1:45 PM - 2:00 PM
[HQR05-13] Using microtremors to discriminate similar types of slightly elevated topographies: A case of the Itoshima Lowland, Fukuoka Prefecture
Keywords:microtremor observation, Aso-4, natural levee, isolated hill
In alluvial lowlands, there are several types of slightly elevated topographies including natural levees around river channels, in addition to that, fragmented residual terraces are sometimes distributed. It is important to distinguish between these natural levees and fragmented terraces not only in terms of local land history, but also disaster prevention, because ground properties such as liquefaction susceptibility are considered to depend on subsurface geology.
When terraces and natural levees have similar morphology, it is difficult to discriminate them from geographical maps or aerial photos. However, excavation surveys are effective but time-consuming and expensive, and limited in terms of areal data collection. Therefore, the authors focused on ground properties based on microtremor data as non-destructive and handy method. Last year we conducted verification surveys around the Kazo Lowland of Saitama Prefecture and found that under the certain conditions it is possible to discriminate between the late Pleistocene Omiya terrace and natural levees based on phase velocity and frequency of microtremor data (Komatsubara et al., 2024).
To see if this method can be applicable to other alluvial lowlands, we conducted the same type of microtremor observation in the Itoshima Lowland of Fukuoka Prefecture in February 2025, where irregularly shaped slightly elevated topographies of 1-2 m are distributed, consisting of either natural levees, terraces, or Aso-4 pyroclastic flow deposits (Fukuoka Prefecture, 1985; Kubo et al., 1993). On this survey, microtremor observation was conducted at a total of 14 points on the Aso-4 depositional surface, natural levees, floodplains, and terrace surfaces, where subsurface geology was confirmed by the soil cane survey by Sato and Mizuno (2023), or the classification is clear from topographic interpretation. The data will be processed to determine the extent to which the microtremor observation data reflects the subsurface of those slightly elevated topographies and whether it is applicable to the identification of geology in this area.
References
Fukuoka Prefecture, 1985, Subsurface Geological Map, Maebaru and Genkai Island. Fukuoka Prefecture.
Komatsubara, J., Cho, I., Naya, T., Sato., Y., and Senna, S., 2024, Using microtremors to discriminate two similar types of slightly elevated topographies: A case of the Pleistocene Omiya terrace from Holocene natural levees, Saitama, Japan. JpGU Annual Meeting 2024 abstract HQR05-P06.
Kubo, K., Matsuura, H., Ozaki, M., Makimoto, H., Hoshizumi, H., Kamata, K., and Hiroshima, T., 2003, 1:200,000 Geological Map, Fukuoka., Geological Survey of Japan.
When terraces and natural levees have similar morphology, it is difficult to discriminate them from geographical maps or aerial photos. However, excavation surveys are effective but time-consuming and expensive, and limited in terms of areal data collection. Therefore, the authors focused on ground properties based on microtremor data as non-destructive and handy method. Last year we conducted verification surveys around the Kazo Lowland of Saitama Prefecture and found that under the certain conditions it is possible to discriminate between the late Pleistocene Omiya terrace and natural levees based on phase velocity and frequency of microtremor data (Komatsubara et al., 2024).
To see if this method can be applicable to other alluvial lowlands, we conducted the same type of microtremor observation in the Itoshima Lowland of Fukuoka Prefecture in February 2025, where irregularly shaped slightly elevated topographies of 1-2 m are distributed, consisting of either natural levees, terraces, or Aso-4 pyroclastic flow deposits (Fukuoka Prefecture, 1985; Kubo et al., 1993). On this survey, microtremor observation was conducted at a total of 14 points on the Aso-4 depositional surface, natural levees, floodplains, and terrace surfaces, where subsurface geology was confirmed by the soil cane survey by Sato and Mizuno (2023), or the classification is clear from topographic interpretation. The data will be processed to determine the extent to which the microtremor observation data reflects the subsurface of those slightly elevated topographies and whether it is applicable to the identification of geology in this area.
References
Fukuoka Prefecture, 1985, Subsurface Geological Map, Maebaru and Genkai Island. Fukuoka Prefecture.
Komatsubara, J., Cho, I., Naya, T., Sato., Y., and Senna, S., 2024, Using microtremors to discriminate two similar types of slightly elevated topographies: A case of the Pleistocene Omiya terrace from Holocene natural levees, Saitama, Japan. JpGU Annual Meeting 2024 abstract HQR05-P06.
Kubo, K., Matsuura, H., Ozaki, M., Makimoto, H., Hoshizumi, H., Kamata, K., and Hiroshima, T., 2003, 1:200,000 Geological Map, Fukuoka., Geological Survey of Japan.