Okushiri Island Research Articles

Factor analysis for landslides in Okushiri Island induced by the 1993 Hokkaido Nansei-Oki Earthquake

Factor analysis for landslides in Okushiri Island induced by the 1993 Hokkaido Nansei-Oki Earthquake

Possible northern persistence of Siebold's beech, Fagus crenata, at its northernmost distribution limit on an island in Japan Sea: Okushiri Island, Hokkaido.

Siebold's beech, Fagus crenata, is widely distributed across the Japanese Archipelago and islands in Japan Sea. Similar to the northern limit of the geographical distribution of F. crenata on the mainland of Hokkaido, the northern limit of the distribution of F. crenata on islands in the Japan Sea is observed on Okushiri Island (ca 42°N). To understand the genetic relationships of F. crenata on Okushiri Island, we examined chloroplast (cp) DNA haplotypes and 11 nuclear microsatellite (SSR) loci among 1,838 individuals from 44 populations from Okushiri Island, mainland Hokkaido, and the northern part of the Tohoku region on Honshu Island. We identified 2 cpDNA haplotypes, which represent not only populations on the Japan Sea coast but also those on the Pacific coast and this suggested the Okushiri Island populations might not be formed by single colonization. Genetic diversity of the Okushiri Island populations of nuclear SSR was not lower than the mainland and the STRUCTURE analysis revealed the Okushiri Island individuals were admixed between Hokkaido and Tohoku clusters. Approximate Bayesian computation inferred that divergence between Tohoku and Hokkaido, and admixture between two populations which generated Okushiri populations occurred before the last glacial maximum (LGM), that is, 7,890 (95% hyper probability density (HPD): 3,420 - 9,910) and 3,870 (95% HPD: 431- 8,540) generations ago, respectively. These inferences were well supported by a geological history which suggested an isolation of Okushiri Island from Hokkaido started prior to the Middle Pleistocene. We discuss the possible persistence of F. crenata during the last glacial maximum on northern islands in the Japan Sea such as Okushiri Island.

A comprehensive overview of studies related to the ecology and genetics of Fagus crenata Blume (Siebold's beech, Japanese beech) at the species' northernmost range limit

AbstractTemperate forest species, including Fagus crenata Blume, have been experiencing distributional shifts during the climate oscillation throughout the Holocene epoch. This review describes the distinctive context of F. crenata populations at the northern range from the perspective of past distribution shifts, future expansion predictions, biotic and abiotic interactions in population establishment, forest vegetation characteristics, and genetic diversity during the expansion process. The current northern distribution limit of F. crenata is in southern Hokkaido and Okushiri Islands. Since 1900, a dozen of northern limit hypotheses has advocated the presence of restriction factors; however, the species shows signs of expanding its habitat northward at present. The current northern limit is not determined by physiological limitations because of the fact that artificial plantations of F. crenata grow well beyond its range. Several studies regarding climate scenarios have predicted species persistence in the future. Sociological studies revealed that a decline in vegetation units is observed from the southern to the northern populations on the Oshima Peninsula, Hokkaido. Also, vegetation on Okushiri Island includes remnants of warm temperate flora indicating a physiographic constraint of the F. crenata forest on the island, reflecting a past distributional shift. Most of the current northern marginal populations were revealed to be established at the time of large forest disturbance. The genetic diversity of local populations has been lost during the northward distribution shift due to the founder effect in the colonizing process. Then, the gene flow from rearward populations has dwindled by the completion of the population establishment.

Early autumn diet of introduced raccoon dogs on Okushiri Island, Hokkaido, Japan.

Early autumn diet of introduced raccoon dogs on Okushiri Island, Hokkaido, Japan.

The comparative study on the species composition of Fagus crenata Blume forests in Okushiri Island of southwestern Hokkaido and its surrounding area

The comparative study on the species composition of <i>Fagus crenata</i> Blume forests in Okushiri Island of southwestern Hokkaido and its surrounding area

РЕКОНСТРУКЦИЯ ЭКСТРЕМАЛЬНЫХ ГИДРОЛОГИЧЕСКИХ СОБЫТИЙ ПОЗДНЕГО ГОЛОЦЕНА НА ПОБЕРЕЖЬЕ БУХТЫ ВАЛЕНТИН, ЯПОНСКОЕ МОРЕ

The scale and age of extreme hydrological events that have been manifested over the past 2000 years on the coast of Valentin Bay is established based on stratigraphic study and radiocarbon dating of different facies deposits. The deposits of four major historical tsunamis (1993, 1983, 1644, and the 12th century) and a paleo-tsunami, which occurred between 1700–1800 cal yr BP . BP, were found. Sedimentation zones were mapped. The composition of diatoms in tsunami sands has been studied in detail. Along with marine and brackish water species tsunami waves also carried most freshwater forms that were redeposited from the coastal lake. Much of the material was supplied from depths up to 5 m. The correlation of events with data for the Japanese Islands is carried out. It has been suggested that the most dangerous tsunamis for this part of the Eastern Primorye coast are caused by submarine earthquakes with epicenters located near the Okushiri Island. The tsunamis associated with earthquakes with epicenters located near the northwestern Honshu Island, were less pronounced. Data on the irregular frequency of extreme floods during the last millennium has been obtained. It was established that the pluvial phase of the Warm Medieval Period ended in the early to mid-12th century. During the Little Ice Age, the water content of the rivers was insignificant, only two events, comparable to the catastrophic floods of the late 20th to early 21st century, are known to correspond to the warm phase of the mid-14th century to early 15th century. Only two of the modern floods have left traces recorded in the sedimentary sequences of the Valentin Bay coast.

Molluscs drifted on the coast of Okushiri Island， Hokkaido， Japan

Molluscs drifted on the coast of Okushiri Island， Hokkaido， Japan

Possible Mechanism for the Tsunami-Related Fires That Occurred at Aonae Harbor on Okushiri Island in the 1993 Hokkaido Nansei-Oki Earthquake

In this paper, we investigate the mysterious tsunami fires that occurred at Aonae Harbor on Okushiri Island during the 1993 Hokkaido Nansei-Oki earthquake. Specifically, five fishing boats moored separately from each other in the harbor suddenly caught fire and burned nearly simultaneously with the arrival of the first tsunami wave. However, the ignition mechanism of those fires has, until now, remained largely unknown. At the time the earthquake occurred, an NHK (Japan Broadcasting Corporation, Tokyo, Japan) crew that was on the island to report on its scenic natural attractions just happened to capture video footage of those tsunami-related fires. Using that NHK video footage in combination with eyewitness accounts, this study investigates the spatio-temporal process leading to those tsunami-related fires. For example, one witness said, "There was whitish bubbling in the offshore area and I saw five burning fishing boats moored on the seawall being blown about by the strong winds. The burning boats were swept ashore with the tsunami and ignited the gasoline of a car that was rolling in the waves. The fire eventually spread to the center of the Aonae District." The NHK video footage confirmed flames arising from the five fishing boats almost simultaneously and the shimmering white color of the tsunami waters striking the seawall, which were consistent with the eyewitness testimony. Based on these spatio-temporal data, we propose the following hypothetical model for the origin of tsunami fires. Combustible methane gas released from the seabed by the earthquake rose toward the surface, where it became diffused into the seawater and took the form of whitish bubbles. The tsunami strike on the Aonae Harbor seawall resulted in the generation of large electrical potential differences within the seawater mist, which quickly developed sufficient electrical energy to ignite the methane electrostatically. The burning methane bubbles accumulated on the boat decks, which then burned violently.

Fault model of the 12th century southwestern Hokkaido earthquake estimated from tsunami deposit distributions

Tsunami deposits were collected along the coast of southwestern Hokkaido and Okushiri Island, northern Japan. The distribution of these deposits suggested that large earthquakes and tsunamis have repeatedly occurred off southwestern Hokkaido. Along the southern coast of Okushiri Island, five tsunami sand/gravel layers have been deposited during the last 3000 years. The latest was deposited by the 1741 Oshima–Oshima landslide tsunami and the second by the 12th century tsunami. The later tsunami was probably generated by a large earthquake because submarine seismo-turbidites with similar age exist in the region and a large inland landslide had occurred in Okushiri Island in approximately the 12th century. The ages of paleo-tsunami events prior to the 12th century are 1.5–1.6, 2.4–2.6, 2.8–3.1 ka. In this study, a fault model of the 12th century earthquake was estimated by comparing tsunami deposit distributions and calculated tsunami inundation areas at five sites in Okushiri Island and Hiyama region. Fault model F17, a submarine active fault in the Japan Sea near Oshima–Oshima, is a probable source for this tsunami. Numerical simulation of the tsunami was performed based on fault model F17; we modified the fault parameters (length and slip amount) from the original model to explain tsunami deposit distributions. A shorter length of 104 km and a larger slip amount of 18 m were appropriate for the fault model on the basis of parametric studies. The seismic moment of the earthquake was calculated to be 9.95 × 1020 Nm (Mw 7.9) assuming a rigidity of 3.43 × 1010 N/m2. The estimated fault model is located between the focal regions of the 1993 Hokkaido Nansei-oki earthquake and the 1983 Japan Sea earthquake.

Geology of oddly-shaped rocks on the coast of Okushiri Island, southwestern Hokkaido, and their folklore

Geology of oddly-shaped rocks on the coast of Okushiri Island, southwestern Hokkaido, and their folklore

A petrified wood washed ashore on Tamaura Beach, Okushiri Island, Hokkaido

A petrified wood washed ashore on Tamaura Beach, Okushiri Island, Hokkaido

Clavate Gastrochaenolites produced by the rock boring clam Penitella kamakurensis from Aonae Beach on Okushiri Island, Hokkaido

Clavate Gastrochaenolites produced by the rock boring clam Penitella kamakurensis from Aonae Beach on Okushiri Island, Hokkaido

奥尻地震と夕張炭坑事故に遭遇した妊婦の分娩に対する考察 : 家族や社会の結び付き(災害・大地震後遺症における自己管理の方法)

奥尻地震と夕張炭坑事故に遭遇した妊婦の分娩に対する考察 : 家族や社会の結び付き(災害・大地震後遺症における自己管理の方法)

Stratigraphic records of tsunamis along the Japan Sea, southwest Hokkaido, northern Japan

AbstractThe stratigraphy of tsunami deposits along the Japan Sea, southwest Hokkaido, northern Japan, reveals tsunami recurrences in this particular area. Sandy tsunami deposits are preserved in small valley plains, whereas gravelly deposits of possible tsunami origin are identified in surficial soils covering a Holocene marine terrace and a slope talus. At least five horizons of tsunami events can be defined in the Okushiri Island, the youngest of which immediately overlies the Ko‐d tephra layer (1640 AD) and was likely formed by the historical Oshima‐Ohshima tsunami in 1741 AD. The four older tsunami deposits, dated using accelerator mass spectrometry 14C, were formed at around the 12th century, 1.5–1.6, 2.4–2.6, and 2.8–3.1 ka, respectively. Tsunami sand beds of the 1741 AD and circa 12th century events are recognized in the Hiyama District of Hokkaido Island, but the older tsunami deposits are missing. The deposits of these two tsunamis are found together at the same sites and distributed in regions where wave heights of the 1993 tsunami (Hokkaido Nansei‐oki earthquake, Mw = 7.7) were less than 3 m. Thus, the 12th century tsunami waves were possibly generated near the south of Okushiri Island, whereas the 1993 tsunami was generated towards the north of the island. The estimated recurrence intervals of paleotsunamis, 200–1100 years with an average of 500 years, likely represents the recurrence interval of large earthquakes which would have occurred along several active faults offshore of southwest Hokkaido.

Tsunami deposits recognized in Okushiri Island, southwestern Hokkaido, Japan

北海道南西部奥尻島南端の低地における掘削調査から，泥炭層中に5枚のイベント堆積物を見出した．イベント堆積物の特徴は次の通りである; （1）陸方向および川から離れる方向へ薄層化・細粒化する，（2）級化層理を示す，（3）粒度組成の特徴は河床砂とは異なり，海浜砂に類似する，（4）粒子ファブリックおよび堆積構造から推定される古流向は概ね陸方向を示す，（5）渦鞭毛藻シストおよび底生有孔虫の有機質内膜が産出する，（6）海側前面に標高の高い沿岸砂丘が発達する閉塞した地形において，現海岸線から内陸へ最大450mほど離れた場所まで分布する．以上の地質・地形学的特徴に加え，過去に高潮が調査地域に浸水した記録は認められないことから，イベント堆積物は津波起源である可能性が極めて高い．14C年代測定結果と合わせて考えると，過去3000-4000年の間に1741年および1993年を含めて少なくとも6回の津波が発生しているものと考えられる．

AN ATTEMPT TO DEVELOP AN ENVIRONMENTAL INFORMATION SYSTEM OF ECOLOGICAL INFRASTRUCTURE FOR EVALUATING FUNCTIONS OF ECOSYSTEM-BASED SOLUTIONS FOR DISASTER RISK REDUCTION (ECO-DRR)

Abstract. “Ecological Infrastructure (EI)” are defined as naturally functioning ecosystems that deliver valuable services to people, such as healthy mountain catchments, rivers, wetlands, coastal dunes, and nodes and corridors of natural habitat, which together form a network of interconnected structural elements in the landscape. On the other hand, natural disaster occur at the locations where habitat was reduced due to the changes of land use, in which the land was converted to the settlements and agricultural cropland. Hence, habitat loss and natural disaster are linked closely. Ecological infrastructure is the nature-based equivalent of built or hard infrastructure, and is as important for providing services and underpinning socio-economic development. Hence, ecological infrastructure is expected to contribute to functioning as ecological disaster reduction, which is termed Ecosystem-based Solutions for Disaster Risk Reduction (Eco-DRR). Although ecological infrastructure already exists in the landscape, it might be degraded, needs to be maintained and managed, and in some cases restored. Maintenance and restoration of ecological infrastructure is important for security of human lives. Therefore, analytical tool and effective visualization tool in spatially explicit way for the past natural disaster and future prediction of natural disaster in relation to ecological infrastructure is considered helpful. Hence, Web-GIS based Ecological Infrastructure Environmental Information System (EI-EIS) has been developed. This paper aims to describe the procedure of development and future application of EI-EIS. The purpose of the EI-EIS is to evaluate functions of Eco-DRR. In order to analyse disaster data, collection of past disaster information, and disaster-prone area is effective. First, a number of digital maps and analogue maps in Japan and Europe were collected. In total, 18,572 maps over 100 years were collected. The Japanese data includes Future-Pop Data Series (1,736 maps), JMC dataset 50m grid (elevation) (13,071 maps), Old Edition Maps: Topographic Map (325 maps), Digital Base Map at a scale of 2500 for reconstruction planning (808 maps), Detailed Digital Land Use Information for Metropolitan Area (10 m land use) (2,436 maps), and Digital Information by GSI (national large scale map) (71 maps). Old Edition Maps: Topographic Map were analogue maps, and were scanned and georeferenced. These geographical area covered 1) Tohoku area, 2) Five Lakes of Mikata area (Fukui), 3) Ooshima Island (Tokyo), 4) Hiroshima area (Hiroshima), 5) Okushiri Island (Hokkaido), and 6) Toyooka City area (Hyogo). The European data includes topographic map in Germany (8 maps), old topographic map in Germany (31 maps), ancient map in Germany (23 maps), topographic map in Austria (9 maps), old topographic map in Austria (17 maps), and ancient map in Austria (37 maps). Second, focusing on Five Lakes of Mikata area as an example, these maps were integrated into the ArcGIS Online® (ESRI). These data can be overlaid, and time-series data can be visualized by a time slider function of ArcGIS Online.

AN ATTEMPT TO DEVELOP AN ENVIRONMENTAL INFORMATION SYSTEM OF ECOLOGICAL INFRASTRUCTURE FOR EVALUATING FUNCTIONS OF ECOSYSTEM-BASED SOLUTIONS FOR DISASTER RISK REDUCTION (ECO-DRR)

“Ecological Infrastructure (EI)” are defined as naturally functioning ecosystems that deliver valuable services to people, such as healthy mountain catchments, rivers, wetlands, coastal dunes, and nodes and corridors of natural habitat, which together form a network of interconnected structural elements in the landscape. On the other hand, natural disaster occur at the locations where habitat was reduced due to the changes of land use, in which the land was converted to the settlements and agricultural cropland. Hence, habitat loss and natural disaster are linked closely. Ecological infrastructure is the nature-based equivalent of built or hard infrastructure, and is as important for providing services and underpinning socio-economic development. Hence, ecological infrastructure is expected to contribute to functioning as ecological disaster reduction, which is termed Ecosystem-based Solutions for Disaster Risk Reduction (Eco-DRR). Although ecological infrastructure already exists in the landscape, it might be degraded, needs to be maintained and managed, and in some cases restored. Maintenance and restoration of ecological infrastructure is important for security of human lives. Therefore, analytical tool and effective visualization tool in spatially explicit way for the past natural disaster and future prediction of natural disaster in relation to ecological infrastructure is considered helpful. Hence, Web-GIS based Ecological Infrastructure Environmental Information System (EI-EIS) has been developed. This paper aims to describe the procedure of development and future application of EI-EIS. The purpose of the EI-EIS is to evaluate functions of Eco-DRR. In order to analyse disaster data, collection of past disaster information, and disaster-prone area is effective. First, a number of digital maps and analogue maps in Japan and Europe were collected. In total, 18,572 maps over 100 years were collected. The Japanese data includes Future-Pop Data Series (1,736 maps), JMC dataset 50m grid (elevation) (13,071 maps), Old Edition Maps: Topographic Map (325 maps), Digital Base Map at a scale of 2500 for reconstruction planning (808 maps), Detailed Digital Land Use Information for Metropolitan Area (10 m land use) (2,436 maps), and Digital Information by GSI (national large scale map) (71 maps). Old Edition Maps: Topographic Map were analogue maps, and were scanned and georeferenced. These geographical area covered 1) Tohoku area, 2) Five Lakes of Mikata area (Fukui), 3) Ooshima Island (Tokyo), 4) Hiroshima area (Hiroshima), 5) Okushiri Island (Hokkaido), and 6) Toyooka City area (Hyogo). The European data includes topographic map in Germany (8 maps), old topographic map in Germany (31 maps), ancient map in Germany (23 maps), topographic map in Austria (9 maps), old topographic map in Austria (17 maps), and ancient map in Austria (37 maps). Second, focusing on Five Lakes of Mikata area as an example, these maps were integrated into the ArcGIS Online® (ESRI). These data can be overlaid, and time-series data can be visualized by a time slider function of ArcGIS Online.

Characterization of a novel negevirus isolated from Aedes larvae collected in a subarctic region of Japan.

We isolated and characterized a novel positive-sense, single-stranded RNA virus from Aedes larvae collected on Okushiri Island, Hokkaido, Japan. This virus, designated Okushiri virus (OKV), replicated in the Aedes albopictus cell line C6/36 with severe cytopathic effects and produced a large number of spherical viral particles that were 50-70 nm in diameter and released into the cell culture medium. The OKV genome consisted of 9,704 nucleotides, excluding the poly(A) tail at the 3'-terminus, and contained three major open reading frames (ORF1, ORF2, and ORF3). ORF1 encoded a putative protein of approximately 268 kDa that included a methyltransferase domain, FtsJ-like methyltransferase domain, helicase domain, and RNA-dependent RNA polymerase domain. The genome organization and results of a phylogenetic analysis based on the amino acid sequence predicted from the nucleotide sequence indicated that OKV is a member of a new insect virus group of negeviruses with a possible evolutionary relationship to some plant viruses. ORF2 and ORF3 were suggested to encode hypothetical membrane-associated proteins of approximately 45 kDa and 22 kDa, respectively. This is the first study on a novel negevirus isolated from mosquito larvae in Japan.

The role of diffraction effects in extreme run-up inundation at Okushiri Island due to 1993 tsunami

Abstract. The tsunami generated on 12 July 1993 by the Hokkaido–Nansei–Oki earthquake (Mw = 7.8) brought about a maximum wave run-up of 31.7 m, the highest recorded in Japan during the 20th century, near the Monai Valley on the west coast of Okushiri Island (Hokkaido Tsunami Survey Group, 1993). To reproduce the extreme run-up height, the three-dimensional non-hydrostatic model (Flow Science, 2012), referred to here as the NH-model, has been locally applied with open boundary conditions supplied in an offline manner by the three-dimensional hydrostatic model (Ribeiro et al., 2011), referred to here as the H-model. The area of the H-model is sufficiently large to cover the entire fault region with one-way nested multiple domains. For the initial water deformation, Okada's fault model (1985) using the sub-fault parameters is applied. Three NH-model experiments have been performed, namely without islands, with one island and with two islands. The experiments with one island and with two islands give rise to values close to the observation with maximum run-up heights of about 32.3 and 30.8 m, respectively, while the experiment without islands gives rise to about 25.2 m. The diffraction of the tsunami wave primarily by Muen Island, located in the south, and the southward topographic guiding of the tsunami run-up at the coast are, as in the laboratory simulation (Yoneyama et al., 2002), found to result in the extreme run-up height near Monai Valley. The presence of Hira Island enhances the diffraction of tsunami waves but its contribution to the extreme run-up height is marginal.

奥尻島における産業振興への取組み

奥尻島における産業振興への取組み