The length of the surface fault that caused the Qayen earthquake of Ms: 7.1 on 10 May,1997 at 12: 27(local time) is 110km. The major fault has the trend N30°W but change its orientation to N25°E at the northern end. The right-lateral displacement was 1.7m (average) and 2.1m (maximum). A living tree was torn in tow by the fault displacement. The northern 30km of the surface fault overlap the fault that caused the 1979 earthquake. This fault length of 110km is longer than would be expected from the magnitude of the event (Ms: 7.1).
The Tsugaru Mountains are bounded by active faults and flexures along both western and eastern margins. The western marginal fault zone are reexamined by large-scale airphotograph interpretation, leveling and seismic refractive survey. This fault zone are characterized by west-dipping flexure with east-dipping fault (back thrust) in the southern part, and is not recognized in the northern and central part. Thus, the parameters of this fault zone was revised to be ca.15km long and in the vertical slip rate of ca.0.2m/ka in the late Quaternary time. The Namioka flexure near the fault zone has relatively high vertical slip rate of 0.7m/ka. These active tectonic structures are possibly sesimogenic, but their last events still unclear with implication of the historical 1766 earthquake (M71/4).
The Kamogawa Garben striking W-E across the southern part of the Boso Peninsula is bounded of the northern marginal fault and the southern marginal fault. We examined the Holocene activity of these faults, (1) The northern marginal fault of Kamogawa Gaeben has no evidence of faulting since about 6,000yrs B. P.. (2) The southern marginal fault of Kamogawa Gaeben has been active in the mean rates of vertical displacement of 0.2∼0.6mm/years in Holocene time. At least three faulting events are recognized and vertical slip of single event is 1.1∼1.4m. The mean recurrence interval is estimated to be 2,000∼3,000 years. The last faulting event occured before 1703 AD∼2,850 B. P..
Trench excavation investigation revealed that there are at least two seismic faulting events produced by slips on the Gosukebashi fault during the past 6,000 years in the southeastern Rokko Mountains, Japan. Radiocarbon dating and analytic results of volcanic ash show that the alluvial deposits yielded an age of 1,010±70 y. B. P. and the terrace deposits including Kikai-Akahoya volcanic ash yielded an age of 6,300 y. B. P. were displaced by faults. The younger deposits were displaced at least 1 m in horizontal and the terrace deposits including Kikai-Akahoya volcanic ash were displaced about 2 m in vertical. These data indicate that the last seismic faulting event is probably associated with the 1596A. D. Keicho-Fushimi earthquake and the second event occurred in the period between 6,000 y. B. P. and 1596A. D.
The Negoro fault, a segment of the Median Tectonic Line(MTL) active fault system in the western part of Kii peninsula, marks a southern range front of the Izumi Range, where its late Quaternary faulting is well defined on the topography and geology. We have carried out several drillings and two trench excavations across this fault at Imataki(Nioh-dani valley), where the terrace riser of low terrace 2 surface formed at ca 20,000 years ago is right-laterally dislocated about 50m with vertival displacement (ca 6.5-7m) of northside uplifting component. By these surveys clear fault contacts between the basement and the Quaternary deposits were observed on the trench walls and characteristics of the Negoro fault have been clarified as follows: 1)The fault shattered zone exposed on both sides of trench wall is composed of the Cretaceous Izumi sedimentary rocks, ryolitic rocks intruded to the fault zone in the Miocene and Sambagawa metamorphic rocks, arranging from the north to the south. This zone dipping to the north is thrust over Holocene sediments with angles of 25°∼60°. Therefore, this fault zone corresponds to the geologically defined MTL in the narrow sense. 2)The latest event of this fault had occurred during deposition of the G1 formation. This event is estimated to be after about 3,400yBP and before 1,750yBP on carbon-14age(calibrated calender years are BC173y and AD265y, respectively). 3)The vertical displacement at this event was about 1m, uplifting to the north-side. The faulting had associated the predominantly right-lateral displacement, comsidered from the lateral offset of the valley fill deposits across the fault and striations dipping with angle of 30°on the fault plane.4)The recurrence interval of this fault is estimated to be 2,000∼3,000 year. The right lateral displacement at the latest event was about 4∼10m, considered from the average slip rate and amount of vertical displacement at this event.5)Almost same type of late Quaternary faulting has been clarified by recent researches in the Tokushima plains. However, fault behaviors such as the time of latest event, cumulative displacement, amount of displacement at one event and average slip rate are fairly different.
The Kego fault extends from Fukuoka City to Chikusino City, in North Kyushu. Recently, we made a trench across the fault at Osano, Dazaifu City near the southern end of the fault zone. The fault exposed was a west-dipping reverse fault, though the striation on the fault plane suggested larger strike-slip component. The late Quaternary strata younger than about 32,000 years B. P. on the Mesozoic granite were displaced about 65cm with the western side upthrown at the basal part. Deformation with steep flexures partly overturned in the middle and a gentle warping in upper horizons was dominated on the upward extension of the fault. The vertical displacement, about 65cm, of ca.32,000 years old strata, indicates about 0.02mm/year in an average rate of vertical displacement of the fault. The following two events were recognized, which explain the observed fault-related structure. Event 1 between ca.1,500 yr. B. P. and ca.16,000 yr. B. P., in which about 40cm difference in height was produced on the uppermost formation. Event 2 between. ca.25,000 yr. B. P and ca.32,000 yr. B. P., in which the fault moved as much as 25cm in the same sense as Event 1.