Relationship between seismicity and geologic structure in western Japan

Most large on-shore shallow earthquakes in western Japan have been associated with faults having a previous history of Quaternary displacements. However, the number of such Quaternary faults is very great and their average length is short, so that identification of the most active and dangerous faults is more difficult than in areas such as California or New Zealand that are dominated by obvious master faults. Physiographic features of Quaternary faulting are far more abundant in western Japan than has usually been thought by geologists. Difficulty in recognition has been caused by heavy vegetation, a long history of agricultural modifications, recent volcanism, and numerous massive landslides. The most active-appearing faults trend either northwest or northeast, with predominantly strike-slip displacements of late Quaternary age reflecting east-west compression with remarkable uniformity. The overall pattern is a mosaic-like structure of individual crustal blocks; only the Median Tectonic Line and the Fossa Magna -- both rejuvinated features with earlier histories of vertical displacement -- have demonstrated lengths of active strike-slip faulting exceeding 100 km. Rates of displacement on individual faults, based on C_(14) ages of displaced terraces, are generally an order of magnitude less than that of the San Andreas fault, although the cumulative total may be greater. Some of the highest rates are on faults without large documented historic earthquakes, such as along the Median Tectonic Line in Shikoku. No creep has as yet been observed on major active faults

Late Holocene faulting along the Kawakami fault, an active segment of the Median Tectonic Line, southwest Japan

The Median Tectonic Line active fault zone (MTL), with slip rates as high as 5-10 mm/yr, is one of the most active inland faults in Japan. However, the seismic hazard evaluation on the MTL is hampered by insufficient paleoseismological data, mainly due to sparse distribution of trenching sites along the fault zone. We have conducted a first major paleoseismological study of the Kawakami fault, a segment of the MTL in northwestern Shikoku. The study includes aerial photograph interpretation and paleoseismic trenching. Two trenches were excavated across the Kawakami fault northeast of downtown Komatsu, Ehime Prefecture in 1997. The sediments exposed on the walls in the eastern trench are middle to late Holocene fluvial deposits ranging in texture from silt to gravel. These sediments are offset along an almost vertical, 3-m-wide fault zone. The sense of apparent displacement across the fault zone is down to the north, consistent with Holocene scarps around the trench site. The sediments in the trench contain evidence for three episodes of surface-rupturing earthquake in the past 4000 years B.P. The most recent surface-rupturing earthquake, event A, on the Kawakami fault occurred sometime during the 7th and 19th century AD. Historical documents report extensive damage around the trench site during an earthquake in 1596, and this earthquake may be correlated to the latest faulting on the Kawakami fault. The penultimate event, event B, occurred sometime during the 1st and 10th century AD. Another earthquake, event C, occurred after the deposition of layer Ⅶ, which was radiometrically dated at about 4000 years B.P

Fault displacement along the Naruto-South fault, the Median Tectonic Line active fault system in the eastern part of Shikoku, southwestern Japan

The Naruto-South fault is situated of about 1000m south of the Naruto fault, the Median Tectonic Line active fault system in the eastern part of Shikoku. We investigated fault topography and subsurface geology of this fault by interpretation of large scale aerial photographs, collecting borehole data and Geo-Slicer survey. The results obtained are as follows; 1) The Naruto-South fault runs on the Yoshino River deltaic plain at least 2.5 km long with fault scarplet. the Naruto-South fault is oblique by about 5-10°clockwise to the strike of the Naruto fault. 2) Geologic boundary (MTL) suggested by borehole data, extends between Himeta and Ote-Beach about 8 km long, buried under alluvial deposits. The strike and location is consistent with the Naruto-South fault and submarine fault. Therefore, the Naruto-South fault is presumed to have dislocated using the part of fault plane of the geologic boundary fault. 3) We investigated to detect marks of the last faulting event by use of Geo-Slicer, and we confirmed a active fault with lateral slip component

Latest Rupture Event of the Mino Fault, the Median Tectonic Line Active Fault System, in East Shikoku, Southwest Japan

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 strike-slip 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

Generation of Brain Microvascular Endothelial-Like Cells from Human Induced Pluripotent Stem Cells by Co-Culture with C6 Glioma Cells

<div><p>The blood brain barrier (BBB) is formed by brain microvascular endothelial cells (BMECs) and tightly regulates the transport of molecules from blood to neural tissues. <i>In vitro</i> BBB models from human pluripotent stem cell (PSCs)-derived BMECs would be useful not only for the research on the BBB development and function but also for drug-screening for neurological diseases. However, little is known about the differentiation of human PSCs to BMECs. In the present study, human induced PSCs (iPSCs) were differentiated into endothelial cells (ECs), and further maturated to BMECs. Interestingly, C6 rat glioma cell-conditioned medium (C6CM), in addition to C6 co-culture, induced the differentiation of human iPSC-derived ECs (iPS-ECs) to BMEC-like cells, increase in the trans-endothelial electrical resistance, decreased in the dextran transport and up-regulation of gene expression of tight junction molecules in human iPS-ECs. Moreover, Wnt inhibitors attenuated the effects of C6CM. In summary, we have established a simple protocol of the generation of BMEC-like cells from human iPSCs, and have demonstrated that differentiation of iPS-ECs to BMEC-like cells is induced by C6CM-derived signals, including canonical Wnt signals.</p></div