Detection of compression structures from SAR ERS imagery: example of the Central Japan seismic area

Abstract

Observations on Synthetic Aperture Radar (SAR) scenes of the European Remote Sensing (ERS) satellite allow a new mapping of active faults in central Japan. Radar images, which are already known to be useful for structural analysis in tensional and strike-slip environments, have proved here to be efficient in compression tectonics settings. In an area where ongoing compression occurs, several types of structures can be detected from SAR ERS imagery, independently from previous knowledge. The analysis gives a coherent pattern of active structures resulting from a stress regime where the maximum stress component σ1 trends N110°E. This stress field is associated both with compression and with a strike-slip regime of deformation. Compression is characterized by~N20°E-trending reverse faults and folds axis. Strike-slip tectonics is characterized by a system of ~N65°E dextral and ~N145°E sinistral conjugate strike-slip faults. We have evidenced new unknown tectonic structures associated with shearing, such as active folds, push-up hills and pull-apart or releasing bend basins filled with Plio- Quaternary sediments. The emplacement of the Ontake San volcano benefits also from tectonic structures deduced from geological remote sensing results: it is rooted upon a N110°E vertical open tension fracture. All these features can be precisely measured and analyzed by radar imagery. This test in central Japan may serve as a case example for methodology in radar imagery analysis and geological mapping. Keywords-SAR ERS-1; Japan; Tectonics, Image Interpretation.