5:15 PM - 6:45 PM
[HRE12-P06] Collection of geological information in urban areas and research methods Part2
Keywords:Geo-Informatics, Osaka, Database , subsurface geology, Liquifaction
Last year, we reported on the accumulation of ground information in the Kansai region, and reported that it can be used to identify geological risks (Kitada et al., 2023). In this presentation, we will further report the results of using this information to examine the characteristics of former river channel areas that are closely related to liquefaction. This report includes the content of discussions conducted by the Groundwater Disaster Prevention Committee of the Research Council on Groundwater and Ground Environment.
It has long been thought that the area where liquefaction occurs during an earthquake has a close relationship with the old river channel, and this is an important point to pay attention to when predicting damage. However, the liquefaction damage area caused by actual earthquakes is often distributed over a wider area than the old river channel. In this study, we considered the Yodo River basin as the target area. Liquefaction was confirmed in the Yodo River basin during the 1995 Southern Hyogo Prefecture Earthquake. At this time, the areas where liquefaction was observed were 1) reclaimed land, 2) near the base of the Kamimachi fault, and 3) the Yodogawa river basin. Therefore, in order to eliminate the effects of 1) and 2), we chose the area near Moriguchi City, Osaka as the study site.
Using boring data around the current river in the area, we extracted the Holocene river channel, which forms a shape that is greatly indented downward at the lower end of the Holocene, from the layer thickness distribution of Holocene sediments. Holocene river channels are characterized by being about three times wider than current rivers and river widths shown in flood control topographic classification maps, and include old river channels in flood control topographic classification maps. It has been confirmed that the liquefaction that occurred during the 1995 Southern Hyogo Prefecture Earthquake and the resulting damage distribution area are included in the Holocene river channel. The Holocene river channel is characterized by a greater thickness of Holocene sediment than the surrounding area. Within this range, it was confirmed that the area where liquefaction occurred was an area where a sand layer was distributed in the surface layer.
It has long been thought that the area where liquefaction occurs during an earthquake has a close relationship with the old river channel, and this is an important point to pay attention to when predicting damage. However, the liquefaction damage area caused by actual earthquakes is often distributed over a wider area than the old river channel. In this study, we considered the Yodo River basin as the target area. Liquefaction was confirmed in the Yodo River basin during the 1995 Southern Hyogo Prefecture Earthquake. At this time, the areas where liquefaction was observed were 1) reclaimed land, 2) near the base of the Kamimachi fault, and 3) the Yodogawa river basin. Therefore, in order to eliminate the effects of 1) and 2), we chose the area near Moriguchi City, Osaka as the study site.
Using boring data around the current river in the area, we extracted the Holocene river channel, which forms a shape that is greatly indented downward at the lower end of the Holocene, from the layer thickness distribution of Holocene sediments. Holocene river channels are characterized by being about three times wider than current rivers and river widths shown in flood control topographic classification maps, and include old river channels in flood control topographic classification maps. It has been confirmed that the liquefaction that occurred during the 1995 Southern Hyogo Prefecture Earthquake and the resulting damage distribution area are included in the Holocene river channel. The Holocene river channel is characterized by a greater thickness of Holocene sediment than the surrounding area. Within this range, it was confirmed that the area where liquefaction occurred was an area where a sand layer was distributed in the surface layer.