Kazuya Iida

In this study, we focused on inudation forecasting of topography, and examined how 3DCG and physical model teaching materials affect the understanding topography. The following three findings were obtained from the results of classroom practice using 3DCG and physical model teaching materials. The first is the effect of using only 3DCG or physical models on the understanding of topography. Statistical analysis showed that for characteristic landforms such as valleys and plateaus, both teaching materials were significantly more accurate in predicting inundation than 2D topographic maps. The second point is the effect of combining the 3DCG teaching materials and the physical model teaching materials. The mean number of correct responses to inundation forecasts for microtopographic features such as depressions on a plateau was significantly higher when both materials were combined effectively than when observed alone. The third point is the difference between the effects of the 3DCG teaching materials and the physical model teaching materials on the understanding of the topography. A quantitative textual analysis suggests that the ability to zoom in and out for the 3DCG materials and the use of the sense of touch for the physical model were useful for understanding the topography.

The objectives of this study are twofold: first, to develop a method for creating Virtual Reality (VR) teaching materials on geological formations that is not only easier to create than conventional methods, but that can also better support spatial understanding of geological formations; second, to verify the effectiveness of the created VR teaching materials. To achieve the first objective, a method for creating VR teaching materials that combines 3D models and Google Earth was developed. To achieve the second objective, a class practice for 171 second grade students in a lower secondary school was conducted, verifying the effectiveness of the new method in terms of student usability and comprehension. The usability study suggested that the use of 3D models enables users to observe the details of geological formations. The investigation of the comprehension level also revealed that the 3D model, which enables the observation of strata from various directions, can support the students’ spatial recognition of strata. The efficacy of the newly developed VR teaching material was thus confirmed.

In recent years, large-scale wind and flood disasters have continued to occur in the Japanese archipelago, and there is concern about flooding and other damage even in urban areas. Although municipalities have prepared flood hazard maps, it has been suggested that they are difficult to read. In this study, we developed a teaching material that displays urban topographic maps and flood hazard maps in 3DCG format on tablets and the Internet. Furthermore, using the developed teaching materials, we conducted a class practice for junior high school students. The results of the classroom practice showed that the use of 3D topographic maps displayed in 3DCG significantly improved the students’ accuracy rate in predicting flooding compared to that of flat topographic maps. In addition, the students’ evaluation of the teaching materials suggested that by using the 3DCG hazard map, they were able to notice the danger of inundation in depressions on a plateau, which they had not noticed on the 3D topographic map.

The spatiotemporal distribution of Cretaceous-Paleogene granitic rocks in southwestern Japan is investigated to understand the origin of the granitic batholith belt and to reconstruct the tectonic setting of emplacement. New U-Pb zircon ages for 92 samples collected from a region measuring 50km (E-W) by 200km (N-S) reveals a stepwise northward younging of granitic rocks aged between 95 and 30Ma with an age-data gap between 60 and 48Ma. Based on the spatiotemporal distribution of granite ages, we examine two plausible models to explain the pattern of magmatic activity: (i) subduction of a segmented spreading ridge and subsequent slab melting (ridge-subduction model), and (ii) subduction with a temporally variable subduction angle and corresponding spatial distribution of normal arc magmatism (subduction angle model). We optimize the model parameters to fit the observed magmatism in time and space, and compare the best-fit models. As to ridge subduction model, the best-fit solution indicates that the spreading ridge started to subduct at approximately 100Ma, and involved a 45-km-wide section of the ridge segment, a subduction obliquity of 30°, and a slow migration velocity (∼1.6cm/y) of the ridge. These values are within the ranges of velocities observed for present-day ridge subduction at the Chile trench. On the other hand, the best-fit solution of subduction angle model indicates that the subduction angle decreases stepwise from 37° at 95Ma, 32° at 87Ma, 22° at 72Ma, to 20° at 65Ma, shifting magmatic region towards the continental side. These results and comparison, together with constraints on the geometry of the tectonic setting provided by previous studies, suggest that the ridge subduction model better explains the limited duration of magmatism, although both models broadly fit the data and cannot be ruled out.

本研究では赤山地下壕跡および館山市宮城の教材化を目的とした地質調査を行い、立体的地学教材の開発を行った。赤山地下壕跡では狭い範囲で様々な方位・角度の地層断面を直接観察できる。複雑な視点移動をすることなく地層を立体的に認識できるため、地学野外観察の導入に適していると考えられる。開発した教材をもとに地学野外実践案を作成し、大学生を対象として実践をおこなった。