Collisional disruption experiments of porous targets

More and more small bodies are found to be porous. Laboratory impact experiments of various porous materials have been performed, which increased our understanding of the impact process of porous bodies. In this review, we classify porous targets according to the internal structure, describe the physical properties that characterize these materials, and summarize some results of impact strength and the general tendency upon impact condition and material properties. The material property presented here includes a relation between applied load and distension although measured in static condition. Further investigation is required to clarify the role of crack growth and compaction in the time evolution of physical properties of porous materials upon impact. Laboratory experiments with detailed material properties will be useful as a database that can serve as a reference for numerical modeling and theoretical scaling considerations.     

Logic-tree Approach for Probabilistic Tsunami Hazard Analysis and its Applications to the Japanese Coasts

For Probabilistic Tsunami Hazard Analysis (PTHA), we propose a logic-tree approach to construct tsunami hazard curves (relationship between tsunami height and probability of exceedance) and present some examples for Japan for the purpose of quantitative assessments of tsunami risk for important coastal facilities. A hazard curve is obtained by integration over the aleatory uncertainties, and numerous hazard curves are obtained for different branches of logic-tree representing epistemic uncertainty. A PTHA consists of a tsunami source model and coastal tsunami height estimation. We developed the logic-tree models for local tsunami sources around Japan and for distant tsunami sources along the South American subduction zones. Logic-trees were made for tsunami source zones, size and frequency of tsunamigenic earthquakes, fault models, and standard error of estimated tsunami heights. Numerical simulation rather than empirical relation was used for estimating the median tsunami heights. Weights of discrete branches that represent alternative hypotheses and interpretations were determined by the questionnaire survey for tsunami and earthquake experts, whereas those representing the error of estimated value were determined on the basis of historical data. Examples of tsunami hazard curves were illustrated for the coastal sites, and uncertainty in the tsunami hazard was displayed by 5-, 16-, 50-, 84- and 95-percentile and mean hazard curves.     

Variable Tsunami Sources and Seismic Gaps in the Southernmost Kuril Trench: A Review

In the southernmost Kuril Trench, the tsunami source regions vary their along-trench extent even among earthquakes occurring within the same segment. Recent studies suggest that the tsunami source of the 1952 Tokachi-oki earthquake (M 8.1) differs from but partially overlaps with that of the 2003 Tokach-oki earthquake (M 8.0). Furthermore, the along-trench extent among the earthquakes seems to differ between deep and shallow portions of the subduction interface. A seismic gap has been recognized along the deep subduction interface between the sources of the 1952 and 1973 earthquakes. We propose that the gap is now larger, including both shallow to deep portions of the interface between the 1973 and 2003 earthquakes. Variability in spatial extent of large subduction earthquakes in both along-trench direction and trench-normal direction makes it difficult to forecast future earthquakes in the southernmost Kuril Trench.     

Efficient analysis of pile-group effect on seismic stiffness and strength design of buildings

A new efficient method is developed for the analysis of pile-group effects on the seismic stiffness and strength design of buildings with pile foundations. An efficient continuum model consisting of a dynamic Winkler-type soil element and a pile is used to express the dynamic behavior of the structure-pile-soil system with only a small numerical error. The pile-group effect is taken into account through the influence coefficients among piles which are defined for interstory drifts and pile-head bending moments. It is shown that, while the pile-group effect reduces the interstory drift of buildings in general, it may increase the bending moment of piles at the head. This means that the treatment without the pile-group effect results in the conservative design for super-structures and requires a revised member design for piles.     

Velocity of finer fragments from impact

We describe the method and the result of a new experiment to obtain velocity distribution of fine ejecta fragments, from a few to a hundred microns in size, produced from basalt targets by impacts of nylon projectiles at a velocity of 3.7 km s⁻¹. The size distribution of holes perforated by the ejecta fragments on thin films and foils placed around the targets was investigated, and the size-velocity relation was determined with the aid of an empirical formula for threshold penetration (McDonnell and Sullivan, Hypervelocity Impacts in Space, Unit for Space Sciences, University of Kent, 1992). The velocity of the fastest fragments, at a given size, is from the extrapolation of the size-velocity relation for 1–100 mm fragments (Nakamura and Fujiwara, Icarus92, 132–146, 1991; Nakamura et al, Icarus100, 127–135, 1992). The laboratory results are also compared with those obtained from the study of secondary craters around large lunar craters (Vickery, Icarus67, 224–236, 1986, Geophys. Res. Lett. 14, 726–729, 1987). All these data provide a smooth size-velocity relationship in the normalized fragment size range of four orders of magnitude.     

A survey of possible impact structures on 25143 Itokawa

We determined the morphologies and dimensions of possible impact craters on the surface of Asteroid 25143 Itokawa from images taken by the Hayabusa spacecraft. Circular depressions, circular features with flat floors or convex floors, and circular features with smooth surfaces were identified as possible craters. The survey identified 38 candidates with widely varying morphologies including rough, smooth and saddle-shaped floors, a lack of raised rims and fresh material exposures. The average depth/diameter ratio was 0.08±0.03: these craters are very shallow relative to craters observed on other asteroids. These shallow craters are a result of (1) target curvature influencing the cratering process, (2) raised rim not being generated by this process, and (3) fines infilling the craters. As many of the crater candidates have an unusual appearance, we used a classification scheme that reflects the likelihood of an observed candidate's formation by a hypervelocity impact. We considered a variety of alternative interpretations while developing this scheme, including inherited features from a proto-Itokawa, spall scars created by the disruption of the proto-Itokawa, spall scars following the formation of a large crater on Itokawa itself, and apparent depressions due to random arrangements of boulders. The size-frequency distribution of the crater candidates was close to the empirical saturation line at the largest diameter, and then decline with decreasing diameter.     

Prediction of ground motion in the Osaka sedimentary basin associated with the hypothetical Nankai earthquake

We studied the long-period ground motions in the Osaka sedimentary basin, Japan, which contains a 1- to 3-km thickness of sediments and is the site of many buildings or construction structures with long-natural period. We simulated the broadband ground motions likely to be produced by the hypothetical Nankai earthquake: the earthquake expected to give rise to the most severe long-period ground motion within the basin. For the simulation, we constructed multiscale heterogeneous source models based on the Central Disaster Management Council of Japan (CDMC) source model and adopted a hybrid computation method in which long-period motion and short-period motion are computed using a 3-D finite difference method and the stochastic Green’s function method, respectively. In computing long-period motions, we used a 3-D structure model of the crust and the Osaka sedimentary basin. The ground motions are estimated to have peak velocities of 50–90 cm/s, prolonged durations exceeding 300 s, and long predominant periods of 5–10 s in the area with great thickness of sediments. The predominant periods are in agreement with an approximate evaluation by 4 H/V _s where H and V _s are the thickness of the sediment and the average S wave velocity, respectively.     

Impact of mercury emissions from incineration of automobile shredder residue in Japan

Mercury emissions from the incineration of automobile shredder residues (ASRs) were investigated. Continuous monitoring of elemental and reactive gaseous Hg in flue gas was performed in lab-scale and plant-scale ASR incineration. Results of continuous monitoring agreed with those obtained using the JIS K0222 method and Ontario-Hydro method. Before cleaning by air pollutant control devices (APCDs), reactive Hg was the dominant form of that element in both lab-scale and plant-scale results. Emission factors of reactive Hg before APCDs estimated from monitoring results showed large differences between plant-scale and lab-scale emissions. The emission factor in the plant scale was more than 10 times larger than that in the lab-scale, which is explainable by the different Hg contents of ASR. Based on plant-scale monitoring at the stack, emission factors after APCDs were estimated as 0.79 mg-Hg/Mg-ASR for elemental Hg and 6.8 mg-Hg/Mg-ASR for reactive Hg. Using these emission factors, total Hg emissions from ASR incineration were estimated as 2.2 kg/a. An ASR incineration plant investigated in this study used highly effective APCDs. Consequently, these emission factors might result in underestimation of national Hg emissions from ASR incineration. Emission factors estimated from lab-scale monitoring at a fabric filter outlet side might be more appropriate. However, even if emission factors calculated from plant-scale or the lab-scale monitoring are used, estimated emissions are still less than 1.0% of total Hg emissions in Japan. Therefore, Hg emissions from ASR incineration can be evaluated as insignificant. Unless Hg contents of ASR increase extremely, ASR incineration would be a minor source of Hg atmospheric emission in Japan, even if all ASRs were incinerated.     

Scale mismatches and their ecological and economic effects on landscapes: A spatially explicit model

Mismatches between the spatial scales of human decision-making and natural processes contribute to environmental problems such as global warming and biodiversity losses. People damage the environment through local activities like clearing land or burning fossil fuels, but the damages only become manifest at larger regional or global scales where no one pays for them. Payments for ecological services like carbon sequestration can correct for these damages caused by scale mismatches. This paper presents a spatially explicit land-use model to investigate the consequences of scale mismatches for pollination and carbon storage services and examine the effect of payment for only carbon storage services. The model integrates processes in multiple spatial scales ranging from the parcel level used by landowners’ decision about deforestation, to the larger scale used by animals to pollinate plants, and finally to the global scale where carbon storage services are supplied. We show that payment for carbon storage services can become an effective mechanism to protect forests at the same time that it creates inequities among landowners in income level.These findings suggest that market-based approaches that focus on conservation of a single ecosystem service may reproduce unequal power relations among landowners.