知多半島西岸沖の伊勢湾断層 The lse Bay Fault off the Chita Peninsula, Central Japan
Construction of the Chubu International Airport has started off Tokoname City (Chita Peninsula) in Ise Bay, Central Japan. Various surveys such as bathymetry, seafloor drilling, sonic prospecting, and geologic examinations of recovered borehole core samples have been performed to reveal soil engineering characteristics, submarine topography, submarine geology, and the precise locality and mode of movement of the Ise Bay Fault at the bay area (Chubu Kukou Chousakai=The Chubu International Airport Research Foundation, 1994). Many fruitful results on the Ise Bay Fault have been gained, as follows:<BR>(1) The bay area is underlain by the A (Holocene), B (upper Pleistocene), C1-C2 (upper to middle Pleistocene), and T (basement) Formations, in descending order. The A, B, C1, and C2 Formations are correlated with the Nan'yo, Nohbi-First Gravel-Toriimatsu Gravel, Atsuta (lower part), and Ama Formations below the Nohbi Plain, respectively. The basement T Formation corresponds to the Mio-Pliocene Tokoname Group.<BR>(2) The Ise Bay Fault extends several kilometers off the west coast of Chita Peninsula, parallel with the coast line, downthrown on the Ise Bay (west) side.<BR>(3) Mode of faulting is divided into three types, namely, <BR>a) flexure type in the northern part.<BR>b) steeply westward dipping type with small-scaled thrusts downthrown Chita Peninsula (east) side in the middle part.<BR>c) high-angle faulting type in the southern part.<BR>(4) Mean vertical slip of the Cl Formation is measured 46, 42, and 35 meters in the southern, middle and northern part, respectively. Vertical slip of the B Formation measures 2-11 and 2-5 meters in the southern and middle part, respectively, and is not clearly detected in the northern part because of horizontal bedding. Accordingly, the fault is inferred to be more active in the southern and middle parts.<BR>Based on the above mentioned results, the Ise Bay Fault is evaluated as follows, <BR>(5) The average slip rate of vertical displacement ranges from 0.23 to 0.45 meters per 1000 years, which ranks Class B (lower) in the degree of activity.
地學雜誌 109(1), 10-26, 2000-02-25
Tokyo Geographical Society