Southwest Kyushu Research Articles

Long-Term Trend and Inter-Annual Variation of Ocean Heat Content in the Bohai, Yellow, and East China Seas

The long-term trend and interannual variation of ocean heat content (OHC) in the Bohai Sea, Yellow Sea, and East China Sea (BYECS) were examined using 27 years (1993–2019) of daily reanalysis data from the Japan Coastal Ocean Predictability Experiment 2 (JCOPE2M). The annual mean OHC was 4.25 × 1021 J, with a linear warming rate of 0.13 W m−2 with a confidence level of 95%. The spatial distributions for the annual and linear trends of OHC in the BYECS were inhomogeneous, and a considerable quantity of heat was stored on the outer shelf. The warming rate was considerably elevated in the areas northeast of Taiwan and southwest of Kyushu, showing a rate greater than that of the Pacific and global oceans by a factor of 4–5. Heat budget analysis indicated that the Taiwan Strait (TAS) is the dominant source of heat for the BYECS. The mechanisms of the OHC interannual variation in the outer and inner shelves varied. On the outer shelf, the OHC interannual variation was dependent on the Kuroshio onshore intrusion, while on the inner shelf, the OHC interannual variation was related to the variation in air-sea heat flux. The rapid warming in the outer shelf corresponded to the increasing trends of heat transport across northeast Taiwan and southwest Kyushu, which were dominated by the temporal variation of current velocity.

南部八代海における底生有孔虫の L/Tl 値から見積もられる相対的堆積速度とタフォノミー

南部八代海における底生有孔虫の L/Tl 値から見積もられる相対的堆積速度とタフォノミー

西南部九州2型アクセントの特性の比較 : 助詞・助動詞のアクセントを中心として( N型アクセント研究の現在)

西南部九州2型アクセントの特性の比較 : 助詞・助動詞のアクセントを中心として( N型アクセント研究の現在)

九州南部北薩地方西目地域の仏像構造線相当の地体構造境界

The Nishime area of Hokusatsu District, southwest Kyushu, Japan, is underlain by a chert-clastic complex comprising the Nitao and Momigi Units of Chichibu Belt; a mélange of sandstone, chert, and limestone clasts in an argillaceous matrix, corresponding to the Omae Unit of Chichibu Belt; and coherent sandstone-mudstone formations that belong to the Saiki Subgroup of the Shimanto Belt. These pre-Paleogene bedrock formations are mostly covered by Neogene and younger formations. On the basis of detailed geologic mapping of this area, we propose two precise locations for the boundary between the Omae Unit and the Saiki Subgroup. This boundary is traditionally called the Butsuzo Tectonic Line (BTL). The first proposed location is on the Ushinohama coast, where a brittle shear zone separates the Saiki Subgroup from the mélange of the Omae Unit. Here, deformation structures in the shear zone indicate northeastward thrust of the hanging wall of the Omae Unit. The second location is at Chugenda. Although direct contact is not exposed at the Chugenda location, a mélange similar to the hanging wall of the Ushinohama coast shear zone is juxtaposed against coherent beds of sandstone and mudstone. We suggest that a geotectonic boundary corresponding to the BTL runs through the Ushinohama coast and Chugenda.

South-Vergent Imbricate Fan in the Ikenodan Formation of the Shimanto Supergroup, Southern Kyushu, Japan

The Noda area in Hokusatsu District, southwest Kyushu is underlain by Imanokoba, Ikenodan and Ogakura Formations of Cretaceous Shimanto Supergroup. The Imanokoba Formation comprises beds of sandstone and mudstone. The beds generally trend NE-SW and dip in a moderate to steep angles to east or west. The Ikenodan Formation comprises beds of sandstone, mudstone, siliceous mudstone and chert and basaltic lavas. The beds generally strike between NE and NW, and dip toward west in moderate to high angles with a westerly way-up. The chert and basaltic lava beds appear in a left-stepping en echelon arrangement. The contact between Imanokoba and Ikenodan Formations is in a N-S trending fault known as Noda Fault. The Ogakura Formation is composed of alternating beds of sandstone and mudstone. The beds generally strike between NE and NNE and dip toward west in moderate to high angles with westerly way-up. The contact relationship between Ikenodan and Ogakura Formations is not distinct. The westward disappearance of basaltic lava marks western limit of Ikenodan Formation. The en echelon array in Ikenodan Formation is interpreted as an imbricate fan with Noda Fault on its bottom as a decollement and is called the Ikenodan imbricate fan. The Ikenodan imbricate fan is considered to have been formed in an accretionary complex developed in a northbound subduction zone. The primary attitude of Ikenodan imbricate fan was probably south-vergent then turned over with its west side down. It was previously reported that strata of Shimanto Supergroup in Hokusatsu area form a regional bending structure called the Hokustasu Bend. The Noda area is situated in a hinge zone of Hokusatsu Bend, although formations in Noda area have not been involved in bending structure. The Ikenodan Formation and Noda Fault presumably extend to north without bending, otherwise bending structure occurs anywhere outside Noda area. In either case, Hokusatsu Bend is not present as interpreted in previous studies.

Atmospheric pressure-wave bands around a cold front resulted in a meteotsunami in the East China Sea in February 2009

Abstract. A meteotsunami hit southwest Kyushu on 25 February 2009, with an estimated maximum amplitude of 290 cm, which was higher than that recorded for the 1979 Nagasaki event. This study investigated mesoscale meteorological systems over the East China Sea during the time leading up to the February 2009 event using a Weather Research and Forecast model. The disturbance in the sea-level pressure originated from a gravity wave over southeastern China. The sea-level pressure disturbance observed and modelled over the East China Sea had its source over the southeastern China mountains and was then propagated by a jet stream toward western Japan with the help of both wave-duct and wave-CISK (conditional instability of the second kind) mechanisms. Two synoptic systems supported the momentum convergence and the formation of band-shaped unstable layers in the mid-troposphere. The high-latitude trough extended from eastern Siberia and there was subtropical high pressure over the western Pacific Ocean. The phase speed of the atmospheric wave was as high as 25–30 m s−1, corresponding to the phase speed of long ocean waves on the East China Sea. Improvements in determining the amplitude and timing of the disturbance remain for future work.

Food habits of fishes on an exposed sandy beach at Fukiagehama, South-West Kyushu Island, Japan

To clarify the feeding habits and major food sources of sandy beach fishes, the gut contents of 55 fish species collected on a sandy beach at Fukiagehama, South-West Kyushu Island, Japan, were examined. Ontogenetic changes in food preference were recognized in nine species (Hypoatherina valenciennei, Lateolabrax japonicus, Trachurus japonicus, Sillago japonica, Sphyraena japonica, Paralichthys olivaceus, Heteromycteris japonica, Paraplagusia japonica, and Takifugu niphobles). A cluster analysis based on dietary overlaps showed that the sandy beach fish assemblage comprised six trophic groups (mysid, amphipod, zooplankton, juvenile fish, terrestrial insect, and mollusk feeders). Of these, the first three groups were the most abundantly represented, whereas the last two were represented by only a single species. These results indicated that epibenthic macrofauna, such as mysids and gammaridean amphipods, and zooplankton, were important food resources for the fish assemblage at the study site, but infaunal macrobenthos, such as polychaetes and bivalves, being relatively unimportant.

Methodical Recruiting Systems for High School Jobseekers in Japan

Most migration studies have been done under the premise that individuals migrate of their own freewill. In recent years, however, some researchers insist that various “systems” promote or restrain the migration of jobseekers.In this paper, we researched some cases in migration for the employment of female high school graduates where methodical recruiting systems have played a very important role and have caused massive migration as a result.We examined two kinds of occupations, spinning mill workers and assistant nurses, in the Chukyo metropolitan area that includes Nagoya and Gifu. We found that female workers in these occupations quit after a relatively short term and that the employers wanted to continue to keep finding new workers in both occupations. They provide incentive systems where female workers can work and study at junior colleges and other educational institutions. In Southwest Kyushu, a peripheral region in Japan, we also found that there were not enough local jobs for female high school graduates seeking jobs and that the ratio of students going on to higher education was also low because their incomes were not as high there.We discovered that because of the satisfaction of both interests, those in the Chukyo metropolitan area and those in Southwest Kyushu, many female high school graduates seeking work in Southwest Kyushu were employed in these two kinds of occupations in the Chukyo metropolitan area since the 1980s. Furthermore, the recruiting systems of these occupations in the Chukyo metropolitan area are highly methodical. The people in charge of employment for both occupations who conduct recruiting activities in Southwest Kyushu have also maintained strong personal relations with the guidance-counseling teachers at high schools in Southwest Kyushu. Therefore the number of migrants from Southwest Kyushu to the Chukyo metropolitan area for both occupations is maintained at a relatively high level, in contrast with the general trend of the number of migrants from all peripheral regions to the three largest metropolitan areas (Tokyo, Chukyo, and Hanshin metropolitan area), for the employment of female high school graduates.We found that the ratio of migrants to the Chukyo metropolitan area was the highest among all migrants for the employment of female high school graduates from Southwest Kyushu in the three largest metropolitan areas, although the ratio of migrants to the Tokyo metropolitan area was generally the highest among all the migrants from Southwest Kyushu and the other peripheral regions to the three largest metropolitan areas in Japan. This phenomenon is one example in which the “systems” affected macroscopic migration patterns.

鉱物資源探査における空中物理探査の現状と将来

Airborne geophysical survey methods, such as magnetics, electromagntics, and radiometrics, are well known, have numerous applications, and are regularly employed in regional surveys around the world by both governments and private organizations. Technology regarding each of these methods has gradually improved and along with it, the introduction and necessary accuracy in Global Positioning Systems (GPS), the introduction of image processing techniques allowing a greater range in data display compared with conventional contouring, and the availability of multi-client data sets resulting in significant cost reduction. Airborne geophysical methods have long been recognized as a valuable geological survey tool since the first airborne magnetic survey was flown in 1936 as part of a mineral exploration program. The Metal Mining Agency of Japan (MMAJ) has for more than three decades employed airborne geophysical methods in both its domestic and overseas mineral exploration programs. In general, the surveys provide a wide range of data concerning lithological variation, structure, and features peculiar to mineralization. Domestically, the MMAJ has employed airborne magnetic surveys since 1969 as part of their regional exploration program, and airborne electomagnetic and magnetic surveys since 1975, initially as part of their research into the application of these methods in the search for Kuroko and epithermal style mineralization. A direct result of this work was the discovery of the Hishikari deposit, Japan's premier gold mine. In 1996, the MMAJ embarked on a new program of high-resolution airborne magnetic and radiometric surveys, beginning in the Hokusatsu region of southwest Kyushu. The results confirmed the importance and application of these sensors in the search for low sulphidation epithermal style gold mineralization. High-resolution geophysical surveys remain an integral part of the domestic survey departments current activities. Overseas, the MMAJ began its history of airborne surveys in Zaire in 1968 with a fixed-wing magnetic survey. Since that time a range of sensors have been employed around the world for various styles of mineralization, the most recent being a helicopter survey this year in the Bicol region of the Philippines targeting porphyry and epithermal copper-gold deposits. Although the above mentioned methods have been successfully employed in the search for mineral deposits, they are equally important in other fields. The identification and surveying of faults, slope stability, dam site identification, transport and land-use planning, electric power line construction, underground surveying, and the monitoring of radioactive elements, are just a few of the applications currently employed by both government and private organizations. Airborne geophysical surveys provide an important and essential data source which should be undertaken as part of Japan National Mapping Program with both current and future multipurpose users in mind. Additionally, it is critical that the government continue to develop the necessary technology concerning data acquisition, processing, analysis, and interpretation, and build upon the high standards, already established within the MMAJ. Such a program is believed to be a matter of national importance.

Distribution of Todarodes pacificus (Cephalopoda: Ommastrephidae) paralarvae near the Kuroshio off southern Kyushu, Japan

The distribution and abundance of Japanese common squid [Todarodes pacificus (Steenstrup, 1880)] paralarvae off southern Kyushu Island near the Kuroshio were examined in relation to water types in the region. Surveys were conducted in 1996 and 1997 using paired, 70 cm diameter Bongo nets. Temperature–salinity plots from 0, 50 and 100 m depths were used to assign sampling stations to three water types: inshore, mixing and Kuroshio. In total, 4103 T. pacificus paralarvae were collected at 59 of 72 stations. Catch densities at positive stations ranged between 8 and 4282 ind./50 m2 sea surface area. Catches during both years were highest in mixing waters, followed by inshore and Kuroshio waters. Total catches were highest just north of the oceanographic front at the inshore edge of the Kuroshio and declined with increasing distance away from the front. Catches of paralarvae ≤1.0 mm mantle length also peaked near the front. In both years, ≥85% of all paralarvae and ≥69% of those ≤1.0 mm mantle length occurred less than 25 km from the front. We conclude that most spawning off southwest Kyushu occurs near the frontal zone, where Kuroshio and inshore waters meet.

Mode of vertical crustal movements during the Late Quaternary in Kyushu, Japan, deduced from heights of ancient shorelines

Data from the ancient shorelines along the present-day coastline of Kyushu Island, western Japan show that the island can be divided into several regions on the basis of modes of vertical crustal movements over the past 125,000 years. The heights of the ancient shorelines have been determined using paleodepth indicators such as molluscan faunas, trace fossils and sedimentary structures. The chronology of the sediments and of the tectonic events has been deduced from the well-documented history of volcanic ash events (tephrostratigraphy) of southern Japan. The difference between the most uplifted and subsided areas the island during the past 125,000 years is about 190 m. Although it was previously thought that the whole of Kyushu Island was a region undergoing uplift throughout this time, the present work shows that there were marked differential movements. North and southwest Kyushu were steadily subsiding areas, but rapid uplift occurred locally in the southern part of the island. A subsiding axis (the Saeki–Sendai Subsiding Axis) crosses the island with a NE–SW trend, and an E–W-trending structural depression (the Beppu–Shimabara Graben) is present in central Kyushu. There is a clear correlation between the present-day coastal landform of the island and the differential tectonic movements that have occurred during the past 125,000 years.

表層堆積物の組成と堆積速度からみた南八代海の堆積環境

表層堆積物の組成と堆積速度からみた南八代海の堆積環境

九州南西部矢筈岳火山岩類のＫ−Ａｒ年代

We determined K-Ar ages for four andesites of the Hisatsu volcanic rocks from Minamata and for rhyolite of the Gesujima welded tuff from Amakusa Shimoshima, southwest Kyushu Japan. The andesites include three Yahazudake volcanic rocks and one Ontake volcanic rocks. The obtained K-Ar ages for the Yahazudake type andesite range from 1.98 to 2.08 Ma. The ages of Ontake type andesite and Gesujima welded tuff are 2.15 Ma and 2.89 Ma respectively. From our new K-Ar age data combined with previously reported geological, petrological and chronological data of the Hisatsu volcanic rocks, we discussed the space and time distribution of these volcanic rocks. Andesites from Hisatsu volcanic rocks are divided into two categories, “Ontake type andesite (K2O>1.7 wt. %)” and “Yahazudake type andesite (K2O<1.2 wt. %)”, based on potassium content in andesite at given SiO2 range (57-63 wt.%). In terms of this criterion, most of the Hisatsu volcanic rocks and andesites from Kirishima volcano are defined as the “Ontake type andesite”. Consequently, the Ontake type andesite distributes whole area of the Hisatsu volcanic province extending from Nagashima area to Kirishima volcano. Andesites of this type, as a whole, have a positive correlation between latest eruption age of each volcano and the distance from the present volcanic front. This spatial arrangement of the Ontake type andesite implies that the width of volcanic zone has narrowed from Nagashima to Kirishima volcano during last three million years. Although the distribution area of Yahazudake type andesites overlaps the Ontake type andesites, the volcanism of the Yahazudake type andesites is quite limited in age ranging from 1.6 to 2.0 Ma. The production of each magma types may belong to different tectonic events.

九州南西海域産ヒラメの成熟年齢と年間総産卵数

Age at maturity and annual fecundity of Japanese flounder were studied with ovaries of 126 females (290-852mm TL) collected in the sea of south-west Kyushu from November to June. Most of the ovaries of females aged 1+ were younger than the yolk vesicle stage. Ovaries of the mature stage were obtained from December to April on females aged 2+, and Janualy to April on those aged 3+ and more, and most of the other ovaries were developed beyond the second yolk stage. The high rate of females with hydrated eggs was obtained in January and February (more than 50%) for females aged 2+ and in February (42%) for those aged 3+ and more, the total frequency of spawning being 4.7 for females aged 1+, 47 for aged 2+, and 23.7 for aged 3+ and more. The relationship between the batch fecundity, N and total length, TL was expressed by N=1.13×103×e(7.24TL×10-3). The annual fecundity in million was estimated to be about 0.1 for a 1+ age female 3.4, for 2+, and 6.87 for a female older than 3+.

九州南西海域産ヒラメＰａｒａｌｉｃｈｔｈｙｓ ｏｌｉｖａｃｅｕｓの年齢と成長

Age and growth of Japanese flounder Paralichthys olivaceus were studied with 198 females and 107 males, totaling 305 specimens (265-875mm in total length) collected in the sea of south-west Kyushu. Judging from changes of the marginal growth index, age marks were formed during the period from January to April in the spawning season. Though significant data was not obtained in males due to shortage of specimens, the growth of females was expressed with the Bertalanffy curve of Lt=840.45[1-exp {-0.406(t+0.067)}] (Lt, total length; t, age). The growths of Japanese flounders around Japan were compared among 19 localities, and divided into three groups: the slow growth in the Touhoku and Hokuriku Districts and the Seto Inland Sea, the intermediate growth in the Sanin District, and the fast growth in the Pacific coast south of the Kantou District and around the Kyushu District.

環日本海地域比較層序論（中編）

This article comprises fifteen chapters on Foreword (1), From orography to comparative stratigraphy (2), Older rocks in the southwestern part of the Soviet Priomrie and its adjacence (3) and Older rocks in the east Manchurian mountainous land, South Manchuria and the Korean peninsula (4) in Part I, the Triassic and Jurassic systems in Southwestern Primorie (5), the Akiyoshi mountains and Tsushima basin (6), the Cretaceous system of the Sikhote Alin and the Sakawa orogeny (7) and the Amur subgeosyncline and the Sungari basin (8) in part II and the Cenozoic systems on the northwestern side of the Japan sea (9), from the destruction of the Tsushima basin to the construction of the shore line of the Japan sea (10), the Akiyoshi and Sakawa folded mountains (11), the PeriTunghai geotectonic zone (12), the Fossa Magna and Uetsu subgeosyncline (13), sundry notes concerning the Geology of the Japan sea (14) and the summary and retrospect (15) in this part, HI to which a comprehensive bibliography (16) is appended.It is well known that the Chichibu geosyncline which was confluent with the Mongolian one at the Touman-Suifung and adjacent areas, turned out the orogenic zone from the continental side by the early Mesozoic and later orogenies. As detailed here, the Triassic Akiyoshi folded mountains were located on the same line with the contemporaneous Songnim mountains in North Korea and not very far removed from the Touman area and the Sikhote Alins. The Akiyoshi mountains were later deformed and the late Jurassic inland sea to the north of the Eo-Nippon cordillera became land by the Oga orogeny causing a long shifting of the folded mountains to the south as shown in fig. 7. It is still a question how far W est Japan was displaced to the south by the Sakawa orogenies in the Middle Cretaceous-Palaeocene age. It is, however, certain that Northeast Japan has advanced much more than Southwest Japan toward the oceanic side by these orogenies in addition to the Tertiary disturbances. Likewise, the Ryukyu islands advanced further toward the Pacific basin than West Japan forming a distinct flexure at Southwest Kyushu.

Microphenocrystic pyrrhotite from dacite rocks of Satsuma-Iwojima, southwest Kyushu, Japan and the solubility of sulfur in dacite magma

Microphenocrystic pyrrhotites were observed in the glassy groundmass of two dacite rocks from Satsuma-Iwojima, southwest Kyushu, Japan. It suggests that the dacite magma was saturated with respect to pyrrhotite at the time of eruption, and thus the sulfur contents in the groundmass can be taken as the solubility of sulfur in the dacite magma. The solubility of sulfur in the dacite rocks thus calculated is 65 to 72 ppm sulfur at the estimated conditions of T=900±50°C, $$f_{{\text{O}}_{\text{2}} } = 10^{ - 12 \pm 1}$$ and $$f_{{\text{S}}_{\text{2}} } = 10^{ - 0.6 \pm 0.6}$$ atm.

Analysis of multiple birth rates in Japan. III. Secular trend, maternal age effect and geographical variation in triplet rates.

Over-all triplet birth rate in Japan was decreased during 1955 to 1967 and 1974. Monozygotic rate was slightly decreased with the year, but dizygotic rate as estimated from monozygotic and dizygotic twinning rates was decreased with the year. Trizygotic rate was increased with the year and particularly high in 1974. Monozygotic rate was slightly increased up to the maternal age group of 35–39 years and decreased thereafter. Similar but more marked pattern is seen for dizygotic rate, whereas trizygotic rate seems to be independent of maternal age. Analysis of secular change during the period from 1960 to 1967 indicated a clear decrease of monozygotic rate in the older maternal age groups. The maternal age effect on the increase of trizygotic rate is less clear. The highest monozygotic rate was seen in the northeast Hokkaido District (56 per million). On the other hand, dizygotic rate was slightly higher in the northeast than in the southwest. As to trizygotic rate, the highest rate was seen in the southwest Kyushu District (10 per million). Heterogeneity of geographical variation was indicated in monozygotic and trizygotic rates, but not in dizygotic rate. Underrepresentation of unlike-sexed triplet sets was suggested in two districts. After excluding the two districts, corrected monozygotic rate is 30, and dizygotic and trizygotic rates are 18 and 7 per million, respectively.

鹿児島県下こしき島の黒鉛鉱床とその地質学的意義

The Koshiki Islands are located at southwest Kyushu, and are underlain by the sedimentary rocks belonging to the Himenoura Group (Upper Cretaceous) and Paleogene Tertiary, and granitic rocks intruded into them in Miocene age. The Himenoura Group, forming a northeast-plunging synclinorium, is more than 3, 600meters thick, and is stratigraphically divided into six units, provisionally named A to F by K. Tanaka and Y. Teraoka (1973). Division B is more than 1, 200meters thick and graphite deposits are found in the phyllitic slates at the lowest part of it, subdivision B1 in the Shimokoshiki-Jima. The graphite deposits, the new occurrences in the Upper Cretaceous sediments of Japan, occur in the area about 2km west of Katanoura. There are a few ore bodies in this area, croping intermittently out about 300meters length. Three main ore bodies among them are named the Suzugaura 1 and 2, and Suzugasaki, and these ore bodies are lenticular shape with several meters length and 1 meter thick. The graphite ore consists mainly of fine-grained crystalline graphite and quartz, and subsequently of sericite, chlorite, and plagioclase. The average values for carbon in the ores of these ore bodies range from 30 to 56 percent C. The process of the formation of the graphite deposits in this area is considered as follow: 1) Upper Cretaceous: Sedimentation of the Himenoura Group {Sandstone and slate dominant with carbonaceous deltaic sediments in basal part (B1). 2) Late Cretaceous to Paleogene Tertiary: Himenoura Movement {Slight concentration of carbonaceous materials and them slight graphitization. 3) Miocene: Participation in aplites related with granodiorite intrusion {Migration, concentration and crystallization on of carbonaceous materials. Formation of graphite deposits.

Cretaceous-Tertiary Unconformity in Nagashima, Southwest Kyushu

Cretaceous-Tertiary Unconformity in Nagashima, Southwest Kyushu