6:15 PM - 7:30 PM
[SSS28-P24] Activity of the Northern Marginal Faults of the Saga Plain
Keywords:Northern Marginal Faults of the Saga Plain, normal fault, large-scale geographical map, tectonic bulge, interpretation of microtopography
In interpretation of microtopography, we created contour maps of 1m intervals from city planning 1:2500 maps. And we used aerial photographs of scale of 1 per million taken that GSI was taken in the 1960s. Also, we conducted a field survey, including simple boring survey and ultra-shallow seismic reflection profiling.
Resulting in, terraces surface classification of the north portion of the Saga plain has been divided into 7 side of as follows:[the higher than] H, M1, Aso-4pyroclastic flow depositional surface, M2, L1, L2 andL3. Also, light of the comparison with the terraces classification diagram studied (the late Nagaoka originals; Shimoyama, 1999; Shimoyama et al., 1999, 2010, etc.) so far, each of the formation age is as follows. H surface MIS7 equivalent, M1 surface is located in the lower Aso-4 pyroclastic flow deposition surface, it is MIS5e equivalent of last interglacial period, Aso-4 pyroclastic flow deposit surface is 8.9ka and M2 surface is MIS 5a equivalent the formation age from such be covered discordance Aso-4.
Further, L1 surface in terms of the most widely distributed in this study area, it is the Last glacial epoch (MIS 2-4 equivalent) because AT(26-29ka) was sandwiched directly above emerged surface, L2 surface is MIS 1 equivalent for just above the K-Ah (7.3ka) on emerged surface, L3 surface is MIS 1 equivalent lower than L2 surface.
In these L2 surface was observed tectonic bulges lie on the southern side of the known fault trace that continues in the east-west direction. These tectonic bulges are anticline-like, decrease flexure to the south and these states can be read also from the detailed contour map. According to surface exploration, these tectonic bulges have slightly tilted to be confirmed visually. In addition, a simple boring survey around the L2 side with these tectonic bulges, was carried out plurality of places in the hanging wall side footwall side of the fault trace. As a result, relative uplift side of the fault trace on L2 surface in Kawakubo Saga city (altitude about 5m), K-Ah was found in depth 102~105cm, and AT was found in depth 120 ~ 126 cm. For this presentation, we got some results by drilling survey, surface exploration and Ultra-shallow seismic reflection profiling. So we described the discussion on the activities of the active faults in the Northern Marginal of the Saga Plain.