Showing papers by "Shin Yabushita published in 1994"

Are periodicities in crater formations and mass

Abstract: Periodicities in crater formation rate and mass-extinctions are reviewed. The former exhibits a period of 30 million yr, while the latter appear to have a periodicity at 26 myr. Results obtained earlier that small craters better satisfy the adopted criterion for statistical testing is shown due to the fact that there is a strong clustering of small craters in a recent past (<10 myr). On the basis of the dataset of craters compiled by Grieve, it is shown that there are several craters for which no mass extinctions correspond. The difference in the periods of the craters and of mass extinctions and the lack of mass extinctions that correspond to large craters appear to suggest that the two periodicities are not interrelated, and large impacts merely act as triggers for the mass-extinctions; the only exception being theK/T boundary.

On the possible hazard on the major cities caused by asteroid impact in the Pacific ocean

Abstract: Semi-quantitative investigation is made of hazard expected from an asteroidal impact in the Pacific. An impact ofd (diameter) = 200 m asteroid has a probability of hitting somewhere in the Pacific once in 15000 y. By carrying out a Monte Carlo simulation, such an impact, on average, is shown to create a tsunami as high as 16, 14, 15, and 21 m at Japan, Taiwan, Shanghai and Hawaii, respectively. Wooden houses, stone and brick houses, and reinforced concrete buildings are likely to be demolished by tsunamis of height 2, 7 and 20 m respectively. Thus, there is a probability of 1% or so that most of the artificial constructions on the coast lines of the Pacific be destroyed in the next century by an asteroidal impact.