生駒山地と大阪平野境界部における反射法地震探査

Abstract

The common mid-point (CMP) reflection survey was conducted on three measurement lines with a length of about 1km to reveal the subsurface structure of the peripheral zone between the Ikoma mountains and the Osaka basin. We obtained the following results. The depth sections of two of the measurement lines show the same feature: sediments are stratified horizotally below almost the whole line and are pulled up below a marginal portion close to the Ikoma mountains, suggesting a high-angle reverse fault. Beneath the remaining line, sediments dip toward the Osaka basin, suggesting the hasement also dips, and several faults were detected. Although basin-bedrock interfaces were not detected in the three profiles, they are estimated to be at a depth of about 1.7km from the analysis of the Bougoer anomalies, incorporating the results of the reflection survey. Comparison of the profiles of lines 1 and 3 with the profile in the Osaka bay zone demonstrates that the configuration of the sediment in the peripheral zone is the same as that in the Osaka bay zone. The sediments are divided into two layers: in the upper layer marine and non-marine deposits stack alternately and in the lower layer only non-marine deposits stack.