Southern Central Japan Research Articles

High-resolution three-dimensional azimuthal velocity anisotropy of S-waves in southern-central Japan, based on ambient noise tomography

To investigate the dominant deformational patterns and stress conditions in the upper crustal structure of the Kinki region, southern-central Japan, we constructed a high-resolution 3D azimuthal anisotropy model to a depth of ~ 11 km. We used 6-month-long ambient noise data recorded by the densely distributed permanent and temporary stations. From this dataset, cross-correlations were retrieved. We then obtained a 3D isotropic velocity model by inverting Rayleigh wave dispersion data, followed by a direct joint inversion for both 3D azimuthal anisotropy and additional isotropic velocity perturbation. The resolved 3D azimuthal anisotropy reveals significant contrasts of anisotropy across the Kinki region. The predominant fast axes observed in the northwestern Kinki region align with the direction of the maximum horizontal compressional stress and the principal strain rate axes, suggesting that the observed anisotropy is mainly stress-induced. In the southern part of the study area, furthermore, the predominant fast axes trend NE–SW and near E–W, also indicating the presence of stress-induced anisotropy. On the depth profile of the anisotropy, we found depth-dependent variation of azimuthal anisotropy. There exists a significant consistency between the anisotropy observed beneath 3 km depth and the dense distribution of earthquake hypocenters. This interrelationship between anisotropy and seismicity demonstrates that the observed anisotropy could be linked to local crustal stress or fractures relevant to earthquake ruptures. Our 3D anisotropy model therefore contributes towards understanding the locations and features of the seismicity region.Graphical

First record of Neoporphyra haitanensis (T.J.Chang & B.F.Zheng) J.Brodie & L.‐E.Yang (Bangiales, Rhodophyta) from Shikinejima Island and Hachijojima Island of the Izu Islands, southern central Japan

SUMMARYWe conducted a morphological observation and molecular phylogenetic analyses on bladed Bangiales collected from natural populations on Shikinejima Island and Hachijojima Island of the Izu Islands, southern central Japan. The morphological features of the gametophytic blades such as the blade shape, blade margin and reproductive cell divisions were extremely similar to those parameters of Neoporphyra haitanensis, a species cultivated in southern China, and Neoporphyra dentata. However, the blades collected from the two islands were thicker than the blades of N. dentata; this feature was the same as that of N. haitanensis. The chloroplast RUBISCO spacer sequences of present samples were identical to the sequences of N. haitanensis from China. Moreover, phylogenetic positions of three conchocelis strains isolated from the blades on the two islands were examined based on concatenated sequences of the chloroplast rbcL gene and nuclear 18S rRNA. The results showed that the strains were resolved in a clade including N. haitanensis; however, the strains were separated from N. haitanensis in China. Therefore, the bladed Bangiales from the two islands were identified as N. haitanensis. The present study is the first record of N. haitanensis in natural populations in Japan.

Comparison of the Circulation Anomalies Associated with Wet and Dry Extreme Heat in South Korea and Southern–Central Japan

AbstractThis study indicates a significant variation of humidity on extreme heat (EH) days over South Korea and southern–central Japan during the period 1979–2018. EH is therefore classified into three categories: type-A wet EH, type-B wet EH, and dry EH. Their statistical characteristics and formation mechanisms are investigated and compared. Our results suggest that the type-A wet EH is the most destructive, with the highest intensity, longest duration, and broadest spatial scale covering most of midlatitude East Asia. By contrast, type-B wet EH and dry EH are weaker, shorter, and mostly confined to northeast Asia. Despite these differences in characteristics, both types of wet EH are caused by the poleward advance of tropical warm and humid air masses as a result of the northward displacement of the Asian westerly jet. By contrast, dry EH is primarily induced by an increase in adiabatic heating and solar radiation resulting from anomalous subsidence. The three types of EH are associated with distinct large-scale teleconnections over Eurasia. A stable and persistent tripole wave pattern is responsible for type-A wet EH. The activity of atmospheric blocking over northern Europe, where the pattern originates, plays a crucial role in maintaining this pattern. By contrast, type-B wet EH and dry EH are related to a quadrupole pattern and a Silk Road pattern–like teleconnection, respectively, both lasting for a shorter time. These results highlight the diversity of EH, which suggests that multiple local and large-scale circulations should be considered to improve the forecast skills for EH.

Large-Scale Circulation Anomalies Associated with Extreme Heat in South Korea and Southern–Central Japan

AbstractThe large-scale circulation anomalies associated with extreme heat (EH) in South Korea and southern–central Japan are examined using data during the time period 1979–2016. Statistical analysis indicates that EH days in these two regions are concentrated in July and August and tend to occur simultaneously. These EH days are therefore combined to explore the physical mechanisms leading to their occurrence. The composite results indicate that the anomalous atmospheric warming during EH days is dominantly caused by a significant subsidence anomaly, which is associated with a deep anomalous anticyclone over East Asia. Further investigation of the evolution of circulation anomalies suggests that the anomalous anticyclone over East Asia related to EH is primarily initiated by wave trains originating from upstream regions, which propagate eastward along the Asian westerly jet in the upper troposphere. These wave trains can be categorized into two types that are characterized by the precursor anticyclonic and cyclonic anomalies, respectively, over central Asia. The distinction between these two types of wave train can be explained by the wavenumbers of the Rossby waves, which are modulated by both the intensity and the shape of the Asian westerly jet as the background basic flow.

「徳島県日和佐川における淡水産エビ類の分布パターン形成要因」の紹介(2013年度日本甲殻類学会・学会賞受賞論文研究紹介)

「徳島県日和佐川における淡水産エビ類の分布パターン形成要因」の紹介(2013年度日本甲殻類学会・学会賞受賞論文研究紹介)

GPS 観測による神津島島内における地殻変動 (1996年7月-1997年11月)

GPS 観測による神津島島内における地殻変動 (1996年7月-1997年11月)

A14 2000 年以降の神津島周辺域における地殻上下変動と圧力源の推定

A14 2000 年以降の神津島周辺域における地殻上下変動と圧力源の推定

The role of flood regime on invasive success of exotic species growing in riparian environments

To elucidate the conditions under which exotic species become invasive, we compared the performance of Veronica anagallis-aquatica (exotic) and V. undulata (native) in Kansai, southern-central Japan, where the former species is highly invasive, with performance in a region where this species is less invasive (Kanto, eastern Japan). We compared the micro-environments, including scale and frequency of flooding, of these species in both Kansai and Kanto. We also conducted growth experiments on seedlings from both regions to compare their responses to varying water conditions. Four treatments were conducted: a dry treatment where neither roots nor shoots were flooded; a flooded treatment where both roots and shoots were flooded; a moist treatment where only roots were flooded; and a variable treatment where the water level was shifted between that in the flooded and dry treatments. We found that the flooding frequency was higher in Kansai than in Kanto, whereas the flow peaks were almost four times higher in Kanto than in Kansai. The mean stem internode length was longer in the variable treatments than in the other treatments in the V. anagallis-aquatica seedlings derived from Kansai, but did not differ among treatments in both V. anagallis-aquatica and V. undulata seedlings derived from Kanto. V. anagallis-aquatica in Kansai evolved a strategy to evade flooding by stem elongation. However, that species did not show elongation traits in Kanto, possibly because it could not respond to large-scale flooding. V. anagallis-aquatica may show adaptive evolution in specific habitats where it can respond adaptively.

Factors affecting distribution of freshwater shrimps and prawns in the Hiwasa River, southern central Japan

Factors affecting distribution of freshwater shrimps and prawns in the Hiwasa River, southern central Japan

Coastal barrier dune construction during sea-level highstands in MIS 3 and 5a on Tottori coast-line, Japan

The southern coast of Japan Sea exhibits a number of Late Pleistocene coastal barrier dunes, where the sediment record potentially provides important evidence for the palaeoenvironmental history of East Asia. The lack of direct dating of these barrier dunes, however, has veiled relationships between dune deposition, sea level, and other controlling factors. Quartz single aliquot regenerative optically-stimulated luminescence (OSL) dating was applied to the Late Pleistocene barrier dune at the Tottori coast, southern central Japan Sea. We investigated a borehole drilled in a continuous ground-penetrating radar (GPR) profile of the dune and an outcrop excavation, where there has been recognised a sedimentary succession exposed of the Pleistocene dune sand, palaeosol, Daisen–Kurayoshi Pumice (DKP) tephra, palaeosol, and Holocene dune sand, in ascending order. The gradual transition from the Pleistocene dune sand to palaeosol indicates a termination of the Late Pleistocene dune activity. Five OSL ages from the uppermost Pleistocene dune overlap within the period 48.2–51.4 ka, which confirms that both deposition and termination of the dune occurred in early to mid Marine Isotope Stage (MIS) 3. Another OSL age from the lower section was 77.7 ± 6.1 ka, and indicates an earlier depositional stage in late MIS 5a. These reveal that the coastal dune deposition occurred in relation to the sea-level highstands. It would appear that a sea level of c. –50 m relative to the present was the threshold for the dune activation. Morphology and sediment distribution of the modern shelf off the Tottori coast suggest that the sea-level lower than − 50 m leads to increasingly unfavourable conditions for coastal dune activity due to longer sediment transport distances and decreased sediment supply. These results have implications for the Late Pleistocene barrier dune along the southern Japan Sea coast and suggest that other dunes, correlated with Tottori based on the DKP tephra, possibly would also have experienced a similar termination in relation to the sea-level fall from mid MIS 3. Results also demonstrate that the depositional setting of the Late Pleistocene dunes was different from those constructed in the Holocene due to the lower interstadial sea-level highstands and resultant longer distance to the shore during MIS 3 and 5a. As a result, the Pleistocene dune exhibits less pronounced stratification and in finer grain size than the outer Holocene dune ridge, where sand is directly fed from the shore. The grain size of the inner Holocene dune ridge in contrast is almost identical to the Pleistocene dune, suggesting that the inner ridge partly consists of sand reworked from the Pleistocene dune.

The Role of Typhoon Songda (2004) in Producing Distantly Located Heavy Rainfall in Japan*

Abstract When Typhoon Songda (2004) was located southeast of Okinawa over the western North Pacific during 2–4 September 2004, a heavy rainfall event occurred over southern central Japan and its adjacent seas, more than 1200 km from the typhoon center. The Advanced Research version of the Weather Research and Forecast (WRF-ARW) model was used to investigate the possible remote effects of Typhoon Songda on this heavy precipitation event in Japan. The National Centers for Environmental Prediction (NCEP) global final (FNL) analysis was used to provide both the initial and lateral boundary conditions for the WRF model. The model was initialized at 1800 UTC 2 September and integrated until 1800 UTC 6 September 2004, during which Songda was a supertyphoon. Two primary numerical experiments were performed. In the control experiment, a bogus vortex was inserted into the FNL analysis to enhance the initial storm intensity such that the model typhoon had an intensity that was similar to that observed at the initial time. In the no-typhoon experiment, the vortex associated with Typhoon Songda in the FNL analysis was removed by a smoothing algorithm such that the typhoon signal did not appear at the initial time. As verified against various observations, the control experiment captured reasonably well the evolution of the storm and the spatial distribution and evolution of the precipitation, whereas the remote precipitation in Japan was largely suppressed in the no-typhoon experiment, indicting the significant far-reaching effects of Typhoon Songda. Songda enhanced the remote precipitation in Japan mainly through northward moisture transport into the preconditioned precipitation region by its outer circulation. The orographic forcing of the central mountains in Japan played a small role compared with Typhoon Songda in this extreme precipitation event.

Transient and permanent deformation of central Japan estimated by GPS

Abstract We analyze continuous global positioning system (GPS) data to estimate the kinematics of the Philippine Sea plate subduction below southern central Japan. Using a back slip dislocation model, we invert the strain rate tensors derived from the GPS velocity field to obtain the velocity of the downgoing slab with respect to the Tokai and Kanto forearcs along the eastern Nankai-Suruga and Sagami troughs, respectively. In both cases, these velocities are smaller and slightly rotated with respect to the Philippine Sea plate subduction velocity in central Nankai. This result implies strain partitioning between the subduction thrusts and on land and/or offshore deformation zones in both the eastern Nankai-Suruga and the Sagami area. In southern Kanto, we predict ∼20 mm yr −1 of dextral shear, in agreement with motion observed along the Boso strike-slip fault. In the Tokai region, the slip deficit accumulated since the last earthquake (1854) ranges between 6 and 3 m. Considering the extent of the locked zone, it would correspond to a magnitude M W =8.15 earthquake, if the slip deficit were to be released now during a single event.

Nonmetric Cranial Variants in a Medieval Japanese Sample from Ichikishima-jinja Site.

The incidences of 20 nonmetric cranial traits of medieval Japanese skeletons excavated at the Ichikishima-jinja site in southern central Japan are reported, and compared with those of other population samples from Japan by means of Smith's Mean Measure of Divergence (MMD). The Ichikishima sample is proved to be biologically far from both the prehistoric Jomon and recent Hokkaido Ainu samples, and close to the samples from the protohistoric Kofun to the recent period, especially to the Kanto samples of the Muromachi and Kamakura periods. For both the recent and Kofun periods, the Ichikishima sample is closer to the eastern then to the western Japan samples. A secular trend, which is perhaps independent of the extent of admixture between the Jomon and immigrant elements, is suggested for the Japanese samples after the Yayoi period.

三浦・房総半島新第三紀三浦層群の石灰質ナノ化石年代および対比

三浦・房総半島新第三紀三浦層群の石灰質ナノ化石年代および対比