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Topography results from the interplay between rock uplift and erosion, and studying river responses to active tectonics may enable the rates and spatial distribution of rock uplift to be inferred. Normalized channel steepness index (k sn) is widely used to infer rock uplift rates, and rock erodibility plays a significant role in determining the variation of channel steepness in response to external forces. Various measures may be applied to evaluate rock erodibility; however, since they are essentially qualitative, it is difficult to quantify relationships between rock mass strength and channel forms. In this study, we inferred long-term rock uplift rates along the Futagawa fault, an active normal-dextral fault, and the Idenokuchi fault, an active normal fault, in southwestern Japan, based on morphological characteristics of rivers across substrates with contrasting erodibility. The widely used detachment-limited model predicts that, when the rock uplift rate is spatially uniform, the ratio of erodibility of different rock types can be written by an inverse ratio of their k sn values. We employed this theoretical prediction to quantitatively calibrate the effects of rock mass strength on channel steepness. Within the study area, channel steepness was larger in the eastern part where volcanic rocks were exposed than in the western part where less resistant sedimentary rocks predominated. We calculated ratios of substrate erodibility using drainage basins close to the Futagawa fault that experienced similar rock uplift. Calibrated k sn exhibited a clear difference between the eastern and the western part of the fault, suggesting that contrasting erodibility alone cannot explain the observed channel steepness. We also confirmed that the observed channel steepness could not be explained without differential rock uplift, even when considering the combined effects of channel width, precipitation, and erosion process. The distribution of long-term rock uplift rates inferred from calibrated k sn and vertical slip rates of the fault compiled from published papers agree with the distribution of vertical displacement of the earthquake that occurred on the fault in 2016, suggesting that earthquakes similar to the 2016 event have occurred repeatedly in the study area. • We calibrated channel steepness based on the erodibility of substrate materials. • Spatial distribution of long-term uplift is inferred from bedrock river morphology. • Long-term uplift is similar to the vertical displacement of the 2016 earthquake. [ABSTRACT FROM AUTHOR]

Abstract: This paper focuses on the formation mechanism of fractures induced by excavation of a gallery in soft sedimentary rocks in the Horonobe area of Japan. Detailed fracture mapping of the gallery indicates that the fractures consist of both pre-existing shear fractures and excavation damaged zone (EDZ) fractures. EDZ fractures correspond to weak planes associated with bedding planes or transgranular cracks. The EDZ fractures terminate against pre-existing shear fractures. Therefore, even for excavations in soft sedimentary rocks, formation of the EDZ fractures are controlled by pre-existing fractures and earlier weak planes. [Copyright &y& Elsevier]

Abstract: The Japan Atomic Energy Agency (JAEA) has been implementing several research studies at the Horonobe Underground Research Laboratory (URL) in support of the Japanese R&D program for the geological disposal of High-Level Radioactive Waste (HLW). Understanding the development and properties of an EDZ (excavation disturbed or damaged zone), including the rock mechanical, hydrogeological and geochemical responses around excavated openings, is important to the design of plugs and sealing material and for performance assessment of geological disposal. The Mine-by Experiment described in this paper was carried out to investigate the development of an EDZ in one of the deep vertical shafts excavated in Neogene sedimentary rocks at the Horonobe URL site. The objective of this study is to obtain fundamental parameters of an EDZ in Neogene sedimentary rock, where case studies are few, in support of the geological disposal studies in Japan. Before and after shaft sinking, BTV (borehole television), borehole expansion tests, permeability tests and seismic velocity logging were carried out to determine initial conditions and changes in the mechanical and hydraulic properties. During shaft sinking, extensometers were installed in the rock mass to determine rock mass response to excavation. The variation of hydraulic properties was largest within one meter of the shaft wall and the variation in hydraulic conductivity was in the range of one order of magnitude. [Copyright &y& Elsevier]

Abstract: This paper describes the enrichment of hydrothermally altered volcanic and sedimentary rocks with arsenic (As) and lead (Pb), and the effects of pyrite and calcite on the mobilities and release mechanisms of these toxic elements under oxic and anoxic conditions. Enrichment of the altered rock with As and Pb predominantly occurred in precipitated pyrite grains and not on the alumino-silicate minerals making up the matrix of the rock. Arsenic was incorporated in pyrite grains formed during alteration in both volcanic and sedimentary rocks, but Pb was only found in the pyrite grains of the volcanic rock samples. When in contact with water, altered volcanic rocks had acidic pH while altered sedimentary rocks had alkaline pH. The mobilities of both As and Pb from the altered rocks were enhanced at acidic and alkaline pH and a minimum was observed in the circumneutral pH under both oxic and anoxic conditions. The absence of O2 retarded the oxidation of pyrite most notably in the alkaline region but not in the acidic and circumneutral pH. The absence of CO2 increased the pH of samples with significant calcite content but did not affect those containing substantial amounts of pyrite. Increasing the CO2 also had insignificant effect on the concentrations of As and Pb in the leachate. The mechanisms controlling the mobilization of As and Pb from these rocks like dissolution of soluble secondary minerals, pyrite oxidation and adsorption were all related to pyrite while the pH of the rock when in contact with water was controlled by pyrite and calcite. Thus, excavated waste rocks that have been altered can be grouped based on the relative abundance of pyrite and calcite and their pH when in contact with water. [Copyright &y& Elsevier]

Abstract: This paper focuses on the stress field that produced a fault system in the Horonobe area of Japan, and considers the relationship between the fault system and the rock mass response to shaft excavation in soft sedimentary rocks. In this area, hydraulic fracturing investigations in boreholes and tectonic plate movements indicate that the major horizontal principal stress is oriented E–W; however, during shaft excavation, the greatest convergence in the shaft was oriented NNE–SSW. Therefore, it is necessary to understand the influence of the fault system on the rock mass response to shaft excavation. We performed a fault-slip analysis of faults in the shaft wall and reconstructed the paleostress field that produced the fault system. The maximum horizontal principal stress was oriented mainly NNE–SSW, and the minimum horizontal principal stress was oriented mainly WNW–ESE. These directions are similar to the directions of maximum and minimum convergence in the shaft, respectively. The results show that a fault system can affect the rock mass response to shaft excavation in soft rock, and it is considered that the rock mass deformation is controlled by the fault system. In addition, it may be possible to assess and predict the rock mass behavior by focusing on paleostress field that produced the fault system. [Copyright &y& Elsevier]

Abstract: Earthquakes in active-folding zones often trigger long-lasting landform changes. Since an underground structure closely follows the motion of its surrounding soils and rocks even after it was damaged in an intense earthquake, experts in charge of reconstruction have to wait until they are convinced that the soils and rocks have been stabilized. Kizawa tunnel was seriously cracked during the 23 October 2004 Mid-Niigata Earthquake. The upper half of the tunnel''s cross-section near the north mouth shifted about 0.5m sideways. Since a ring-shaped cross-section of a tunnel sustains the surrounding soil pressure, this crack pattern seemed to be serious. The authors collaborated with the Nagaoka Regional Development Bureau, Niigata Prefectural Government, in investigating the causes of the damage and in conducting long-term observation of the soils and rocks. This paper summarizes some findings for rational rehabilitations through the investigations. [Copyright &y& Elsevier]

Abstract: This paper reports the results of laboratory and field experiments of CO2 sequestration into the Ogachi hot dry rock(HDR; the temperature is 200 degree C) site, where a part of CO2 will be expected to be fixed as carbonates by interaction with rocks (Georeactor; Ca extraction from rocks and carbonate fixation). In 2007, CO2 dissolved water (river water with dry ice) was directly injected into OGC-2 (from September 2nd to 9th) and Run #2(from September 11th to 16th). Several tracers were also injected at the same time. Water samples are collected at the depth of ca. 800 m by a sampler (500 ml in volume) and monitored for their chemical and isotopic compositions. During the Run #2 experiment, river water was injected into OGC-1 at 2 days after injection of CO2 water into OGC-2. During the field experiments, dissolution or precipitation rates of calcite were determined by using a technique of ”in site analyses”. Calcite crystals covered with Ti rod or Au film is hold in a crystal cell and set in a crystal sonde. The crystal sonde is then put into OGC-2 and water samples at the certain depth is introduced into the sonde. After 1 hour, the sonde is recovered and the calcite crystal is observed by a newly developed phase shift interferometer to analyze the dissolution or precipitation rates of calcite from the reservoir fluids. The “in situ analyses” show that calcite precipitation was observed within 2 day after the injection. This supports the view that most of CO2 injected might be fixed as carbonate. [Copyright &y& Elsevier]

Abstract: To construct an investigation guideline, RITE estimated storage capacities of CO2 in deep saline aquifers in sedimentary rocks inland and offshore Japan. This paper proposes a method to quantitatively and qualitatively assess geological data available from seismic, gravity and borehole investigations. By technically evaluating aquifer volume and storage and sealing effectiveness, the accuracy of calculated storage potential is examined. It seems capable of increasing estimation accuracy, provided the geological data are carefully examined. This method may be used as a stepping-stone for evaluation methods to be used in the investigations for future site selection of pilot and actual operation plants. [Copyright &y& Elsevier]

Abstract: It is difficult to apply stress inversion to fault-slip data obtained from highly tilted sedimentary layers, especially in areas where criteria for fault sorting are not available at outcrops. This paper shows that a bedding tilt test similar to that used in paleomagnetism allows paleostresses to be inferred. In order to assess its validity, the testing method was applied firstly to artificial fault-slip data generated with a hypothetical history for folding and faulting with known paleostresses. The stresses were successfully recovered and the correct timing of faulting relative to tilting could be determined. The test procedure was secondly applied to mesoscale faults observed in a mid-Pleistocene sedimentary unit in central Japan, which was folded in late Pleistocene. It was found that the majority of the faults were activated mainly by a strike-slip faulting regime of stress at the middle stage of folding. [Copyright &y& Elsevier]

The authors introduce a case study of research on the provenance of radiolaria-bearing gravels and clasts of the monomictic chert-pebble conglomerates in the Lower Cretaceous Monobegawa Group, a paralic molasse in the Outer Zone of Southwest Japan. Reconstruction of oceanic plate stratigraphy from gravels and clasts in monomictic chert-pebble conglomerates based on their lithology and radiolarian ages is possible and effective for the provenance research in the case of the Monobegawa Group. A review of provenance studies of radiolaria-bearing gravels in Mesozoic orogenic sediments in SW Japan and Korea is included. The paper concludes with the discussion of the erosional events of the Jurassic and pre-Jurassic accretionary complexes in SW Japan with reference to the Late Mesozoic geological history in the eastern margin of Asian continent. [Copyright &y& Elsevier]

The middle–late Miocene siliceous mudstones and siltstones of the Akita and Aomori regions in Northern Honshu, Japan, provide an excellent geological record of the paleoenvironment of the Japan Sea. In this paper, we present results of sedimentological and geochemical analyses of the Akaishi and Odoji Formations from the Tsugaru Basin in the Aomori region and of the Onnagawa Formation from the Sugisawa area in the Akita region. Lithofacies descriptions, geochemical compositions (including major elements, total organic carbon [TOC], total nitrogen [TN], and total sulfur [TS]), and petrographic observations of the framboidal pyrite were used to investigate the origin of the detrital fraction, the paleoproductivity, and the paleoredox conditions of the bottom waters in the Japan Sea. Moreover, through interpretation of these data, the relationship between organic carbon preservation and the paleoenvironmental evolution was clarified. The data indicate that paleoweathering was moderate to high in the detrital fraction source terrain; the detrital fraction originated from a felsic source and was probably transported from Asia to the Japan Sea by monsoons and from the Japanese islands by riverine input; the high concentrations of biogenic SiO 2 indicate high primary productivity in the surface water, probably induced by intense upwelling of nutrients; the Tsugaru Basin area was characterized by oxygenated bottom water, whereas the Sugisawa area was characterized by oxygenated to low-oxygenated bottom water based on the lithofacies variation and the size of the framboidal pyrite; and the organic carbon accumulation in the Odoji and Onnagawa Formations was mainly controlled by paleoproductivity and dilution from the detrital fraction rather than the paleoredox conditions. Alternatively, the organic carbon accumulation in the Akaishi Formation was likely controlled by the paleoredox conditions. • We studied the paleoenvironment of the Japan Sea during the middle-late Miocene. • Warm-humid climate and medium-high chemical weathering prevailed at detrital source. • Basin geometry and paleodepth influenced the paleo-oxygenation of bottom waters. • Asian monsoon and continental input from Japan influenced the detrital fraction. • The detritus enhanced the preservation of TOC in dysoxic intervals. [ABSTRACT FROM AUTHOR]

Abstract: The Japan Atomic Energy Agency has been developing the Horonobe Underground Research Laboratory in sedimentary rock at Horonobe, on Hokkaido, Japan, as part of the research and development program on geological disposal of high-level radioactive waste. Fundamental parts of the geological and hydrogeological investigations in the project include BHTV and EMI logging, fluid logging, pressure build-up tests and hydraulic packer tests in eleven 470-m to 1020-m deep boreholes, supplemented by laboratory permeability tests on core samples from the sedimentary formations. The results show that hydraulic conductivity varies significantly and that fractures/faults have a close relationship to the heterogeneities in hydraulic conductivity. This paper discusses the heterogeneities in hydraulic conductivity from the perspective of scale effect, to characterize and model the hydrogeological environment. It was determined from the relationship between hydraulic conductivities and test interval lengths that the heterogeneity of hydraulic conductivity in the Wakkanai Formation decreased with increase of test interval length. Considering this observation, the following concept for hydrogeological modeling dependent on the scale is proposed; the Wakkanai Formation should be modeled as a fractured medium at scales ranging from 10-m to 200-m and as a homogeneous medium at scales over 200-m. The Koetoi Formation, the other formation of interest and the intact rock in both formations could be modeled as homogeneous media. [Copyright &y& Elsevier]