Kazuhisa Goto

A numerical model for the transport of a boulder by tsunami

[1]xa0We have conducted hydraulic experiments in an open channel with cubic and rectangular shaped solid blocks on the slope for investigating the boulder transport process by tsunami. In our experiments, the block was mainly seen to be transported by a bore due to rolling or saltation rather than by sliding. Previous models for the boulder transport by tsunamis assumed sliding as a mode of transport for the boulder. Therefore, these models underestimated the distance of the boulder moved by the tsunami when it was transported due to rolling or saltation. In this study, we have developed a practical model for the transport of a boulder by tsunami, which takes into account the various transport modes. We introduce an empirical variable coefficient of friction by assuming that the coefficient decreases with decrease in ground contact time when the block was transported by rolling or saltation. With the aid of this parameter, the model can explain various modes of transport, i.e., sliding, rolling, and saltation, and reproduces the experimental results well. We further applied this improved model to a tsunami boulder at Inoda area in Ishigaki Island, Japan, which was transported by the 1771 Meiwa tsunami. The calculated distance of transport of the boulder was approximately 650 m, which is consistent with the description in the historical document. Based on our calculations, we estimated hydraulic values of the tsunamis. Estimation of such hydraulic values is important for understanding the behavior and power of the historical tsunamis, besides aiding future disaster mitigation efforts.

The 2011 Tohoku-oki Earthquake Tsunami: Similarities and Differences to the 869 Jogan Tsunami on the Sendai Plain

A post-tsunami field survey following the 2011 Tohoku-oki Earthquake Tsunami was carried out to asses inundated area in Sendai Plain, Northeast Japan. The type of inundation was classified into two categories (major and minor) according to the amount of accumulated debris, garbage and sediment. Major and minor inundations were identified up to 4 and 5xa0km from the coastline, respectively. Many artificial geomorphological features, such as roadway embankments and canals, were believed to have affected the run-up process of the tsunami. The inundation area of the 2011 tsunami on the Sendai Plain is compared with that of the 869 Jogan tsunami, which was reconstructed using numerical modeling based on available historical and geological records. The inundation area of the 2011 Tohoku-oki tsunami is comparable to that of the 869 Jogan tsunami, although a direct comparison is difficult due to differences in geomorphological contexts between the paleo period and the present.

Field measurements and numerical modeling for the run-up heights and inundation distances of the 2011 Tohoku-oki tsunami at Sendai Plain, Japan

We conducted an urgent field survey at the Sendai Plain to measure the run-up heights and inundation distances of the 2011 Tohoku-oki tsunami. We used GPS measurements because of the remarkably long inundation distances (ca. 5.4 km). We established an accurate measurement scheme using the far electric reference points (about 350 km). Using this method, we quickly measured 69 run-up heights within 3 days. The tsunami run-up heights and inundation distances varied mainly according to the local topography, ranging from 9.6 m at 0.4 km to 0.2 m at 5.4 km, respectively. Furthermore, artificial structures and topography played an important role in constraining the inundation limit. Our observations are important for future analyses using aerial and satellite imagery and numerical modeling in the area because the maximum inundation area might be underestimated in the images as a result of the subtle traces of the tsunami inundation, which were difficult to identify in the field. However, results show that numerical modeling might not reproduce minor inundation beyond the highway without sufficiently high-resolution topographic data because data for the modeling are usually rough, and the highway, small channels, and street gutters, which played an important role in local inundation, are too small a resolution to be recognized in the model.

Tsunami recurrence revealed by Porites coral boulders in the southern Ryukyu Islands, Japan

Information about past tsunami hazards, such as their recurrence interval and magnitude, is needed for future disaster prediction and mitigation. We examined radiocarbon ages of the surfaces of massive coral boulders cast ashore by past tsunamis in the southern Ryukyu Islands, Japan, where few historical and geological records of past tsunamis are available. We selected only non-eroded Porites coral boulders along the shoreline, because their characteristics make it possible to determine the probable timing of their deposition by tsunamis, and we applied a dating method that uses the cumulative probability distributions of large numbers of radiocarbon measurements of those boulders to determine the timing of past tsunamis. The results demonstrate that the southern Ryukyu Islands have repeatedly experienced tsunami events since at least 2400 yr ago, with a recurrence interval of ∼150–400 yr. The largest Porites tsunami boulder that we studied (long axis, 9 m), which is probably the largest single-colony tsunami boulder in the world, was displaced by the A.D. 1771 Meiwa tsunami. Although the 1771 Meiwa tsunami was likely the largest event in at least the past 700 yr, calculations of current velocity show that all identified tsunamis occurring before 1771 were probably large enough to cause considerable damage to human-built structures and loss of life. This study demonstrates that by reliably dating large numbers of selected coastal boulders it is possible to ascertain the timing, recurrence interval, and magnitude of past tsunamis in a location where few adequate survey sites of sandy tsunami deposits exist.

Complex tsunami waves suggested by the Cretaceous-Tertiary boundary deposit at the Moncada section, western Cuba

The Moncada Formation in western Cuba is an 2-m-thick weakly metamorphosed complex characterized by repetition of calcareous sandstone units that show overall upward fining and thinning. The Moncada Formation contains abundant shocked quartz, altered vesicular impact-melt fragments, and altered and deformed greenish grains of possible impact glass origin. In addition, a high iridium (0.8 ppb)

Thermal cracking of coal model diaryl ethers in aromatic solvent

Abstract Thermal cracking of nine diaryl ethers in a hydrogen donor solvent or 1-methylnaphthalene was studied kinetically. The rate of conversion of the diaryl ethers was first order with respect to the substrate concentration and increased with increase in size of the aryl structure. The relative rate constant of aryloxygen bond cleavage calculated on the basis of first order reaction has indicated that the ease of cracking depends strongly on the aromatic structure and the position of substitution. The conversion rate of 2, 2′-dinaphthyl ether was remarkably enhanced in the presence of hydrogen donor solvent, for example by a factor of ten in the presence of 9, 10-dihydroanthracene. The activation energy of thermal conversion of 2, 2′-dinaphthyl ether was 214 kJ/mole in methylnaphthalene, 151 kJ/mole in tetralin and 88 kJ/mole in dihydroanthracene. The enhancing effect of the hydrogen donor was considered due to hydrogen transfer to the aromatic nucleus of the diaryl ether from the hydrogen donor and successive fast decomposition of hydrogenated ethers.

Cretaceous-Tertiary boundary sequence in the Cacarajicara Formation, western Cuba: An impact-related, high-energy, gravity-flow deposit

The Cacarajicara Formation of western Cuba is a more than 700 m thick calcareous clastic sequence that contains shocked quartz throughout, and spherules. Three members are recognized. The lower member consists of limestone and chert boulders, and disconformably overlies Cretaceous deep-water turbidite. It is characterized by: (1) a grain-supported fabric with only a small amount of matrix, (2) 5–15 cm, wellsorted clasts and occasional boulders, (3) reversely graded, discoidal or rectangular boulders showing a preferred orientation, (4) abundant shallowand deep-water carbonate clasts in a well-mixed fabric, (5) direct contact between adjacent clasts, and (6) hydrostatic deformation within a black clay matrix. This evidence suggests that the lower member was deposited under conditions of high-density and high-speed laminar flow. The middle member consists of upward graded, massive to well-bedded, homogeneous calcarenite. Unusual fluid-escape structures in the thick calcarenite suggest that this member formed by high-density turbidity suspension. The upper member consists of fine calcarenite mudstone; there is no evidence of bioturbation. We infer that it was deposited from a dilute, low-density suspension. Kiyokawa, S., Tada, R., Iturralde-Vinent, M., Masui, T., Tajika, E., Gracia Delgado, D., Oji, T., Nakano, Y., Goto, H., Takayama, H., and Rojas-Consuegra, R., 2002, More than 700-m-thick Cretaceous-Tertiary boundary sequence of the Cacarajicara Formation, western Cuba; Ejecta induced high-energy flow deposit, in Koeberl, C., and MacLeod, K.G., eds., Catastrophic Events and Mass Extinctions: Impacts and Beyond: Boulder, Colorado, Geological Society of America Special Paper 356, p. 125–144. S. Kiyokawa et al. 126 On the basis of these criteria, the Cacarajicara Formation is interpreted to be a single hyperconcentrated flow that was formed by high-energy and high-speed concentrated flow. The south-southeast paleocurrent direction suggests that this highenergy flow originated on the Yucatan platform and was triggered by the Chicxulub impact. We propose that a gigantic flow deposit was induced by earthquake-generated collapse of the Yucatan platform margin owing to ballistic flow from the Chicxulub impact.

Impact of Tsunami Inundation on Soil Salinisation: Up to One Year After the 2011 Tohoku-Oki Tsunami

The long-term effect of tsunami inundation on soil salinisation was assessed following the 2011 Tohoku-oki tsunami in two areas on the Sendai Plain, near Sendai airport in the Miyagi Prefecture and Matsukawa-ura near Soma in the Fukushima Prefecture. Data gathered over four sampling seasons 2, 5, 9 and 11 months after the tsunami near Sendai airport show that the salt content generally decreased with time. Concentrations were nevertheless higher in February 2012 than in October 2011, probably due to capillary action and evaporation following long periods with little precipitation in the winter, while the lower concentrations in October were attributed to dilution due to intense rainfall prior to the sampling period. In February 2012, the area with chloride concentrations over the guidelines for the establishment of rice seedlings still extended for nearly 1 km between 2.45 and 3.33 km inland. Chloride concentrations also reached the guideline values at the land surface 1.71 km inland. This corresponded to the limit of the area deemed not suitable for rice production by local rice farmers. However, recent observations revealed that rice crops were not only halted in 2011 but also in 2012, probably due to high salinisation of soil and/or surface and groundwater. Our study shows that soil salinisation was still recorded to nearly 15 cm depth in areas with fine-grained organic-rich soil ~2.5 km from the shoreline 11 months after the tsunami, and that water-leachable ions were preferentially retained in organic-rich muddy sediment and soil, reflecting the long-term impact of tsunami inundation. In Matsukawa-ura, salt crusts still covered the area flooded by the tsunami in February 2012 and both the soil and muddy tsunami deposit were characterised by high chloride and sulphate concentrations. The latter might also lead to sulphide toxicity. Remediation measures have been implemented in certain areas, but further research needs to be carried out to test the effectiveness of the measures being used to allow rice production to resume.

Size and spatial distributions of fault populations: Empirically synthesized evolution laws for the fractal geometries

[1]xa0We performed fractal analysis for 10 fault populations that are developed in continuous outcrops of Neogene sedimentary rocks. A transect line was set with reference to the principal stress axes, and the position and displacement of all faults that intersect the transect line were measured precisely. We found that both the fractal dimension of the size (net slip) frequency and that of the spatial distribution of fault displacements are determined by only two parameters: an input energy density and a dissipative energy density. These two kinds of fractal dimension evolve (decrease) as the ratio of the input energy to the dissipative energy increases, and are tied by a universal equation.

Re-evaluation of the 1771 Meiwa Tsunami Source Model, Southern Ryukyu Islands, Japan

The 1771 Meiwa Tsunami, which was generated on 24 April 1771, struck the Miyako–Yaeyama Islands located in the southern part of the Ryukyu Islands, Japan. It was one of the most devastating tsunamis ever to hit Japan. Based on historical documents and recent field surveys, the run-up heights at some areas of the Miyako–Yaeyama Islands were estimated as up to 30 m at Ishigaki Island, although it is noteworthy that the extremely high run-up heights were only observed at the southeastern coast of the island and those in other areas were generally lower than 10–15 m. Based on these run-up heights, several tsunami source models have been proposed. However, the model remains controversial because the actual fault, the putative tsunami source, has not been identified. For this study, we conducted numerical calculations to test the tsunami source models. We used reliable observed run-up heights including newly available data around the Miyako Islands as well as the high-resolution bathymetric data with reef topography. By comparing estimated and calculated run-up heights, we tested the validity of the previously proposed models as well as that of our own. Results showed that the tsunami generated by the reverse dip–slip intraplate fault plus the subsequent occurrence of a submarine landslide offshore from southeastern Ishigaki Island is the preferred model because it reproduces the historically documented run-up heights well. In particular, this model explains unusually high run-up heights at the southeastern coast of Ishigaki Island as a result of the local effect of the submarine landslide. Possible evidence of some landslides has been found in this area, but a detailed submarine survey is necessary to confirm the source model and to find evidence of the submarine landslide generated by the 1771 earthquake.