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Many fatigue cracks were reported at welded joints between vertical stiffeners and deck plates in orthotropic steel decks (OSDs) in Japan. These fatigue cracks were caused by restraining deck's deflection by stiffeners. To prevent such cracks, reducing stiffness of stiffener top can be a solution. For newly fabricated OSDs, the Japan Road Association recommends cutting off the top of vertical stiffeners on cross beams. However, stiffeners with the gap have very little vertical load carrying capacity and it could not be applied to main girders. Half-circle notch method is retrofitting method for existing structures. For new OSD structures, it can be installed. Whereas a fillet detail is currently used for the beam-to-column connections of steel bridge frame piers to reduce stress concentration at right-angle corners of flanges. The fillet detail, which has not been considered for stiffeners, may be effective for new OSDs. In this study, fatigue durability of the half-circle notch detail and the fillet detail for new OSDs are evaluated through finite element analyses and fatigue tests using a full-scale specimen. As a result, the fillet detail showed superior fatigue durability without no fatigue cracks, while some fatigue cracks were developed in the half-circle notch detail. [ABSTRACT FROM AUTHOR]

Knowledge of the state of stress in subducting slabs is essential for understanding their mechanical behavior and the physical processes that generate earthquakes. Here, we develop a framework which uses a high-resolution focal mechanism catalog to determine the change in the position of the neutral plane before and after the M9 Tohoku-oki earthquake to determine that the deviatoric stress within the slab at intermediate depths must be very low (~1 MPa). We show that by combining the static stress calculated from coseismic slip distributions with the stress orientations before and after the mainshock, we can determine the full deviatoric stress tensor within the subducting slab at intermediate depths. These results preclude earthquake source mechanisms that require large background driving stresses, favoring a mechanically weak subducting slab, thus providing quantitative constraints on the physical processes that generate intermediate-depth earthquakes. [ABSTRACT FROM AUTHOR]

The long‐stroke electromagnetic repulsion mechanism is subjected to large stresses during the driving phase, and the repulsion disc is prone to fracture due to excessive vibration amplitude up and down. Therefore, it is necessary to reduce the peak stress and vibration amplitude of the repulsion disc, improve the mechanical life, and improve the driving performance without decreasing the motion displacement, but it is not possible to do so at present. To address this problem, this paper takes the 'coil‐repulsion disc type' electromagnetic repulsion mechanism as the research object, and builds a simulation model of electromagnetic repulsion mechanism with structural strength and driving performance by using finite element simulation software, and analyzes the effects of four structural parameters, namely, the height of the repulsion disc, the inner diameter of the repulsion disc, the radius of the circular table and the radius of the chamfer, on the displacement and stress distribution of the model. After that, 39 sets of samples were output by BBD experimental design method, which were introduced into the BP neural network prediction model and combined with NSGA‐II algorithm to optimize the structure of the electromagnetic repulsion mechanism. The simulation results show that with the repulsion disc height of 14 mm, the repulsion disc inner diameter of 14 mm, the radius of the circular table is 29.78 mm and the chamfer radius of 7.06 mm, the peak stress of the repulsion disc of the electromagnetic repulsion mechanism is reduced by 57.83%, the amplitude of the repulsion disc is reduced by 3.24 mm, the peak electromagnetic repulsion force is increased by 7.52 kN and speed at the end of 3 ms increased by 9.8%. Under the condition of satisfying the constraints and increasing the overall displacement, the structural strength is increased and the driving performance of the mechanism is ensured to be improved, providing reasonable mechanism parameters for the opening and closing requirements of the fast mechanical switch. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Arimatsu Narumi Shibori (thread-tying), which is a traditional craft, has a history of more than 400 years and has been handed down to artisans in Japan. Recently, the shortage of successors to artisans has emphasized the maintenance of this thread-tying technique. To achieve this, Arimatsu Narumi Shibori needs to be elucidated based on scientific knowledge using numerical analysis techniques, which has not been achieved so far. In this technique, the fabric is complexly deformed, and complex wrinkles are formed in it. One possible approach for modeling this fabric is the use of a shell element that does not have an element volume. As the tensile and bending stiffnesses of the shell element are evaluated using a single Young's modulus, the bending stiffness increases with the tensile stiffness. Therefore, unlike the deformation achieved by the actual fabric-tying, this fabric analysis model cannot achieve large deformation of the fabric. In this study, a tying analysis method is proposed to elucidate Arimatsu Narumi Shibori. In this method, the fabric is modeled using three layers of shell elements to reproduce the fabric behavior. The material properties of the three-layer structure are presented based on the tensile test, the bending test and the friction test. Using the proposed method, we could visualize the stress distribution and wrinkles in the fabric-tying and elucidate its breaking condition. [ABSTRACT FROM AUTHOR]

Quantifying the stress distribution or finding mechanically coupled areas on the plate interface is fundamentally important for conjecturing megathrust earthquakes that may occur in the future. Kinematically coupled areas, or slip deficit distributions, on plate interfaces were commonly estimated by geodetic‐data analyses. However, mechanically coupled areas are not identical to the kinematically coupled areas. The present study develops an inversion method to estimate the stress rate distribution as mechanically coupled areas. We apply this method to the Nankai trough subduction zone, southwestern Japan to detect mechanically coupled areas. Some of the estimated coupled areas correspond to the rupture areas of historical earthquakes. Others are in a deeper part, which may release the stress as aseismic slip. We then construct a rupture scenario that can occur in the Nankai trough in the future based on the estimated mechanical coupling, assuming that an effective stress accumulation period is 100 years. The scenario consists of a foreshock of MW 8.0 followed by an afterslip of MW 7.7 and a mainshock of MW 8.2. Although the moment magnitude of the afterslip is slightly smaller than the foreshock, the strain energy released by the foreshock is significantly larger than the afterslip. In order to compare events when the stress drops are significantly different, it is useful to use the minimum released strain energy, or available energy, to characterize the magnitude of the events. Plain Language Summary: The driving force that generates huge earthquakes originates from the frictional locking between overriding continental plate and subducting oceanic plate. How strong and which parts are locked along the plate interface provide us with critical information for megathrust earthquakes that may occur in the future. Significantly coupled areas along the plate interface can be detected by the analysis of ground deformation. However, it is difficult to obtain correct information about the stress of the locking. To quantify the coupling along the plate interface, this study develops a method to estimate the stress rate based on elastic mechanics. We apply the method to the Nankai trough, in southwestern Japan, to estimate the plate locking. Then, by using the estimated locking information, we create a scenario for a sequence of earthquakes. This consists of a foreshock, a mainshock, and a slow slip between the foreshock and the mainshock. This study provides a method to obtain critical information about the mechanics on the plate boundary based on which we can create megathrust rupture scenarios. Key Points: An inversion method for the shear stress rate distribution along a plate boundary is developedMechanically coupled areas are identified on the plate interface in the Nankai troughA possible scenario for a megathrust earthquake after an afterslip of a foreshock is proposed based on the coupling distribution [ABSTRACT FROM AUTHOR]

Crustal stress is a crucial parameter for understanding tectonics and assessing the occurrence of large earthquakes. Stress at seismogenic depths over a wide area has been inferred from focal mechanism solutions. The existence of focal mechanism solutions determines the area that can be potentially studied. Therefore, we studied the crustal stress orientations in Japan from focal mechanism solutions of small earthquakes. First, we obtained about 220,000 focal mechanisms using the P‐wave first‐motion polarities picked by a deep learning model. Next, we performed a linearized inversion on the nationwide stress orientation model at a grid of 0.2‐degree intervals. The estimation errors reflect the quality and quantity of focal mechanism solutions. Overall, the results indicate that Japanese islands are under an east–west compressional stress, whereas some areas along the Pacific coast of northeast Japan are under east–west extensional stress. A closer look shows the spatial trends of stress orientation may vary near the geological borders, including the Hinagu and Futagawa faults in Kumamoto Prefecture (Kyushu Island) and the Median Tectonic Line in Shikoku Island. Our stress model also revealed the existence of stress anomalies around Cape Shionomisaki in the Kii peninsula. Most of the active faults are at approximately optimal orientation for the derived stress orientation and stress ratio, although uncertainties in the fault geometry, particularly the dip angle, substantially affect this evaluation. The stress map helps understand the overall vision of the crustal stress in Japan and further study the local stress distribution. Plain Language Summary: Stress, an internal force of the Earth, causes earthquakes and crustal deformation and forms characteristic landforms. Therefore, stress is a key to understanding the dynamics of the Earth. This study uses one of the features of earthquakes caused by crustal stress as an indicator. This feature is the "focal mechanism" corresponding to the orientation of the fault plane and slip direction on the fault. First, we derived numerous focal mechanism solutions for small earthquakes in Japan. The massive seismic waveform data processing was supported by a deep learning model we previously developed. The stress orientations consistent with the focal mechanism solutions were then estimated. The high‐resolution (about 20 km) nationwide stress map shows a general compression trend in the east–west direction, but in some spots around the Pacific coastal area of northeastern Japan, the compression trend is in the north‐south direction. In addition, it was found that the stress orientation changes along geological boundaries such as active faults and major tectonic lines. Furthermore, spots where the stress orientation differs from the surrounding area were identified. This stress map will be indispensable for future earthquake assessments and understanding of the formation mechanism of the Japanese islands. Key Points: We generated a nationwide crustal stress map with 0.2‐degree grids from focal mechanism solutions of about 220,000 microearthquakesWe observed a stress anomaly spot and stress orientation changes along geological borders, such as faults and tectonic linesMost of the active faults are almost optimally oriented to the estimated stress field [ABSTRACT FROM AUTHOR]

Cross‐correlation analysis was applied to long‐term onshore broadband records from April 2004 to March 2021 to detect and relocate shallow very low frequency earthquakes (VLFEs) southeast off the Kii Peninsula, along the Nankai Trough, Japan. We then determined the moment rate functions of detected shallow VLFEs using the Monte Carlo‐based simulated annealing method. According to this new comprehensive catalog, shallow VLFEs are widespread beneath the accretionary prism toe, but shallow VLFEs with large cumulative moments are localized around the western edge of the paleo‐Zenisu Ridge, which is subducted beneath southeast off the Kii Peninsula. Our results from the long‐term shallow VLFE catalog are well consistent with previous studies in this region, suggesting that heterogeneous structures and stress conditions due to the subducted paleo‐Zenisu Ridge promote the occurrence of shallow slow earthquakes. The relocated shallow VLFE epicenters illustrated three major episodes characterized by a similar activity area and five minor episodes characterized by different areas. The three major episodes exhibited slow frontal migration with different initiation locations, directions, and speeds, as well as several rapid reverse migrations. Episodes of minor activity were distributed in different locations within part of the area of major activity. Different patterns of shallow VLFE migration could reflect temporal changes in the pore‐fluid distribution or stress conditions of the plate boundary. Plain Language Summary: Our knowledge of the physical characteristics of shallow slow earthquakes, which may provide frictional properties on plate boundaries and preparation processes of large interplate earthquakes, is still limited. Thus, we comprehensively analyzed shallow very low frequency earthquakes (VLFEs) southeast off the Kii Peninsula, in the Nankai subduction zone, where large tsunamigenic earthquakes have repeatedly occurred with intervals of approximately 100–200 yr. We found that shallow VLFEs occurred around the western edge of the subducted oceanic ridge. We considered that this ridge causes complex stress and subsurface structures around the plate boundary and consequently promotes slow earthquake activity. Key Points: We estimated the locations and moment rate functions of shallow very low frequency earthquakes (VLFEs) that occurred near the Nankai TroughLarge cumulative moments of shallow VLFEs were concentrated in the region with the subducted oceanic ridgeThe migration of shallow VLFEs exhibits various patterns in terms of initiation, migration direction, and area [ABSTRACT FROM AUTHOR]

Aged conifer forests in Japan are expected to produce large-diameter logs, defined as logs with a top-end diameter of 30 cm or more. However, the knowledge and techniques for industrial processing of large-diameter logs of Japanese wood species have not been sufficiently developed. This study was aimed at characterizing the longitudinal component of residual stress distribution of large-diameter logs of sugi (Japanese cedar, Cryptomeria japonica), a major tree species cultivated in Japan, as the processing yield of primary lumber from large-diameter logs is affected by the magnitude and distribution pattern of the residual stress. The radial distributions of the released strain of residual stress, tensile Young's modulus, and residual stress were measured using 63 logs. The radial distributions of the released strain and residual stress showed typical patterns reported in previous studies: contraction near the bark and elongation near the pith in the released strain, tensile stress near the bark, and compressive stress near the pith. The radial distributions of Young's modulus showed a typical pattern: low near the pith and high near the bark. The difference between the maximum and minimum released strains in each log varied widely among individuals, which was expected to result in a wide variation in crooking when rip sawing. The longitudinal uniformity and axial symmetry of the radial distribution of the released strain and residual stress were experimentally confirmed, which lays the groundwork for improved understanding of the residual stress in sugi logs. [ABSTRACT FROM AUTHOR]

Background: Finite element analysis (FEA) has been previously applied for the biomechanical analysis of acetabular dysplasia and osteotomy. However, until now, there have been little reports on the use of FEA to evaluate the effects of pelvic tilt on stress distribution in the acetabulum.Methods: We used the Mechanical Finder Ver. 7.0 (RCCM, Inc., Japan) to construct finite element models based on 3D-CT data of patients, and designed dysplasia, borderline, and normal pelvic models. For analysis, body weight was placed on the sacrum and the load of the flexor muscles of the hip joint was placed on the ilium. The pelvic tilt was based on the anterior pelvic plane, and the pelvic tilt angles were -20°, 0°, and 20°. The load of the flexor muscle of the hip joint was calculated using the moment arm equation.Results: All three models showed the highest values of von Mises stress in the -20° pelvic tilt angle, and the lowest in the 20° angle. Stress distribution concentrated in the load-bearing area. The maximum values of von Mises stress in the borderline at pelvic tilt angles of -20° was 3.5Mpa, and in the dysplasia at pelvic tilt angles of 0° was 3.1Mpa.Conclusions: The pelvic tilt angle of -20° of the borderline model showed equal maximum values of von Mises stress than the dysplasia model of pelvic tilt angle of 0°, indicating that pelvic retroversion of -20° in borderline is a risk factor for osteoarthritis of the hip joints, similar to dysplasia. [ABSTRACT FROM AUTHOR]

This study presents a detailed reconstruction of the state of stress in the crust of the Japan Benioff zone that followed the Tohoku earthquake of March 11, 2011. The stress parameters were found using the method of cataclastic analysis applied to discontinuous displacements based on the identification of a homogeneous selection of earthquake mechanisms around a point of interest. The criteria used to make the selection rely on principles of plasticity theory as extended to cover the case of strain evolving in a cracked medium. The reconstruction used data on earthquake mechanisms from the NIED f-net catalog for the period of observation until June 1, 2018. An analysis of the patterns in the spatial stress distribution derived for six depth levels in the crust showed substantial changes in the state of stress observed in the aftershock area of the Tohoku earthquake in the upper lithospheric layers of the continental slope (0–30 km). The horizontal tensile stresses that appeared immediately after the earthquake are best observed in the uppermost crustal layer (0–10 km). As we go deeper into the earth, this state of stress becomes increasingly less representative. Estimates of the stress magnitudes based on a model of horizontal tension with pure shear showed that the change in the type of geodynamic regime in the upper crustal layer was accompanied by a large change in the level of shear stresses that are directed along the axis of the Benioff zone (the drop was about 90%) and a decrease in the level of maximum shear stresses by nearly 65% relative to its mean value. These results can be explained by a larger contribution into the change of the state of stress due to a quasi-homogeneous horizontal tension compared with that due to pure shear caused by the drop of tangential stresses in the Tohoku source. [ABSTRACT FROM AUTHOR]

This report shows packaging‐induced stress distribution of a small‐scale silicon chip encapsulated by a Small‐Outline Nonleaded package. The proposed method made it possible to visualize the stress distribution chart for a chip about 1.0 mm2 in size with high accuracy, even when the chip has only four pads. It is found that the stress was generated during resin molding, as determined from stress measurement during the middle of the packaging process. In addition, the impact of filler particle size and position in Epoxy Molding Compounds on the local stress of the chip surface is revealed. The compressive stresses were found to be greatest at the center of the chip and gradually decrease toward the edges. Also, the results for die pad structure produced a characteristic distribution chart in which the central area of the silicon chip has a smaller stress gradient. The impact of high‐temperature storage test on residual stress is also discussed. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Most of the seismicity in inland Kyushu, southwest Japan occur in the localized intraplate shear zones which are Beppu-Shimabara Graben (BSG) and left-lateral shear zone (LSZ). One of the largest fault systems in Japan (Median Tectonic Line—MTL), and subduction zone of the Philippine Sea Plate also exist near Kyushu. These suggest that the island arc, such as Kyushu has a complex deformation process. This study estimated the anelastic strain rate in the lower crust and the interplate coupling rate via inversion analysis using Global Navigation Satellite System data to elucidate the seismotectonics. Deformation in the lower crust and interplate coupling were modeled by cuboid volumetric sources and a back slip model, respectively. To stabilize the solution, a L2 regularization constraint was applied to the anelastic strain rate. Further, constraints on direction and smoothing to the slip deficit rate were applied. These strength of the constraints were determined via the minimum value of the Akaike Bayesian information criterion. The analyses showed that the anelastic strain rate of the BSG and LSZ was ∼0.6 ×10−6 yr−1, and BSG was related to MTL activity. The findings also suggest that this anelastic deformation in the lower crust created a stress concentration zone in the upper crust of BSG and LSZ, with a stress change rate of ∼6–10 kPa·yr−1. The value is consistent with the stress drop and recurrence interval of regional earthquakes, suggesting that the seismicity around BSG and LSZ is strongly influenced by anelastic deformation in the lower crust. It is also suggested that BSG and LSZ development is influenced by slab rollback, and a subducting ridge. Lastly, a comparison between the deviatoric stress field estimated using focal mechanisms and the anelastic strain rate suggests the existence of a shear zone consisting of weak faults south of BSG. • This study estimated the anelastic strain rate in the lower crust. • The anelastic strain rate in the lower crust of the BSG and LSZ was ∼0.6×10−6·yr−1. • Lower crust anelastic deformation creates stress concentration in the upper crust. • Plate geometry changes indirectly controls the anelastic deformation of island arc. [ABSTRACT FROM AUTHOR]

SUMMARY The Mw 9.0 off northeast Japan (Tohoku-oki) earthquake occurred on 2011 March 11 at the interface between the North American (NA) and Pacific (PA) plates. The occurrence of interplate earthquakes can be regarded as the sudden release of tectonic stress accumulated by the interseismic gradual increase of slip deficit in source regions. The inversion analysis of GPS velocity data for a seismically calm period (1996-2000) before the Tohoku-oki earthquake has revealed the existence of five remarkable slip-deficit zones distributed on the NA-PA plate interface along the southern Kuril-Japan trench. We analysed coseismic GPS displacement data for the Tohoku-oki earthquake with the same inversion method, and obtained the bimodal distribution of coseismic slip spreading over the southern two, Miyagi-oki and Fukushima-oki, interseismic slip-deficit zones. The maximum slip is 32 m for the Miyagi-oki slip-deficit zone but only 7 m for the Fukushima-oki slip-deficit zone. The extraordinarily large coseismic slip in the Miyagi-oki slip-deficit zone, where ordinarily large earthquakes with about 3 m coseismic slips have repeated every 40 yr in the past two centuries, suggests the total rupture of a 300-km-long basement asperity underlying much smaller-scale local asperities. [ABSTRACT FROM AUTHOR]

Abstract: We investigate spatial distribution of stress along the interplate boundary between Pacific and Okhotsk plates in Tohoku and Hokkaido regions, northern Japan from earthquake focal mechanisms compiled from the National Institute for Earth Science and Disaster Prevention (NIED) of Japan. The interplate boundary in this work is inferred as the surface defining the upper boundary of the double seismic zone (Benioff Zone). To investigate spatial variation in stress field we divide the interplate boundary into 20km×20km subfaults and estimate stress field in each subfault of 10km thickness. We find clear spatial variation in stress state along the subduction zone of the Pacific plate in northern Japan. Though most of the study area is characterized by trench normal uniaxial compression, in the Hidaka Collision Zone, the signature of collision between the Kurile and Japan arcs is evident in terms of radial compression. Distribution of the angle (ψ) between the maximum principal stress direction and the fault normal shows that the large subduction earthquakes have occurred in the region where this angle ψ varies between 30 and 45°. However in the case of recent M9.1, 2011 Tohoku-Oki earthquake, this correlation is not observed. We further investigate the frictional strength along the interplate boundary. Our results suggest: (1) The fault segments with ψ between 30 and 45° are frictionally strong (with friction coefficients between 0.6 and 0.8), (2) The fault segments with ψ between 45 and 62° are intermediately strong (with friction coefficients between 0.4 and 0.6), and (3) The fault segments with ψ above 62° are weak (with friction coefficients below 0.4). [Copyright &y& Elsevier]

The fitting of a stress trajectory pattern predicted by a 2D elastic model to an observed radial-parallel transitional dike pattern determines the orientation of far-field stress and pressure in the central magma chamber. We found such a transitional pattern in the Amakusa region, western Japan. On the other hand, the 3D dike orientations can be inverted using Bingham distributions to determine stress axes, stress ratios, and driving pressure ratios. From the Amakusa data, the 2D analysis indicated roughly N–S extensional far-field stress. The 3D analyses conducted in the parts of the dike swarm yielded horizontal maximum stress axes roughly parallel to the local stress orientations predicted by the 2D model. Subsets obtained in distant areas from the central magma chamber indicated a normal faulting stress regime with roughly N–S extension. So, both the 2D and 3D approaches led to consistent results. The 3D analyses indicated the declining frequency of the injection of highly overpressured magmas with distance from the chamber. Thus, we conclude the 3D analysis is useful to study dike swarms with transitional patterns. The paleostress determined from the Amakusa dikes suggests that the Shikoku basin subducted under Kyushu including the Amakusa region in the early middle Miocene. [Display omitted] • A dike swarm with a radial-parallel pattern transition was found in western Japan. • Stress trajectory predicted by a 2D elastic model was fitted very well to the pattern. • Stresses inverted from 3D dike orientations consistent with the trajectories. • Magma overpressure declined with distance from the central magma chamber. • The 3D stress inversion applied to the parts of radial dikes indicate local stresses. [ABSTRACT FROM AUTHOR]

The article reports on the factors that caused root fracture of endodontically treated teeth with a foundation restoration in Japan. It reveals the importance of minimal tooth grinding in the prevention of root fracture, and the association between the design of the foundation restoration without root fracture and the elimination of the fundamental restoration. It notes the need for dentists to create a suitable foundation restoration with enough retention.

Examines the applicability of an inversion method of identifying stress distribution to the Japanese Islands. Measurement of the deformation by the nationwide GPS array; Limitations of the inversion method when applied to the Japanese Islands.

A shear tab and high-strength bolts are often used to connect a steel H-beam to a column. The design demand and capacity of these elements vary from one standard to the other. To investigate the effect, this study applied a finite element method (FEM) to develop models for two steel moment connections and validated the effectiveness by test data. The connections were characteristic of bolted-web-and-welded-flange details. The FEM models were then used to study the design of shear tabs and high-strength bolts in accordance with the U.S. and Japan standards and compared to the Taiwan practice. The result showed a small difference in the peak loads of the connections. However, the U.S. direct welded flange connection had flange buckling and strength degradation at a relatively smaller drift. The connection had a thinner shear tab and fewer high-strength bolts. The other two connections had very similar design results and loading responses. The increase in shear-tab thickness reduced the stress concentration and fracture potential of the connections. It is, therefore, recommended to design a shear tab with moment capacity greater than the beam web. This will reduce the stress concentration of the base metal surrounding the beam-flange groove welds, increasing the connection ductility. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) pre-stack depth migrated seismic data are used to analyse the geometry and growth of shallow faults associated with tectonic shortening in four (4) prominent thrust anticlines off Nankai, SE Japan. The four thrust anticlines show a trenchward increase in horizontal shortening and deform the seafloor at present. They shortened the overburden strata by 7143 m in the Late Quaternary, reflecting a horizontal shortening of 32.9% in response to plate subduction. A significant number of closely spaced and segmented fault arrays is observed in their hinge regions. Vertically segmented fault arrays with local throw maxima between 5 and 14 m relate to the existence of more competent (strong) intervals, or layers. Incompetent (weak) intervals record relatively small throw values between 2 and 5 m. We show that the presence of closely spaced, segmented fault arrays at shallow stratigraphic levels can have a significant impact on local stress distribution, controlling near-seafloor strain in accretionary prisms as Nankai's. The observed mechanical layering is likely to continue at depth to control the accumulation of tectonic stress in faults posed to reactivate during seismic events. • Fault geometry responds to changes in lithology and mechanical stratigraphy. • Throw-depth plots indicate the strata affected by mechanical stratigraphy and fault growth. • Fault growth occurred in shallow parts of Nankai via segment linkage. • The impact of tectonic shortening is clear when considering distinct thrust anticlines. [ABSTRACT FROM AUTHOR]

• Database of 79 steel-encased precast concrete pile tests collected. • Bending capacity checked by stress distribution and strain compatibility methods. • Validated numerical model includes high-strength concrete and steel pipe buckling. • Model reproduces curvature, moment, drift and hysteresis behavior. • Effect of hollow core on concrete confinement, and buckling are important factors. The use of steel-encased precast concrete (SC) piles has risen rapidly for the construction of earthquake-resilient foundation systems for buildings in Japan and Southeast Asia. SC piles are used near the pile-pile cap connection owing to their increased ductility, and resistance against large bending moments and axial forces, compared to the other precast concrete piles. However, there are no official guidelines available for the design of SC piles in severe earthquakes, except for a proposed draft by the AIJ committee for the determination of bending capacities. In this work, a database of 79 tests on SC piles, all tested under axial-flexural loads, was created. The bending capacities obtained from these tests were used to verify the provisions of the proposed draft and the provisions for composite member design in AIJ, Eurocode 4 and, AISC. Furthermore, a distributed plasticity formulation was adopted to develop a non-linear static model, that takes into account the concrete confinement and local buckling of steel casing, for prediction of moment and drift capacities. The accuracy of the model was verified against various experiments, and the capability to reproduce the moment-drift relations was confirmed. [ABSTRACT FROM AUTHOR]

A long linear distribution of epicenters is seen along the Japan Sea coast in the San-in district located in southwestern Japan. This linear distribution of epicenters is called the seismic belt in the San-in district. The localization of intraplate earthquakes in the San-in district, far from plate boundaries, is not well understood. To answer this question, we look at the seismic velocity structure of the lower crust beneath the San-in district using seismic travel-time tomography. Our results show the existence of a low-velocity anomaly in the lower crust beneath the seismic belt. We infer that the deformation was concentrated in the low-velocity zone due to compressive stress caused by the subduction of oceanic plates, that stress concentration occurred just above the low-velocity zone, and that the seismic belt was therefore formed there. We also calculated the cutoff depths of shallow intraplate earthquakes in the San-in district. Based on the results, we consider the possible causes of the low-velocity anomaly in the lower crust beneath the seismic belt. We found that the cutoff depths of the intraplate earthquakes were shallower in the eastern part of the low-velocity zone in the lower crust beneath the seismic belt and deeper in the western part. Thus, the eastern part is likely to be hotter than the western part. We inferred that the eastern part was hot because a hot mantle upwelling approaches the Moho discontinuity below it and the resulting high temperature may be the main cause of the low-velocity anomaly. On the other hand, in the western part, we inferred that the temperature is not high because the mantle upwelling may not exist at shallow depth, and water dehydrated from the Philippine Sea plate reaches the lower crust, and the existence of this water may be the main cause of the low-velocity anomaly. [ABSTRACT FROM AUTHOR]

The model called "water-weakened lower crust model" has been proposed to explain the mechanism of stress concentration on faults causing inland earthquakes (Iio et al. 2002). According to this model, the viscosity of the deeper part of faults in the lower crust decreases by water, and stress concentrates on faults in the upper crust due to the localized deformation in the deeper part. Although this model has been reported to be qualitatively reasonable, we have not obtained a result indicating that the model is quantitatively reasonable. This is because we do not resolve a heterogeneous structure due to fluid in the deeper part of faults in the lower crust. In order to solve this problem, we try to image the heterogeneous structure in the lower crust in detail.As a method for imaging the heterogeneous structure in the lower crust, there is an S-wave reflection analysis (Aoki et al. 2016, Katoh et al. 2018). If the heterogeneous structure is related to fluid, seismic waves can be reflected there. Therefore, the heterogeneous structure due to fluid can be determined as a reflector. In this analysis, the resolution is extremely high, 1.5 km in the horizontal direction and 1 km in the vertical direction. Katoh et al. (2018) indicated that the reflector reflects that fluid exists in fractures generated by faulting from the positional relationship between the reflector, DLFs, and a fault zone, and they proposed the reflector was a fluid pathway. In the S-wave reflection analysis, it is difficult to determine the structure deeper than the reflector, therefore it is not resolved whether the reflector exists as a thin layer of the fluid pathway. For that reason, we estimated the structure beneath the reflector by calculating receiver functions using seismic waves incident on the reflector from below. In order to compare the result of the receiver function analysis with the result of S-wave reflection analysis, we used a same velocity structure in their analysis. As a result of the S-wave reflection analysis and the receiver function analysis, it is found that the reflector only exists on the north side of the Arima-Takatsuki fault zone (ATFZ), and it is found that reflector is a thin layer with low S-wave velocity. As the origin of the thin layer with low S-wave velocity, it is possible to consider fluid dehydrated from the Philippine Sea slab subducting beneath southwestern Japan and the ATFZ. In the vicinity of the ATFZ, it is known that fluid that seems to originate in the mantle spring out (Kazahaya et al. 2014). In the lower crust, pores between minerals exist independently (Yoshino et al. 2002), and fractures caused by faulting is thought to be necessary for fluid movement (Yoshino et al. 2002). Furthermore, since the spatial distribution of the reflector is related to the ATFZ, we consider that the reflector in the lower crust indicates that fluid exists in fractures caused by faulting. This result supports the water-weakened lower crust model. [ABSTRACT FROM AUTHOR]