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Abstract To complement historical written records of tsunamis in the Nankai Trough and reconstruct prehistoric tsunami records, we conducted a coring survey at a coastal lowland in Mie Prefecture, central Japan. We found 10 sand layers deposited from about 4500 to 500 years ago. The layers are interpreted as tsunami deposits because of the presence of abundant bioclasts of marine organisms and sedimentary structures such as alternating sub-layers of sand and silt, rip-up clasts, and upward-fining structures, all of which are common in modern tsunami deposits. At the study site, no substantial seawater inundations and sand depositions have been recorded even for the largest typhoons to ever hit the region. There are historical accounts of earthquake and tsunami damage along the Nankai Trough in 1498, 1361, 1096, 887, and 684 CE. Estimated ages of the youngest three sand layers overlap well with tsunamis in 1498, 1096, and 684 CE. Our results support the hypothesis suggested by archaeological studies that the 684 CE rupture extended farther eastward than the historical record indicates or that another tsunami occurred at some time close to 684 CE. We did not find any sand layers that were definitely correlated with the tsunamis of 1361 and 887 CE, which are thought to have occurred by multi-segment ruptures of the Nankai Trough that includes the segment directly offshore from the study site. If the sand layers found at the study site were deposited by the tsunamis of 1498, 1096, and 684 CE, and if the tsunamis of 1361 and 887 CE did not inundate the study site, the tsunami recurrence interval during the relevant time period was about 400 years. This finding does not support the widely believed hypothesis that earthquakes and tsunamis occur at regular intervals of approximately 100 years in this area. In addition, similar to the historical tsunamis, intervals of geologically recorded prehistoric tsunamis at the study site vary from about 100 to 600 years. The hypothesis of variable recurrence of earthquakes and tsunamis along the Nankai Trough should be tested by future geological and historical studies in unbiased way. Highlights • Ten tsunami sand layers were observed on the Pacific coast of central Japan. • Two tsunami deposits were correlated with the tsunamis of 1498 and 1096 CE. • The age range of one tsunami deposit overlapped with the tsunami of 684 CE. • We did not find deposits definitely correlated to the 1361 and 887 CE tsunamis. • Intervals between geologically recorded tsunamis are not constant. [ABSTRACT FROM AUTHOR]

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Abstract: After estimating tectonic uplift rates along the northern part of the northeast Japan forearc (the overriding plate in the northeast Japan subduction zone) by mapping the elevation of the inner edges of marine terrace surfaces, we refined this estimate through elevation measurements of the buried shoreline angle beneath well-dated marine terrace surfaces, from which we could derive more accurate paleo-sea levels. The uplift rate initially inferred from the inner edge of marine terrace T4, correlated with marine isotope stage MIS 5e by tephrochronology, increases eastward from 0.11–0.22mky−1 around the backarc volcanic front to 0.17–0.32mky−1 in the forearc on the peninsula of Shiriyazaki. We refined the uplift rates for T4, on the basis of the shoreline angle elevation, from the reconstructed profile of the paleo-sea cliff and wave-cut platform on a rocky coast and the reconstructed profile of the swash zone sediments and terrace deposits on a sandy coast. The refined uplift rates were 0.14–0.25mky−1 on the rocky coast and 0.14–0.23mky−1 on the sandy coast, slightly slower than the rates we inferred from the height of T4 and about one-half to three-fourths of previously reported rates. By extrapolation from the example of the sandy coast, the refined uplift rate around the volcanic front was 0.09–0.18mky−1. The vertical deformation across the forearc of the Shimokita Peninsula since MIS 5e is possibly associated with regional isostatic uplift of 0.09–0.18mky−1 and anticlinal deformation by an offshore fault, interpreted from acoustic profiles, of 0.05–0.07mky−1. [Copyright &y& Elsevier]

Abstract: When determining deformation along an active strike–slip fault, it is desirable to include the cumulative distributed deformation due to drag away from the fault trace in addition to offset on the fault. We achieve this by integrating geomorphologic, paleomagnetic, and geologic data for the active left-lateral strike–slip Tanna fault zone in central Japan, which previous studies suggest is slipping at about 2mm/yr. We combine new detailed mapping of multiple Quaternary strands of the fault zone with paleomagnetic measurements from volcanic rocks extruded across the faults from the Taga Volcano at about 0.6Ma. From these data we determine differential counterclockwise rotations, from which we infer cumulative strike–slip drag deformation, at distances of about 1–3km from the faults. These results suggest that the total strike–slip displacement accompanying cumulative drag deformation along the fault zone from approximately 0.6Ma to the present is more than 2.3–2.7km (based on a kinematic model), or about 6.0km (based on a power law rheology model), after adding 1km of offset along the fault trace. Thus, depending on the model applied, the total rate of strike–slip deformation along the Tanna fault zone is either more than 3.8–4.5mm/yr, or about 10mm/yr, respectively. Both of these rates are considerably higher than a previous estimate of about 2mm/yr based solely on strike–slip offset without accommodating the drag deformation over the broader zone on either side of the fault break. Furthermore, the deformation rate based on the power law rheology model is comparable to the rate detected by past GPS observations. [Copyright &y& Elsevier]

The late Pleistocene Kamitakara Pyroclastic Flow Deposit (KPFD) and its correlative Kasamori (Ks22) Tephra in central Japan are found to preserve stable thermoremanent magnetization (TRM) and detrital remanent magnetization (DRM), respectively. Untilted site-mean declinations of the KPFD are characterized by a fairly large scatter with easterly deflection, while those of the Ks22 show significantly smaller deflections. Because northerly paleomagnetic directions consistently characterize shallow marine sediments intercalating the Ks22 layer, the directional discordance is not attributed to different acquisition timing between TRM and DRM, but is probably due to a recent tectonic rotation in central Japan. Large scatter in TRM declinations of the KPFD implies that a number of right-lateral active faults around the depositional area of the pyroclastic flow raised differential rotation of crustal blocks in central Japan, even during the late Pleistocene. [ABSTRACT FROM AUTHOR]

Detailed paleomagnetic investigation of a pyroclastic flow deposit has clarified the deformation mode around an active fault. In central Japan, the early Quaternary Nyukawa Pyroclastic Flow Deposit is cut by the active dextral Enako fault. Activity level of the fault is evaluated on the basis of geological and geomorphological surveys. Then, paleomagnetic samples are collected from 22 sites at exposures located on a lineament that is adjoining and parallel to the Enako fault. Stable thermoremanent magnetization (TRM) of the pyroclastic deposit is isolated through progressive thermal and/or alternating field demagnetization tests. Untilted site-mean directions of the TRMs simultaneously acquired during initial cooling indicate significant clockwise vertical-axis rotation. The lineament was then activated with right-lateral motions through the early Quaternary. Together with the late Quaternary activities along the adjoining Enako fault evaluated by our study, the present result exemplifies a migration of active segments within a fault system during the Quaternary. Paleomagnetic directions on the strike–slip fault are not concordant with uniform deformation predicted by the model of rotation of rigid blocks aligned on a master fault, but suggestive of a periodic deformation as a result of intense fracturing and differential rotation of blocks bounded by nested parallel faults. [Copyright &y& Elsevier]

Study Objectives: Sleep problems, such as accumulated sleep loss and social jetlag (SJL), which is characterized by a discrepancy in a person's sleep pattern between the weekday and the weekend, are associated with physical and mental health problems, and academic performance in young ages. However, sex differences in these associations are not fully understood. The purpose of this study was to investigate the effect of sex on sleep-related factors, mental health (negative mood), and academic performance in Japanese children and adolescents., Methods: A cross-sectional online survey was conducted with 9270 students (boys: N = 4635, girls: N = 4635) ranging from the fourth grade of elementary school to the third grade of high school, which typically includes ages 9-18 years in Japan. Participants completed the Munich ChronoType Questionnaire, the Athens Insomnia Scale, self-reported academic performance, and negative mood-related questions., Results: School grade-related changes in sleep behavior (e.g. delayed bedtime, shortened sleep duration, and increased SJL) were detected. Girls had greater sleep loss on weekdays and SJL on weekends than boys. Multiple regression analysis revealed that sleep loss and SJL were more associated with negative mood and higher insomnia scores in girls than in boys, but not with academic performance., Conclusions: Sleep loss and SJL in Japanese girls had a higher correlation to their negative mood and tendency to insomnia than in boys. These results suggest the importance of sex-dependent sleep maintenance for children and adolescents., (© The Author(s) 2022. Published by Oxford University Press on behalf of Sleep Research Society.)