Language：Japanese   Publisher：The Geological Society of Japan  

<p>We developed a new portable percussion piston corer for coring lacustrine and shallow-marine sediments from a frozen ice surface. The weight of the corer is less than 100 kg, and it can be separated into individual components. Therefore, the corer can be carried to remote sites using pack frames and allows coring to be undertaken in areas that cannot be reached with mechanical drilling equipment. The engine-driven percussion coring can obtain relatively coarse and hard sediments. The main body of the corer is composed of a transparent polycarbonate pipe with an external diameter of 76 mm, which allows us to check length and facies of the cored sediments immediately after coring. The polycarbonate pipe is suitable for preserving sediments and can be easily replaced in subsequent coring. The new corer is advantageous for lacustrine- and marine-sediment coring in extreme (cold) environments, such as Antarctica and high mountains, and may also be applied to a wide range of geoscientific fields.</p>

DOI： 10.5575/geosoc.2018.0065

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Language：Japanese   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2019.0_157

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Deep-seated gravitational slope deformation (DSGSD) is a largely unnoticed but important long-term mass wasting process that may result in catastrophic failure of mountain slopes. Manifested by small topographic irregularities such as ridge-parallel scarps and linear depressions, it has been predominantly reported in alpine landscapes above timber lines. On the basis of area-wide high-resolution topographic data acquired by light detection and ranging (lidar) surveys, we here show that similar to 96% of existing gravitational scarps have been hidden under forest canopies in the Etsumi Mountains, central Japan. The scarps are surprisingly widespread over the mountains with a mean line density of as large as 0.87km/km(2). Our analyses of the scarp distribution suggest that uphill-facing scarps are primary geomorphic signals of DSGSD with a destabilized rock mass larger than similar to 10(5)m(2), whereas downhill-facing scarps principally occur in response to more localized slope deformation. In terms of controls, topography is by far the most influential factor in triggering and promoting DSGSD. Despite the M 7.5 earthquake in 1891, impact of large local earthquakes proves to be not very strong. Comparison with preexisting landslide maps further suggests that DSGSD and large-scale landslides are not different slope processes but represent different stages of the same process. Our results highlight limitations of aerial-photograph interpretation in forest-covered mountains and the need for lidar-assisted mapping for deeper understanding of this long-term process and interactions between surface and tectonic processes.

DOI： 10.1002/2017JF004382

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

In order to mitigate landslide risks, monitoring of ground water is essential. Previous indoor experiments suggest that the self-potential approach has an advantage to establish the early warning system in performance to detect related signals and in cost. To evaluate results obtained from the previous indoor experiments, in situ measurements are required. To achieve this, we selected a test slope at Nishiikawa, Tokushima, Japan and we performed preliminary electrical resistivity exploration (ERT) and core-sampling. The results of ERT show that there are low resistive areas in shallow depth (&lt;3 m). The core-sampling results also indicate that there exists the structure which corresponds to slip surface. In addition, anisotropy in magnetic susceptibility was examined and the samples around the estimated slip surface region provide the oblate ellipsoid characteristics. These results of ERT and core analyses are consistent and make convince the identification of the slip surface. Based on these preliminary results, we set up the in situ self-potential observation at the slope and started measurements.

DOI： 10.1002/ecj.11967

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Language：Japanese   Publisher：Tokyo Geographical Society  

<p> Unmanned aerial vehicle-based "Structure from Motion" (UAV-SfM) photogrammetry is becoming increasingly important for obtaining high-definition topographic data in a variety of earth science research. Antarctica is one of the best fields in which UAV-SfM surveys are applied, because detailed geomorphological data are essential for reconstructing past Antarctic ice sheet changes and understanding landform evolution processes in a hyper-arid and hypothermal environment. However, application of UAVs in Antarctica has been limited because of difficulties arising from low temperatures and the restricted availability of the Global Navigation Satellite System (GNSS)-assisted navigation system at high latitudes. In this article, we provide methodological solutions for these difficulties, and report several preliminary results of UAV surveys in central Dronning Maud Land and the Soya Coast in East Antarctica. A digital elevation model (DEM) obtained in central Dronning Maud Land clearly shows 3D structures of polygons developed on glacial tills. At the Soya Coast, a DEM analysis reveals detailed geomorphological characteristics, such as moraine ridges originating from a former ice stream and differential erosion of the basement due to weathering. Based on these results, we suggest that the UAV survey has certain merits for conducting an efficient field survey in the extremely large areas of Antarctica within a limited time, and has great potential for reconstructing past Antarctic ice sheet changes and obtaining a further understanding of landform evolution processes.</p>

DOI： 10.5026/jgeography.126.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

An ENE-trending similar to 30-km-long surface rupture emerged during the Mw = 7.0 16 April 2016 Kumamoto earthquake along the previously mapped Futagawa and northern Hinagu faults. This included a previously unknown 5-km-long fault within the Aso Caldera, central Kyushu. The rupture zone is mostly composed of right-lateral slip sections, with a maximum of 2-m coseismic slip. One of the noteworthy features we observed in the field are similar to 10-km-long segmented normal fault scarps, dipping to the northwest, along the previously mapped Idenokuchi fault, 1.2-2.0 km south of and subparallel to the Futagawa fault. The maximum amount of coseismic throw on the Idenokuchi fault is similar to 2 m, which is nearly equivalent to the maximum slip on the strike-slip rupture. The locations and slip motions of the 2016 rupture are also manifested as interferogram fringe offsets in InSAR images. Together with geodetic and seismic inversions of subsurface fault slip, we present a schematic structural model where oblique motion occurred on a northwest-dipping subsurface fault and the slip is partitioned at the surface into strike-slip and normal fault scarps. Our simple dislocation model demonstrates that this bifurcation into pure strike-slip and normal faults likely occurs for optimally oriented failure near the surface. The Kumamoto case, with detailed geological observations and geophysical models, would be the second significant slip-partitioned earthquake around the globe. It provides an important insight into scale-and depth-dependent stress heterogeneity and an implication to a proper estimate of seismic hazard in complex and broad multiple fault strands.

DOI： 10.1186/s40623-016-0560-8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The Kanto Basin, the largest lowland in Japan, developed by flexure as a result of (1) the subduction of the Philippine Sea (PHS) and the Pacific (PAC) plates and (2) the repeated collision of the Izu-Bonin arc fragments with the Japanese island arc. Geomorphological, geological, and thermochronological data on vertical movements over the last 1 My suggest that subsidence initially affected the entire basin after which the area of subsidence gradually narrowed until, finally, the basin began to experience uplift. In this study, we modeled the tectonic evolution of the Kanto Basin following the method of Matsu'ura and Sato (1989) for a kinematic subduction model with dislocations, in order to quantitatively assess the effects of PHS and PAC subduction. We include the steady slip-rate deficit (permanent locking rate at the plate interface) in our model to account for collision process. We explore how the latest collision of the Izu Peninsula block has been affected by a westerly shift in the PHS plate motion vector with respect to the Eurasian plate, thought to have occurred between 1.0-0.5 Ma, using long-term vertical deformation data to constrain extent of the locked zone on the plate interface. We evaluated the change in vertical deformation rate for two scenarios: (1) a synchronous shift in the orientation of the locked zone as PHS plate motion shifts and (2) a delayed shift in the orientation of the locked zone following the shift in plate motion. Observed changes in the uplift/subsidence pattern are better explained by scenario (2), suggesting that recent (&lt;1 My) deformation in the Kanto Basin shows a lag in crustal response to the plate motion shift. We also calculated stress accumulation rates and found a good match with observed earthquake mechanisms, which shows that intraplate earthquakes serve to release stress accumulated through long-term plate interactions. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2016.04.005

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：National Institute of Polar Research  

Geomorphologic and geologic field surveys were conducted in central Dronning Maud Land during the summer of 2015-2016 as part of the 57th Japanese Antarctic Research Expedition (JARE-57). The members of the field expedition included three geomorphologists, a geologist, and a field assistant. This field expedition was fully supported by the Norwegian Polar Institute (NPI) and the South African National Antarctic Program (SANAP), and it was the first JARE expedition to use the Troll and SANAE stations. The NPI provided airborne access from Germany (Norway, on the way back) to the Troll station in central Dronning Maud Land via Cape Town, South Africa. The SANAP provided a helicopter to access nunataks and mountains in this area from the Troll and SANAE stations. This report summarizes the activities of this field expedition including fieldwork, logistics, and weather observations.

Scopus

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER INT PUBLISHING AG  

Small-scale geomorphic features of sagging have been known to occur in mountainous areas in Japan by the analyses of high resolution map images made from the LiDAR data. Development histories of the sagging landforms were analyzed by the GIS analyses, field mapping, machine and hand auger boring, AMS C-14 dating, and tephra geochronology in the Mt. Kanmuriyama, Tsuenomine and Nogo-Hakusan areas. Sediments accumulated in the ridge-top depression in the Mt. Kanmuriyama area yield wood fragments with the ages of 1,234-1060, 6,191-5,996 and 7,931-7,731 cal BP, and also include the K-Ah tephra of ca 7.3 ka. These ages indicate that the depression started to form at the beginning of warm and humid climate after the last glacial period. On the other hand, the double ridges in the Mt. Tsuenomine area formed much earlier before the deposition of the Kikai-Tozurahara tephra about 95 ka. The GIS analyses of sagging in the Mt. Nogo-Hakusan area indicate that most of them are distributed on the flat or gentle surface just above the knick line (erosion front); it means that the knick lines retreat through the repetitive formation and destruction of the sagging landforms.

DOI： 10.1007/978-3-319-09057-3_91

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Language：Japanese   Publisher：Japanese Society for Active Fault Studies  

<p>The 2014 M 6.7 Naganoken-hokubu earthquake was caused by movement of the Kamishiro fault located in the northernmost part of the Itoigawa-Shizuoka Tectonic Line (ISTL) active fault system, central Japan. We conducted a series of field research immediately after the earthquake to describe coseismic surface ruptures. Our description methods were: 1) field reconnaissance using pre- and post-earthquake airphotos; 2) quick measurement using staff; 3) topographic profiling using Auto Level and Total Station; and, 4) UAV and highpole SfM measurement. We identified 9-km-long coseismic surface rupture, most of which was located along the pre-existing surface trace of the Kamishiro fault. The maximum value of coseismic vertical offset was ca. 1 m or more, which was recorded at Oide in the northern part of the rupture. Based on comparison of the 2014 coseismic slip distribution with the long-term slip rate distribution, both 2014 slip amount and cumulative offset amounts of L2 and L3 terrace surfaces are larger in the northern end of the ruptures. This implies that the subsurface coseismic slip during pre-2014 earthquakes continued toward the north, similar to that during the 2014 earthquake. In addition, both coseismic slip and long-term slip rate becomes smaller toward the south, indicating that the Kamishiro area is one of the segment boundaries in the northern part of the ISTL active fault system. Further investigations of the 2014 earthquake and the Kamishiro fault are needed to understand formation of tectonic landforms, landscape development, or earthquake prediction model of active faults.</p>

DOI： 10.11462/afr.2015.43_149

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Despite successes elsewhere in the world, 2 m resolution DEMs from a standard airborne LiDAR survey failed to detect small tectonic-geomorphic features in densely-forested high-relief mountains of central Japan. Our new 0.5-m DEMs from an unprecedentedly high-resolution LiDAR survey along the Neodani Fault now reveal a number of previously unknown fault scarps as well as other hidden geomorphic features. The survey achieves a ground-return density of 6.2 m(-2) out of a total shot density of as much as similar to 12.7 m(-2). The main factor to gain sufficient ground returns in unfavorable conditions is a large side lap of similar to 70% between flight swaths, which means that any specific area in the target zone is scanned three or more times from different angles. Evaluation of DEMs with resolution from 0.25 to 10 m assures that a 0.5m resolution LiDAR DEM is necessary for the detection of subtle tectonic breaks. Another key factor for complete detection of small tectonic-geomorphic features is the application of a recently developed DEM visualization "Red Relief Image Map (RRIM)", which allows mapping of all the small features with various sizes, orientations and morphology, overcoming major drawbacks of classic DEM visualizations. A very high-resolution LiDAR survey aided with RRIM visualization as used in this study provides a more reliable approach for the detailed mapping of slight active fault traces hidden under dense vegetation. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.geomorph.2012.11.001

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

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Language：Japanese   Publisher：SEISMOLOGICAL SOCIETY OF JAPAN  

The M_jma 7.2 (M_w 6.9) Iwate-Miyagi Nairiku earthquake struck mountainous regions east of volcanic front in northern Honshu. To understand the relation between coseismic surface deformation and the seismogenic faulting and to have lessons in the long-term earthquake forecasting, we have performed urgent field investigations immediately after the main shock, while fragile structure and surface geomorphic features were fresh. More than 13 fault-rupture observations suggest that the estimated total length of the tectonic ground breakages reaches &sim;20 km even though their locations are spotty rather than continuous along the entire trend. Contractional features such as thrust fault exposures, flexure, tilting, and buckling deformations predominate on the rupture zone, which is consistent with the reverse faulting under the WNW-ESE compressional stress field in northern Honshu. Such shortening features as well as vertical displacements were visible on cultural features such as concrete, asphalt paved roads, sidewalks, guardrails, drainage ditches, and rice paddies. Amounts of vertical offset and horizontal shortening measured using such cultural piercing points are mostly smaller than 50 cm (&sim;1 m of net slip). Fractures with such small slip, in turn, would not have been noticeable and may reflect the spotty distribution of the ruptures. Meanwhile, near the southern end of the rupture zone, fault structure and slip sense become complex and measured offsets are exceptionally large. We found a E-W-striking &sim;1-km-long continuous rupture involved with 4-to-8-m dextral and 2-to-4-m vertical offsets of a paved road, trails, and rills near a massive giant landslide at the northern rim of the Aratozawa dam reservoir. Terrestrial LiDAR (Light Detection and Ranging) measurements together with our field observations reveal typical features of strike-slip faulting such as mole tracks, fissures, pressure ridges, bulges, and shutter ridges as well as the offset rills and ridges. Detail mapping of the ruptures suggests that this strike-slip dominant fault is a lateral ramp or tear fault that connects two distinct NNE-trending thrust faults, although we cannot rule out the possibility of a large mass movement due to gravitational force to induce such large displacements without suffcient geodetic and geologic data. The mapped zone of the ruptures approximately locates along the central part of the surface projection of a &sim;40-km-long west-dipping source fault and associated aftershock zone. It also well corresponds to an asperity estimated from seismic and geodetic inversions, particularly southern end of the ground breakage zone. However, from the viewpoint of the long-term predictability, the surface fracturing occurred where none of active faults was previously mapped. Although several active geomorphic strands are likely to have reoccupied with the 2008 event, they are more spotty than the 2008 ruptures. Thus it would not have allowed us to properly evaluate size of the shock and entire extension of the rupture.

DOI： 10.4294/zisin.62.153

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SEISMOLOGICAL SOC AMER  

During the 1992 M-w 7.3 Landers earthquake in the eastern California shear zone, only the shallowest part of the central 8 km of the Camp Rock fault apparently ruptured, triggered by coseismic static stress changes. Our detailed tectonic-geomorphic analysis of a 2 km long stretch of the central Camp Rock fault reveals that the 1992 triggered surface rupture differs markedly from earlier primary surface ruptures in terms of its vertical-slip function. We interpret this to be related to a difference in stress directions that induced fault slips: the 1992 static stress changes decreased normal stress on the central Camp Rock fault, thereby inducing a normal component of slip, whereas a minor reverse-slip component is associated with more typical primary seismogenic surface ruptures due to regional north-south compression. Our findings suggest that a detailed geomorphic analysis of a key locality may allow for isolation of triggered surface ruptures from repeated primary surface ruptures identified in paleoseismic studies.

DOI： 10.1785/0120080310

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SEISMOLOGICAL SOC AMER  

Multiple faults with different paleoseismic histories sometimes rupture simultaneously, resulting in a larger earthquake than expected. To test behavioral models for a fault involved in a multiple-fault rupture, we performed detailed tectonic-geomorphological mapping along the Neodani fault, central Japan, one of several faults that ruptured simultaneously during the devastating 1891 M-w 7.5 Nobi earthquake. Our mapping showed that the along-strike distributions of the long-term rates of left-lateral and vertical slips generally mimic in shape those of the 1891 slip, implying that the slip-patch behavior, in which smaller more frequent earthquake ruptures fill in low-slip portions of the 1891 rupture, does not apply to the Neodani fault. If the earthquake recurrence interval estimated from a previous paleoseismic trench is correct, however, the Neodani fault should not be characterized by repetition of same slip-function earthquake ruptures or the characteristic slip-function behavior. The observations can instead be explained by the semicharacteristic slip-function behavior, in which a similarly shaped slip distribution is repeated independently of the rupture of adjacent faults, but the amount of slip varies. Nonetheless, characteristic slip-function behavior may still be a valid interpretation if some of the paleoseismic events identified in the trench are minor sympathetic-slip events. Although we found that the shape of the slip distribution has been quite stable through successive earthquakes, including a multiple-fault rupture earthquake, further paleoseismic efforts are warranted to examine the stability in the amount of slip.

DOI： 10.1785/0120070204

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：GEOLOGICAL SOC AMER, INC  

The 2005 Kashmir earthquake in Pakistan occurred on a previously mapped active fault around the northwest margin of the Indo-Asian collision zone. To address the quantitative contribution of the earthquake to plate convergence, we performed paleoseismological trench excavations at Nisar Camp site near Muzaffarabad across the middle section of the 2005 surface rupture. The fault strands exposed in the trench cut late Holocene fluvial deposits and record evidence of both the 2005 and a penultimate event, supported by the presence of colluvial deposits and a downdip increase in displacement along the fault strands. The 2005 event produced a net slip of 5.4 m, and the penultimate earthquake exhibits a similar amount of slip. Radiocarbon ages and historical accounts loosely constrain the timing of the penultimate event between 500 and 2200 yr B.P.; however, the exposed section encompasses similar to 4 k.y. of stratigraphy, suggesting an average interevent interval of similar to 2 k.y. for the 2005 type events. We thus conclude that the 2005 event did not occur on the plate boundary megathrusts, but on intraplate active faults within the Sub-Himalaya. Consequently, the accumulated elastic strain around the complex northwestern margin of the Indo-Asian collision zone has not been significantly released by the 2005 earthquake.

DOI： 10.1130/G25028A.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Closely spaced sediment slices and cores reveal evidence for recurrent folding in the past 18 ka across the tip of a blind thrust fault near Kyoto, central Japan. The slices, 0.4 m wide and up to 5.5 m long, collected with "geoslicer'' technique, exposed the central 100 m of a stratigraphic cross section that extends across a fold scarp in the southern Biwako-seigan fault zone. A chronology inferred with 109 radiocarbon ages suggests that the most recent blind thrust earthquake occurred in the range A. D. 1060-1260, most likely around A. D. 1170. Historical accounts strongly support that this earthquake correlates with the 1185 M 7.4 Genryaku Kyoto earthquake. The earthquake produced a broad surficial fold more than 200 m wide with a vertical displacement of 3 m or more. Earlier paleoearthquakes lack well-defined event horizons, but we find that the deformation of the 18-ka unit is likely 4 times that from the most recent earthquake. Our results show the application of geoslicer technique to blind thrust paleoseismology, for which traditional trenching is rarely applicable or useful because of broad surficial deformation and commonly shallow groundwater at potential paleoseismic sites.

DOI： 10.1029/2007JB005300

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SEISMOLOGICAL SOC AMER  

To provide a detailed record of a relatively rare thrust surface rupture and examine its active tectonic implications, we have conducted field mapping of the surface rupture associated with the 2005 M-w 7.6 Kashmir earthquake. Despite the difficulty arising from massive earthquake-induced landslides along the surface rupture, we found that typical pressure ridges and warps extend northwestward for a distance of similar to 70 km, with a northeast-side-up vertical separation of up to similar to 7 m. Neither the main frontal thrust nor the main boundary thrust is responsible for the earthquake, but three active faults or fault segments within the Sub-Himalaya, collectively called the Balakot-Bagh fault, compose the causative fault. Although the fault exhibits substantial geomorphic expression of repeated similar surface ruptures, only a part of it had been mapped as active before the earthquake. The location of the hypocenter suggests that the rupture was initiated at a deep portion of the northern-central segment boundary and propagated bilaterally to eventually break all three segments. Our obtained surface rupture traces and the along-strike-slip distribution are both in good agreement with results of prompt analyses of satellite images, indicating that space geodesy can greatly aid in time-consuming field mapping of surface ruptures. Assuming that the extensive fill terrace in the meizoseismal area was abandoned during 10 30 ka, we tentatively estimate the earthquake recurrence interval and shortening rate on the Balakot-Bagh fault to be 1000-3300 yr and 1:4-4:1 mm/yr, respectively. These estimates indicate that the Balakot-Bagh fault is not a main player of Himalayan contraction accommodation.. Selected field photographs and ArcGIS files of the mapped surface rupture traces and measured vertical separations are available in the electronic edition of BSSA.

DOI： 10.1785/0120070073

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TERRA SCIENTIFIC PUBL CO  

At least 300 tons of subrounded to well-rounded wood blocks emerged onto the seafloor at a water depth of 70-100 m during the 2007 M(w) 6.6 Chuetsu-oki, central Japan, earthquake. Radiocarbon dating and taxonomic identification of eight of those wood blocks suggest that they were transported from inland during the middle to late Holocene, buried by Subsequent sedimentation, and brought up onto the seafloor in 2007, most likely by submarine liquefaction induced by strong shaking. In particular, all eight blocks gave ages older than 2500 cal yr BP, implying the possibility that the 2007 earthquake was the first earthquake during the last two millennia to have caused shaking strong enough to induce submarine liquefaction in the 2007 meizoseismal area. However, we cannot rule out the possibility of multiple large earthquakes after approximately 2 ka, if the buried wood sources cannot be emptied by a single earthquake. Further studies are required to examine paleoseismic implications of the emergence of these wood blocks in 2007.

DOI： 10.1186/BF03353152

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TERRA SCIENTIFIC PUBL CO  

The March 25. 2007 Noto Hanto earthquake (M(j) = 6.9, M(w) = 6.7) generated vertical crustal movement along the northwestern coast of the Noto Peninsula, Central Japan. Soon after the event, we estimated the pattern and amount of coseismic coastal movement based on uplifted and subsided intertidal sessile organisms. Our observations reveal a broad 20-km-wide asymmetric zone of surficial deformation above and across the south-dipping source fault, with it steep north-facing frontal limb and a gentle south-facing back limb. The maximum coseismic Uplift was approximately 40 cm at the crest of the zone of deformation. The result of forward modeling suggests that the top of the south-dipping source fault is buried at a depth of approximately 2 km, and that 1.2 m of slip on the fault provides the best fit to our surface observations. Our results demonstrate that traditional field investigations should be combined with modern instrumental observations such as GPS and InSAR to obtain the most effective and reliable spatio-temporal estimates of crustal movement associated with large earthquakes.

DOI： 10.1186/BF03352869

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

In this study we utilize marine shell samples from two levels of historically uplifted sessile mollusk assemblages and raised wave-cut benches to evaluate the marine reservoir correction (Delta R) for the Pacific coast of central Japan. Elevation measurements of the uplifted marine shells indicate that the lower assemblage emerged during the 1923 Taisho Kanto earthquake (M7.9), whereas uplift of the upper assemblage is most likely but less confidently ascribed to the 1703 Genroku Kanto earthquake (M8.2). Radiocarbon dating of carefully selected samples from the upper and lower assemblages yielded very similar Delta R values of 82 +/- 33 and 77 +/- 32 yr, respectively. We regard the former Delta R value as a representative and more reliable value given the uncertainty in correlation of the upper assemblage with the 1703 earthquake. This result is consistent with previously reported Delta R values for the Pacific coast of south-central Japan and areas around the Sea of Japan that are influenced by warm ocean currents. Radiocarbon dating of coseismically uplifted shells can aid in estimating marine reservoir ages in the tectonically active Japan Islands. (c) 2006 University of Washington. All rights reserved.

DOI： 10.1016/j.yqres.2006.09.003

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Language：Japanese   Publisher：Japanese Society for Active Fault Studies  

The Yugamine fault,10 km in length, is in the north-central part of the Atera fault zone. We studied Holocene activity of the Yugamine fault through a trenching survey. We excavated a trench across the scarplet on the L 1 terrace at Obayashi district. Some humic layers and fluvial gravels are exposed on the trench walls. The Yugamine fault has cut through these layers to form a linear depression on its NE side. From the structural evidence along the fault plane and angular unconformity, we recognize at least four faulting events in this trench.

DOI： 10.11462/afr1985.2007.27_201

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Language：Japanese   Publisher：Tokyo Geographical Society  

Excavating a pit across a small up-hill facing fault scarp on a mountain slope could be a paleoseismological tool for intramontane active faults, which usually lack suitable sites for traditional trenching. We tested this method on the Daguchi fault, north of Lake Biwa, southwest Japan, a typical short strike-slip fault in a mountainous region. Our test excavation at the Kurokoyama site on the southern subsegment of the fault, together with a re-interpretation of our previous excavation at the Daguchi site on the northern subsegment, allow us to obtain some constraints on the surface-faulting history of the fault. The timing of the most recent event is estimated to be 450-1050 cal. y.B.P. (900-1500 A.D.), whereas that of the penultimate event is poorly constrained : 1500-7300 cal. y.B.P. or prior to 5000-7300 cal. y.B.P., depending on different interpretations of the infilled fissure exposed on the pit wall. For either interpretation, our result is consistent with estimates from a previous paleoseismic study by Sugiyama and Yoshioka (1999), but the presence of other stratigraphically unidentifiable events cannot be ruled out, given the lack of piecing layers across the main fault in our pits, as well as their trench. The principal reason for the poor age control is an unexpected lack of peaty sediments at the Kurokoyama site, which is probably related to a high sedimentation rate and an unusual sedimentation process due to rapid soil creep on the mountain slope. Although application of this method might be limited on a mountain slope with rapid soil creep, which is commonly implied by the downslope bending of tree trunks as it is at the Kurokoyama site, our test excavations suggest that pit excavation on a mountain slope basically works as a paleoseismological tool in mountainous regions.

DOI： 10.5026/jgeography.114.5_724

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Language：Japanese   Publisher：Japanese Society for Active Fault Studies  

Pit excavation across a small uphill-facing fault scarp on a mountain slope could be a paleoseismological tool for active faults without suitable sites for traditional trenching. We tested this method on the Neodani fault, which is one of causative faults for the 1891 M 8.0 Nobi earthquake. We found an unnatural small uphill-facing scarp on a mountain slope just along the trace of the fault and decided that the scarp should have tectonic origin. However, pit excavation across it, radiocarbon ages from the pit, and following additional investigation on historical documentations reveal that it is probably one of ruins of a&ldquo; shishigaki&rdquo; (man-made protection wall against damage to crops by wild animals), which was built during the late Edo period (1804-1810 A. D. ). With the knowledge of a shishigaki, we would have previously recognized that the scarp was not a tectonic one: key observations are presence of level land along the scarp that used to be a paddy field (now woods), and common lack of recognizable vertical offset of a mountain slope across the scarp. As ruins of a shishigaki are reported to be widely distributed in all Japan except for Hokkaido and Tohoku regions, great care should be exercised with them in recognizing small fault scarps on a mountain slope.

DOI： 10.11462/afr1985.2004.24_95

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Publishing type：Research paper (scientific journal)  

Sources of catastrophic earthquakes include not only major active faults, but also those with low slip rates. Geologic observations of two Japanese surface-rupturing earthquakes on low slip-rate strike-slip faults (the 1927 Kita-Tango and the 1943 Tottori earthquakes) suggests a concept of "threshold of geomorphic detectability" for strike-slip faults in humid mountainous regions. This threshold must be exceeded in order that progressive coseismic surface offset can be preserved as detectable faulted topography that may be otherwise erased by surface processes. The determined threshold minimum slip rates for both examples are about 0.1 mm/yr, which can be a quantitative explanation for lack of recognition and mapping of many active faults with slip rates of less than 0.1 mm/yr in Japan islands. Although this threshold is probably negligible in arid regions, it can produce another type of unrecognized active fault in humid mountainous regions, in addition to blind thrusts beneath thick sediments.

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Language：Japanese   Publisher：Tokyo Geographical Society  

Trench excavation is a less effective paleoseismic investigation for intramontane active faults because there are fewer good trench sites along them. We propose a new method called &ldquo;pit excavation on a mountain slope&rdquo; to determine the timing of the latest events of such faults. This method is carried out across a small uphill-facing fault scarp preserved on a mountain slope. Sediment trapped by the scarp should provide good information concerning the timing of the latest event.<BR>We applied the method to the northern segment of the Daguchi fault, one of the short rightlateral active faults in the Nosaka Mountains, north of Lake Biwa, southwest Japan. The rupture history of the segment has remained unknown because no good trench site exists along the fault trace. However, our precise geomorphological mapping revealed the presence of a 1 m-high uphill-facing fault scarp preserved on a mountain slope, and therefore we carried out a pit excavation across the scarp using man power. A very clear fault and 75 cm-thick trapped sediments were observed on the pit wall. Since these sediments showed neither displacement nor deformation associated with surface faulting, we interpret that they were all deposited after the latest event. For more accurate age control, we identified species and portion for wood fragments from the sediments. Unfortunately, all samples except those that could not be identified were parts of Cryptomeria japonica, Chamaecyparis obtusa Endl. or Cupressaceae, which can live for hundreds or even thousands of years : this means a possible large offset between deposition and radiocarbon age for these samples, leading to less accurate age control. However, some of them were from the outermost trunk, for which we can regard radiocarbon age as the deposition age in consideration of the very small catchment area of the pit site (several hundreds of m²). Based on the radiocarbon ages of the outermost trunk samples, the initiation of sediment trapping or equivalently the timing of the latest event is estimated to be about 1500 years ago (5th to 7th century AD).<BR>Our investigation on the Daguchi fault successfully revealed the accurate timing of the latest event, supporting the effectiveness of our new method. However, some problems remain unsolved, including application of the method to other faults, especially those with long dormancy, and necessity of a crosschecking excavation on a historically ruptured fault.

DOI： 10.5026/jgeography.111.5_747

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Language：Japanese   Publisher：Japanese Society for Active Fault Studies  

Surface rupture with maximum right-lateral displacement of 150cm and length of about 1 lkm was observed during the 1943 Tottori earthquake of Mw: 7.0, which struck the eastern Tottori prefecture, southwest Japan. We compiled all the previous reports and papers regarding the surface rupture associated with the earthquake as precise location maps (Appendix 1) and a data table (Appendix 2). We also showed the slip distribution along the surface rupture (Fig.3).<BR>The trace of the 1943 surface rupture exhibited the large step and quite sinuous geometry compared with other strike-slip surface breaks. This observation probably means that the causative fault for Tottori earthquake is at the infant stage on its way of evolution based on the Wesnousky's fault evolution model (Wesnousky,1988). Most of the surface rupture during the earthquake occurred along the geomorphologically detectable active fault (Shikano-Yoshioka active fault system). Thus, we can recognize the possible surface faulting event around the epicentral area based on recent understanding of tectonic geomorpholgy. However, the length of the subsurface seismogenic fault is underestimated by the presently proposed method (Odagiri and Shimazaki,2000) and this sh ould lead to crucial underestimation of the seismic moment and also strong ground motions. The method to estimate the lengt h Df the seismogenic fault must be reestablished.

DOI： 10.11462/afr1985.2002.21_73

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Language：Japanese   Publisher：Japanese Society for Active Fault Studies  

Surface-rupturing earthquakes tend to cause larger damage than earthquakes without surface rupture (Takemura,1998). However, the degree of damage during an earthquake is largely influenced by population, surface geology and strength of houses in the epicentral area. I calculated the index valueIby eliminating the effects of population, surface geology and strength of houses from compiled damage data of 37 earthquakes occurred intraplate Japan during the past 115 years:I=D/(j&sdot;k&sdot;D₇) whereDis number of collapsed houses during an earthquake, D₇, is calculated number of collapsed houses when a point source of moment magnitude Mw: 7.0 (depth: Okm) is assumed at the epicenter, j is a coefficient of calibration for population chang e through time, and k is a coefficient of calibration for strength change of houses through time. A damage estimation program by National Land Agency of Japan is used for the damage calculation.<BR>Ivalues for surface-rupturing events are expected to be at leas t a factor of ten larger than those for events without surface rupture in the range of Mw: 6.4-6.6 which is an over-lap zone of both types of events. The difference of depth to the upper edge of the seismogenic fault between both types of events possibly explains this observation. However, I interpret it to suggest that source property changes when rupture cuts free surface and this might cause larger damage.<BR>All of the earthquakes ofI>0.5 are surface-rupturing events except ones which occurred beneath alluvial plains. Since all of surface-rupturing events occurred by movements of geomorphologically detectable active faults, I can empirically conclude that earthquake with large potential to cause great damage always occurs on geomorphologically detectable active fault except one beneath alluvial plain.

DOI： 10.11462/afr1985.2001.20_23

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Language：Japanese   Publisher：Tokyo Geographical Society  

The Mitoke active fault system (MAFS) is about 50 km long with a NW-WNW strike in the western margin of the Tamba Mountains, and is generally characterized by an uplifting of the northeast side accompanied by a left-lateral slip. The MAFS is composed of many active faults and is one of the largest active fault system in the northern Kinki district. The Tonoda fault is situated in the central part of the MAFS and is about 15 km long. Based on a study of the fault topography, the Tonoda fault acted with an uplifting northeastern side and a left-lateral slip during the late Quaternary period. A paleoseismological study was requested due to the lack of evidence on which to base on evaluation of earthquake risk.<BR>To clarify the age of the latest event and intervals of events of the Tonoda fault during the late Quaternary, trenches were excavated across the fault scarplet at Sekibayashi where this fault cut river terraces with a NW trend.<BR>The results of this study can be summarized as follows:<BR>This fault is a reverse fault with northeastern side up-thrown and fault planes dips about 80&deg; to the north. Based on differences of geologic section and fault striation, this is accompanied by a left lateral slip.<BR>1) The vertical displacements of depositional surfaces of Li and L2 terraces are 5 to 9m and 1.9-3m respectively, based on drilling and trenching data. This fault is characterized by a average vertical slip rate of 0.1-0.3m/1, 000 years during the late Quaternary period.<BR>2) At trench B, three faulting events were identified since 11 ka. The latest event was dated to be 1, 950-2, 310y. B. P.(A. D. 100-B.C. 395), that is from the Middle Yayoi to Latest Jomon period. The second and third latest events were dated to be 5, 500-7, 500y. B. P, and 8, 500-10, 710y. B. P. The average reccurence interval of faulting is estimated to be about 3, 740 years. A much older faulting event from 17, 000-22, 000y. B. P. was only identified at trench A because of the poor resolution for a paleoseismicity analysis.

DOI： 10.5026/jgeography.109.73

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Publisher：Tokyo Geographical Society  

DOI： 10.5026/jgeography/109.1_plate7

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Language：Japanese   Publisher：Tokyo Geographical Society  

DOI： 10.5026/jgeography.108.276

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Publisher：Springer Nature Singapore  

DOI： 10.1007/978-981-19-1150-7_3

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Publisher：Springer Nature Singapore  

DOI： 10.1007/978-981-19-1150-7_10

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Language：Japanese  

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Language：Japanese   Publisher：National Institute of Polar Research  

DOI： 10.15094/00013477

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Language：Japanese   Publisher：The Institute of Electrical Engineers of Japan  

In order to mitigate landslide risks, monitoring of ground water is essential. Previous indoor experiments suggest that the self-potential approach has an advantage to establish the early warning system in performance to detect related signals and in cost. To evaluate results obtained from the previous indoor experiments, in-situ measurements are required. To achieve this, we selected a test slope at Nishiikawa, Tokushima, Japan and we performed preliminary electrical resistivity exploration (ERT) and core-sampling. The results of ERT show that there are low resistive areas in shallow depth ( < 3 m). The core-sampling results also indicate that there exists the structure which corresponds to slip surface. In addition, anisotropy in magnetic susceptibility was examined and the samples around the estimated the slip surface region provide the oblate ellipsoid characteristics. These results of ERT and core analyses are consistent and make convince the identification of the slip surface. Based on these preliminary results, we set up the in-situ self-potential observation at the slope and started measurements.

DOI： 10.1541/ieejfms.136.297

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Language：Japanese  

J-GLOBAL

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Language：Japanese  

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Language：Japanese   Publisher：The University of Tokyo  

We present new, high-resolution seismic reflection data (2000 Inabe River profile) acquired across the forelimb and backlimb of Kuwana anticline to further image its subsurface geometry. A seismic source (mini-vibrator) and 150-channel digital telemetry recording system were used in an off-end configuration with the nearest receiver adjacent to the source to record seismic waves from deeper reflection points. A 15-m source and geophone spacing give a 7.5-m CMP (common midpoint) spacing on the final section. The nominal CMP stacking fold had 75 traces. We also suppressed coherent noise by repeating source points 5-10 times. After data processing including surface-consistent statics, velocity analysis, normal moveout (NMO) correction, residual statics, CMP stack, and migration, the section was finally depth-converted using stacking velocities. Reflectors imaged on the seismic profile illuminate that fluvial terraces folded across the forelimb and backlimb are consistent with the subsurface structure of the fold imaged in a seismic section, providing insights into the kinematic solution of the underlying active wedge thrust.

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Other Link： http://hdl.handle.net/2261/8152

Language：Japanese   Publisher：海洋出版  

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Language：Japanese   Publisher：実業公報社  

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Language：Japanese   Publisher：海洋出版  

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Language：Japanese   Publisher：四国総合研究所  

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Language：Japanese   Publisher：歴史地震研究会  

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