Okushiri Island Research Articles

Advanced numerical modelling of tsunami wave propagation, transformation and run-up

This paper presents a series of numerical models tests performed to assess the ability of the OpenFOAM® modelling system to represent the physics that stands behind the propagation of tsunami waves in coastal regions and in particular their transformation (by means of shoaling, refraction, reflection) over uneven bathymetries and their interaction with the shoreline (run-up, run-down, breaking). A series of tests is selected from the literature to explore the accuracy, applicability and limitations of this particular computational fluid dynamics model solving the three-dimensional Navier–Stokes equations for incompressible multiphase fluids. The range of scenarios tested includes experimental work on wave propagation over shoals, solitary wave run-up and the Monai valley tsunami physical model test recreating the Hokkaido–Nansei–Oki 1993 tsunami that struck Okushiri Island, Japan. This allowed direct comparison with experimental data from physical model tests as well as with other established two-dimensional – that is, depth integrated – and three-dimensional numerical models.

Repeated magmatism at 34Ma and 23-20Ma producing high magnesian adakitic andesites and transitional basalts on southern Okushiri Island, NE Japan arc

Abstract The southern part of Okushiri Island in the present-day back-arc margin of the NE Japan arc is one of the rare convergent plate boundaries where similar magma types (high-magnesian adakitic andesite (HMAA) and high-TiO 2 basalt (HTB)) have been erupted concurrently at more than one time. Oligocene HMAA can be divided into two types: HMAA-I is characterized by high Sr/Y and low Y, and HMAA-II by relatively low Sr/Y and high Y. HMAA-I is primitive in terms of MgO (8.5 wt.%), Mg# (67), Ni (232 ppm) and Cr (613 ppm) contents, and the most Mg-rich olivine phenocrysts plot within the mantle olivine array in terms of Fo and NiO. The similar Cr versus Ni relations of types I and II HMAA indicate some interaction of slab-derived adakitic melts with mantle peridotite, whereas Ni contents are higher than those of most boninites derived by partial melting of mantle peridotite at a given Cr content. Types I and II HMAA have more enriched Sr and Nd isotopic compositions than N-MORB. The petrography and geochemistry of these rocks, combined with published results on the genesis of high-magnesian andesite (HMA) indicate that types I and II HMAA could be produced by interaction of slab (N-MORB and sediment)-derived adakitic melts with mantle peridotite. The comagmatism of HMAA and HTB is ascribed to the following model. A cool, less hydrous, adakite magma (spherical diapir) would rise from the subducting slab (Pacific Plate) and become more hydrous as a result of its interaction with overlying hydrous peridotite. This hydrated adakitic diapir further ascends and is heated on entering the overlying mantle wedge. Subsequently, the temperature and H 2 O gradients in the ascending adakitic diapir and surrounding mantle peridotite would have been established. The HTB magma segregated from the surrounding mantle peridotite region (high temperature and low H 2 O content) at a depth of 60 km or more, whereas the adakitic diapir (low temperature and high H 2 O content) continued to rise, with its chemical composition modified due to interaction with the surrounding mantle peridotite. Type I HMAA then segregated at about 50 km. The most attractive tectono-magmatic model to account for production of adakitic magma at two different periods in the same cool subduction zone region involves upwelling of depleted hot asthenosphere into the subcontinental lithosphere beneath the back-arc margin of the NE Japan arc, coincident with back-arc rifting which took place at the initiation of the Japan Sea opening. The unusually high temperature conditions established in the mantle wedge due to upwelling of depleted hot asthenosphere caused partial melting of a limited part of the cool oceanic crust subducting beneath the NE Japan arc, resulting in the generation of adakitic magma.

Land–Water Boundary Treatment for a Tsunami Model With Dimensional Splitting

A numerical model for tsunami simulations Cliffs is exercised with the complete set of NTHMP-selected benchmark problems focused on inundation, such as simulating runup of a non-breaking solitary wave onto a sloping beach, runup on a conical island, a lab experiment with a scaled model of Monai Valley, and the 1993 Hokkiado tsunami and inundation of the Okushiri Island.

Tsunami deposits in Okushiri Island, southwestern Hokkaido, Japan

Tsunami deposits in Okushiri Island, southwestern Hokkaido, Japan

Petrology study of pyroclastic rocks of Yoneoka formation, Okushiri island, southwest Hokkaido

Petrology study of pyroclastic rocks of Yoneoka formation, Okushiri island, southwest Hokkaido

日本海MD179コアに見られる海氷起源の砕屑物に関する研究

A large number of ice-rafted debris (IRD) have been found in the MD179 cores of the Japan Sea from off Joetsu to off Okushiri Island. The IRD appear in the MIS 5.4 when the last inter-glacial period passed, and occur most abundantly during the MIS 2. The occurrence of IRD in the sediments of off Joetsu indicates floated ice had commonly appeared in the further southern part of the Japan Sea than the area the former studies have expected.Basalt lava is the most common lithology among the collected IRD, and black siliceous mudstone or chert follow it. The roundness of IRD reveals the IRD-bearing ice was not originated from on-land glacier but from sea ice formed on sea shore. The sea ice has been expected to come from southern part of the Sikhote-Alin area of the Asian Continent across the Japan Sea (Ikehara, 2003), but the lithology of IRD indicates the coast along the Japanese Islands is not precluded from the provenance area. The high frequency of IRD in the sediment of off Joetsu during the MIS 2 strongly suggests the floated ice had arrived in the further southern part of the Japan Sea. The formation and melting of sea ice in a wide area of the Japan Sea should have had a great influence on the environment of the Japan Sea and the surrounding land areas.

Capacity Planning and Economical Evaluation of a Renewable Power System for Remote Island

This paper presents capacity planning and economical evaluation of a renewable power system proposed for Okushiri Island, which is a remote island in the southwest of Hokkaido. In this system, the power demand is mainly provided by photovoltaic, wind turbine. Batteries are used as short time energy storage, and a hydrogen storage system (composed of water electrolyzer, hydrogen storage, and fuel cell) is used as long time energy storage. Optimal capacities of these power sources are those meet the required supply reliability, with the lowest cost. As the first step in the capacity planning, mathematical models for characterizing components are explained. The second step is to optimize the capacities of components. The configurations, which meet the required supply reliability with the lowest cost, give the optimal choices. These calculations are carried out with hourly meteorological data and energy demand data of Okushiri Island. As a result, hybrid storage (battery and hydrogen) is the best choice for Okushiri Island when high supply reliability is required. In the range of loss of power supply probability 0.1 to 0, the levelized cost of energy will be about 70-150yen/kWh.

Origin of Late Oligocene to Middle Miocene Adakitic Andesites, High Magnesian Andesites and Basalts from the Back-arc Margin of the SW and NE Japan Arcs

Late Oligocene to Middle Miocene adakitic andesites are found in the southern part of Okushiri Island, the northern Noto Peninsula and in the Toyama region in the present-day back-arc margin of the SW and NE Japan arcs. On Okushiri Island, adakitic andesite is accompanied by moderately alkaline basalt, whereas on the Noto Peninsula, adakitic andesite has been erupted along with high magnesian andesite (HMA), bronzite andesite and tholeiitic basalt. Adakitic andesites from all three locations are characterized by high Sr/Y and low Y, and have higher MgO contents than adakitic melts generated by experimental melting of metabasalt and amphibolite. They also have higher Ni and Cr contents than either Archaean tonalite–trondhjemite–granodiorite (TTG) suites or Early Cretaceous adakitic granites, which have been attributed to partial melting of subducted oceanic crust. The Noto Peninsula adakitic andesite has Sr and Nd isotopic compositions identical to normal mid-ocean ridge basalt (N-MORB), whereas the Okushiri Island and Toyama adakitic andesites are more isotopically primitive than N-MORB. The Noto Peninsula primary adakitic melt was derived from subducted oceanic N-MORB crust, whereas the Okushiri Island and Toyama primary adakites are interpreted as melts of subducted N-MORB and sediment that have subsequently interacted with the overlying mantle wedge peridotite. To explain the comagmatism of adakite, HMA and basalt, the following model is proposed. A hydrated adakitic diapir ascends from the subducting slab and is heated because it enters the overlying hot mantle wedge. The subsequent establishment of thermal and H2O gradients in the adakitic diapir and surrounding mantle wedge peridotite results in concurrent generation of adakitic andesite magma in the inner adakitic diapir region (low temperature and high H2O content), HMA and bronzite andesite magmas in the intermediate peridotite region (intermediate temperature and H2O content), and tholeiitic basalt magma in the outer peridotite region (high temperature and lower H2O content). Comagmatic adakite and mildly alkaline basalt are found in cooler and wetter adakitic diapirs and hotter and drier peridotite regions respectively. The most likely tectono-magmatic situation for the genesis of adakitic magmas in this example of a cool subduction zone involves upwelling of hot asthenosphere into the subcontinental lithosphere beneath the back-arc side of the NE Japan arc and northern end of the SW Japan arc, during the period spanning the pre-Japan Sea opening to syn-opening stages. The unusually high temperature conditions established in the mantle wedge owing to upwelling of hot asthenosphere caused partial melting of the relatively cool subducting Pacific plate, resulting in the generation of adakitic magmas.

Mode of Occurrence and Hydration of Glassy Rhyolite Lava from Katsuma-Yama Volcano, Okushiri Island, Hokkaido, Northern Japan

Mode of Occurrence and Hydration of Glassy Rhyolite Lava from Katsuma-Yama Volcano, Okushiri Island, Hokkaido, Northern Japan

Validation and Verification of a Numerical Model for Tsunami Propagation and Runup

A robust numerical model to simulate propagation and runup of tsunami waves in the framework of non-linear shallow water theory is developed. The numerical code adopts a staggered leapfrog finite-difference scheme to solve the shallow water equations formulated for depth-averaged water fluxes in spherical coordinates. A temporal position of the shoreline is calculated using a free-surface moving boundary algorithm. For large scale problems, the developed algorithm is efficiently parallelized employing a domain decomposition technique. The developed numerical model is benchmarked in an exhaustive series of tests suggested by NOAA. We conducted analytical and laboratory benchmarking for the cases of solitary wave runup on simple beaches, runup of a solitary wave on a conically-shaped island, and the runup in the Monai Valley, Okushiri Island, Japan, during the 1993 Hokkaido-Nansei-Oki tsunami. In all conducted tests the calculated numerical solution is within an accuracy recommended by NOAA standards. We summarize results of numerical benchmarking of the model, its strengths and limits with regards to reproduction of fundamental features of coastal inundation, and also illustrate some possible improvements.

Numerical simulations of the coastal effects of tsunami waves caused by the 1993 Hokkaido-Nansei-Oki earthquake

Generally, tsunami waves become hazardous only when approaching the coast. Studying the runup and inundation of tsunami waves is important for understanding the tsunami evolution and for tsunami hazard assessment. Here, we simulated the 1993 Hokkaido-Nansei-Oki (HNO) tsunami using a finite-difference model based on nonlinear shallow-water equations. We focused on the runup and inundation of tsunami wave propagation onto coastal area of Okushiri Island near Hokkaido, Japan, and investigate the relationship of different runup heights with the morphology and bathymetry of the seashore. In the simulation, a nested 4-layer grid system and moving boundary technique are adopted to study runup and inundation. The calculated tsunami heights and inundations in the region agreed well with field measurements. The local bathymetric and topographic characteristics had a first-order effect on the runup. Numerical experiments show that the focusing of certain local bathymetric features would amplify both wave height and current velocity remarkably. The results show that computation on dense grids is necessary to reproduce the observed runup heights, and inundation velocity is an important factor preventing tsunami devastation. In addition, we discussed the potential capability of sediment transport to illustrate the impact of tsunami waves on coastal geomorphology.

DAMAGE AND RECONSTRUCTION OF LIFELINES IN PHANG NGA PROVINCE, THAILAND AFTER THE 2004 INDIAN OCEAN EARTHQUAKE AND TSUNAMI

The Indian Ocean earthquake and tsunami occurred in December 2004 caused destructive damage to Phang Nga Province, Thailand. We carried out two times of interview surveys about 1 and 3 years after the event to administrative bodies and lifeline companies for getting the information on lifeline damage, restoration and reconstruction situation, and summarized the basic concept of reconstruction plan of tsunami suffered towns considering lifeline restoration. On the other hand, as for the comparison of reconstruction problems, the lifelines recovery is reviewed at Aonae district in Okushiri Island after the 1993 Hokkaido-Nansei-oki earthquake. As the result, the difference of the process of reconstruction of town and lifelines has been revealed and the importance of preparing of the reconstruction plan before the event under the consideration of a long-term city planning is pointed out.

Effects of Straits as Dispersal Barriers for the Flightless Roving Carrion Beetle,Silpha perforata(Coleoptera, Silphidae, Silphinae)

Population genetic analyses were conducted for the flightless beetle Silpha perforata in northern Japan to evaluate effects of straits as dispersal barriers. In all, 19 populations on the Hokkaido mainland and one population on each of seven adjacent islands were included in the study. Based on partial sequences (853 bp) of the mitochondrial ND2 gene from 365 individuals, we calculated haplotype diversity (h), nucleotide diversity (pi), Tajima's D, and Fu's F(s) statistics for each population. The genetic distance d(A) and fixation index F(ST) were then estimated between populations, excluding two mainland and two island populations with small sample sizes. The results showed that four island populations (Rebun, Rishiri, Yagishiri, and Teuri) were genetically diverged and isolated from mainland populations, including the closest ones, consistent with the assumption that the straits separating these islands from the mainland have functioned as strong barriers against beetle dispersal. However, some factors other than sea barriers may have resulted in the observed divergence of these island populations, since the straits might be too young to permit such divergence (all are estimated to have been finally established approximately 11,000 to 13,000 years BP). On the other hand, the population on Okushiri Island showed little genetic divergence from the nearest mainland population, suggesting current overseas dispersal across the strait (estimated to have been formed more than 200,000 years BP). The present study thus demonstrated that the effects of straits on dispersal can be diverse, even for species of terrestrial invertebrates with limited dispersal ability.

Detecting Tsunami Affected Area using Satellite SAR Imagery

Using a capability of SAR(Synthetic Aperture Radar) image analysis, the authors develop a method for mapping tsunami affected area, focusing on the relationship the backscattering features between pre and post-event SAR images. The method was applied to Aonae district in Okushiri island which was the most devastated by the 1993 Hokkaido Nansei-oki earthquake tsunami (Okushiri tsunami) to identify the the severity of structural damage with a fragility curve of pre-post SAR image features and probability of structural destruction.

Damage and Reconstruction at Okushiri Town Caused by the 1993 Hokkaido Nansei-Oki Earthquake Tsunami

The Hokkaido Nansei-Oki Earthquake Tsunami that struck Okushiri Island off western Hokkaido, Japan's northeasternmost island in 1993 killed about 200 in Okushiri Town, which had a population of less than 4,000. Damage totaling over yen 66 billion was a severe blow to the community, which had an annual budget of only yen 5 billion. The tsunami was caught by the island and struck the Aonae district on the southern tip from both the west and east. Based on an experience from tsunami in 10 years earlier, it was thought that a tsunami would arrive more slowly than this one did, which increased the human toll. Fire caused by the tsunami increased losses. Among reconstruction efforts, remarkable are an artificial ground and cordial assistance based on monetary donation.

Forest types in Ooiwaoi watershed, Okushiri Island, Hokkaido

Forest types in Ooiwaoi watershed, Okushiri Island, Hokkaido

Embodying Okhotsk Ethnicity: Human Skeletal Remains from the Aonae Dune Site, Okushiri Island, Hokkaido

This article describes human skeletal remains from the Aonae Dune site, Okushiri Island, Hokkaido, Japan. Skeletal remains of an adult female and two subadults were excavated in 2002. Although these remains derived from Okhotsk culture contexts, analyses of cranial and tooth crown measurements demonstrated that Aonae Dune No. 1 (the adult female), Aonae Dune No. 2 (a child of about 11 years), and Aonae Dune No. 3 (a child of about 6 years) are morphologically closer to Epi-Jōmon or Jōmon and Ainu populations and significantly different from other Okhotsk samples in Hokkaido. It is argued that these three skeletons probably represent individuals from a different culture who were adopted into Okhotsk society.

Eruption Products and Structure of Katsuma-Yama Volcano, Okushiri Island, Hokkaido, Northern Japan

Eruption Products and Structure of Katsuma-Yama Volcano, Okushiri Island, Hokkaido, Northern Japan

マルチエージェントシステムを用いた津波からの避難シミュレーション : 奥尻島青苗地区を例として

The simulation model of evacuation behavior from tsunami is constructed utilizing Multi-Agent-System in this study. The validity of the simulation model is verified by applying it to the case of Aonae, Okushiri Island during the 1993 Southwest-off Hokkaido Earthquake. And results of some case studies on current Aonae show that the improvement of evacuating environment affects evacuation behavior greatly, and that moving speed and earlier starting of evacuation are important parameters to minimize total mortality and missing rate.

O-45 北海道奥尻島,漸新世〜前期中新世の高TiO_2高P_2O_5玄武岩及び高MgO高Sr/Y安山岩の岩石学的特徴(6. 環日本海・オホーツク海の火成活動とテクトニクス,口頭発表,一般講演)

O-45 北海道奥尻島,漸新世〜前期中新世の高TiO_2高P_2O_5玄武岩及び高MgO高Sr/Y安山岩の岩石学的特徴(6. 環日本海・オホーツク海の火成活動とテクトニクス,口頭発表,一般講演)