Ground penetrating radar investigations across the Uemachi fault, Osaka, Japan

A ground penetrating radar (GPR) survey was conducted across the well-known Uemachi fault system in order to investigate the shallow geological structures in the vicinity of the fault zone. Field acquisition parameters were selected after collecting several test profiles to find out the most adequate gain, time range and wave frequency. Twelve GPR profiles and six wide-angle retraction reflection (WARR) profiles were acquired in the area. Basic processing was applied to the data in order to reduce artifacts and noise in the original data. The interpreted GPR profiles clearly show the location and the geometry of a subsurface fault scarp that has a visible expression at the surface as well as several subsurface fault strands. The subsurface faults and fractures mainly trend in the north-south direction, parallel to the strike of Uemachi fault plane. Most of these fault strands extend for long distance so that they could be easily traced from one profile to the next. The field survey shows that deformational structures are reasonably concentrated near the Uemachi fault zone. The intensity of fault strands increases with increasing depth and towards the south at the study site. The hazardous zone around the fault can be easily avoided in future building and development as the planes of weakness are concentrated near the fault plane and completely disappear at distances less than 100 m away from the fault plane. (C) 2003 Elsevier Science B.V. All rights reserved.