Abstract
The southern Hyogo area, southwest Japan, is well known to have suffered from a large earthquake occurred during January 17, 1995. Although many active faults are distributed in this area, their orientations (dip directions and dip angles) have not yet been clarified from the geologic field investigations. For this problem, we have constructed the estimation and interpretation methods of fracture orientation through a combination of satellite-image derived lineaments, digital elevation model (DEM) data, and digital geologic map. This method is founded on directional relationship between the derived lineament and the slope produced by the DEM. The lineaments are extracted automatically using the Segment Tracing Algorithm (STA). The advan-tages of the STA are its capability to extract lineaments that parallel the sun's azimuth and those located in shadow areas.
Lineament analysis was accomplished by using three types of satellite image : LANDSAT TM, SPOT HRV, and JERS-1 SAR images. At first, the appropriate parameter values used in the STA were determined for each satellite image based on the semivariogram for the gray-levels distribution of the image. It was clarified that most of the estimated fractures have steep dip angles ranging from 80° to 90° and are judged to be reverse fault type. The lineaments extracted from the LANDSAT TM image were found to express appropriately the fracture characteristics of the study area. Azimuthal features of the estimated fractures were common to individual surficial geology. Using the location and orientation of the estimated fracture planes, three-dimensional fracture distribution was visualized. This fracture-distribution model was confirmed to be valid through its relation to the distribution of aftershock hypocenters.
