stress was probably a manifestation of the gravitational collapse of the Hayama–Mineoka ridge, which was growing parallel to the trough. The inferred stress history is concordant with the variation of plate convergence at the trough.