Abstract
A 3.5-km-long shallow seismic reflection profile was acquired along Yodo riverbank across the active Uemachi fault, Osaka City, Japan. The study aimed to explore the subsurface geological structures in and around the Uemachi active fault system and to assess the feasibility of using reflection seismology to investigate subsurface structure in urban areas where large amount of cultural noise is expected to interfere with the seismic signal. Field recording parameters were adapted to the accessibility limitation and safety precautions in the study area.The quality of collected data was marginal and the signal to noise (S/N) ratio was considerably low. The data processing involved intensive frequency-wave number (f-k) filtering and summing adjacent common midpoints (CMPs) before stack as well as weighted stacking. The f-k filtering removed most of the ground roll and guided waves while summation of adjacent common midpoints increased the fold and enhanced the apparent signal to noise ratio of the final section. Trace weighting before stack was remarkably effective in increasing the identity and continuity of reflections. The visual and statistical comparison between weighted stack and the basic stack proved that weighted stacking produces significantly more coherent section.The interpretation of the final seismic section and the correlation with the borehole data in the vicinity confirmed the location of the Uemachi fault plane. The fault is shown in the seismic section as a reverse fault that dips to the east with an angle of about 75 degrees . The seismic line also revealed the possibility of the presence of other two shallow faults on the hanging wall of the Uemachi fault. The two faults are dipping to the same dip direction of Uemachi fault with slightly larger dip angle. Abstract Copyright (2002) Elsevier, B.V.