There are many high-level gentle slopes in the Asan (Sanuki) Mountains, north-eastern Shikoku. The writer classified them into three ; top gentle slopes (T slopes), top-flank gentle slopes (TF slopes), and flank gentle slopes (F slopes). He surveyed mainly their distribution and characteristics, and discussed their formation. Following are conclusions; 1. High-level gentle slopes occupy 31.9% area in the western part of the Mountains, 50. 9 % in the central, 17. 6% in the eastern. When seen in the N-S direction, at the right angle with the base-line along the Median Dislocation Line, which is one of the 1st class tectonic lines in Japan, 88% of the high-level gentle slopes are in the zone between the base-line and 6 km north of it, especially 56. 1% of the whole are in the zone 2 to 4 km north of the base-line. 2. There are many relationships between distribution of the high-level gentle slopes and the geological structure of the Izumi Group constituting their base rock. The large portion of F slopes are near its synclinal axis, and many of TF slopes are near the southern limb of the syncline. The greater part of F slopes have steep cliffs at their back-ground and small mounds and slight depressions on their surfaces. As to the geological profiles observed at many outcrops showing deposition of detritus and some bedding of base rock, it is probable that F slopes were resulted from the mass sliding on the back slopes of cuesta. The characteristics of T slopes are different from those of F slopes, but it is not yet solved whether T slopes are the relics of uplifted peneplains or not. 3. Although it was reported that some portion of the high-level gentle slopes belonged to the piedmonttreppen, the writer cannot discover the clear evidences, but at the present stage he cannot deny the piedmonttreppen theory, because some high-level gentle slopes, e. g. those in the north of the Awa-Ikeda Station or in the north of Kamiitacho, have the accordant levels and it is more reasonable to attribute their formation other than landslide. 4. The asymmetric distribution of the high-level gentle slopes in the N-S direction is one of the notable characteristics. The earlier upwarping in the northern part has the high-level gentle slopes eroded out and the later upheaval in the southern part along the Median Line made the slopes……T slopes perhapss……remained without dissection. 5. Relationships between the high-level gentle slopes and facies of the Izumi Group are not clear at present.

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徳島県吉野川北岸地域の中央構造線において,大縮尺空中写真判読と現地調査をもとに,活断層の分布と運動様式の再検討を行った.その結果,従来断層が連続しないと考えられていた地域をつなぐような断層が,新たに確認された.吉野川北岸での中央構造線は,鳴門断層の西端部付近に不連続が存在する可能性は残るものの,鳴門断層から父尾断層まで湾曲や屈曲を伴いながら,ひとつづきの断層として連続することが明らかになった.
また,横ずれ断層の南側に低角な逆断層(前縁逆断層)の認められる地域がある.前縁逆断層は,(1)主断層の走向がその一般走向に対してやや斜交する(10～20°反時計回り)部分で,その南側に平行して存在する場合と,(2)主断層がその一般走向に対して大きく屈曲する位置で,その南側に存在する場合とがある.(1)は,横ずれ断層の走向の変化によって生じた水平短縮量の増大によって生じ,(2)は,断層の屈曲に伴う局地的な圧縮応力によって生じたと考えられる.

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The Median Tectonic Line (MTL) active fault system is one of the most active intraplate faults in Japan. The fault system, which is more than 300 km long, is a right-lateral strikeslip fault with an average slip rate of 5-10 mm/y in east Shikoku. The 13.5-km-long Mino fault of the MTL active fault system is located at the western part of Tokushima Prefecture in east Shikoku. We carried out trench excavation surveys of the Mino fault at Ueno in Mino Town and Ikenoura in Mima Town. Both sites are situated at fault depressions formed on the middle and lower terrace surfaces by the activity of the Mino fault. Fault depression deposits consist of younger and finer grained layers with abundant 14C dating samples. We inferred the dates of faulting events from upward fault terminations on the trench walls.
At Ueno, it is recognized that the latest rupture event occurred between 1, 295-1, 390 cal A.D. and 1, 660-1, 950 cal A.D. (190 ± 50 years B.P.). Multiple faulting events are also suggested after K-Ah ash fall (about 5, 200 B.C.), because the ash layer steepens to near vertical. At Ikenoura, the latest rupture event is estimated to have occurred after 1, 525-1, 660 cal A.D.
Taking account of the previous reports on the eastern extension at Chichio and Zunden faults, we conclude that the MTL active fault system in east Shikoku ruptured in the 16th century A.D. or later. The liquefactions, which occurred between the latter half of the 16th century A.D. and the beginning of the 17th century A.D., are recognized at archaeological sites at Maruyama and Ogaki in the western part of Tokushima Prefecture. These sites are located immediately south of the Mino fault and the Ikeda fault to the west. This fact suggests that the liquefactions were caused by faulting of the MTL active fault system in east Shikoku.

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