2:45 PM - 3:00 PM
[U11-05] Multi-hazard risk assessment for the Kanto region
Keywords:1923 Kanto Earthquake, 1947 Kathleen Typhoon, Multi-hazard risk assessment
The Kanto region has been hit by natural disasters such as earthquakes, volcanoes, and weather. Looking back over the last 100 years, there have been occurred several large-scale disasters such as the 1923 Kanto Earthquake and the 1947 Kathleen Typhoon. This earthquake and Typhoon have caused great damage in the lowlands from the eastern part of Saitama Prefecture to the eastern part of Tokyo. The Kanto Earthquake was an interplate earthquake that occurred in the Kanto region due to the subduction of the Philippine Sea plate. It is known that this earthquake caused extensive damage due to a large-scale fire in Tokyo. However, its seismic source could be estimated at a different location from a large fire due to the outcome of building damage. Strong ground motion occurred in a wide area from Sagami Bay to the southern part of the Boso Peninsula, which is close to the seismic source area. Strong shaking also caused damage to many houses in eastern Saitama Prefecture and eastern Tokyo, which are far from the epicenter. The Kathleen Typhoon occurred in September 1947, and although the typhoon itself passed through the Boso Peninsula, a warm front in the northern part of the typhoon was pushed up along the mountains in the western and northern parts of Kanto, bringing a large amount of precipitation. These spilled into rivers, causing the Tone River to burst in northern Saitama Prefecture, and the low-lying areas along the Nakagawa River from eastern Saitama Prefecture to eastern Tokyo suffered great damage from flooding.
All of these earthquakes and meteorological mega-natural disasters have caused great damage in the lowlands in the Kanto Region. According to the geomorphologic classification, traces of past floods such as old river channels, crescent lakes, natural levees, and back marshes are widely recognized in this lowland area. A detailed subsurface structural model developed for ground-motion simulations also show that the average S-wave velocity in the surface layer is low in this area, which greatly amplifies the ground motion. Based on natural phenomena such as earthquakes and typhoons and natural conditions such as topography and subsurface structure models, we can see the relationship between the amplification of seismic ground motions by the soft ground formed by river floods that have occurred many times in the past in this area. Furthermore, since the Kanto Earthquake and the Kathleen Typhoon occurred, the number of houses and population in this area has increased significantly. It is conceivable that the scale of disasters in the event of similar earthquakes and precipitation occurring in the future will become even larger.
Especially in areas that are inevitably affected by these different types of natural disasters, it is necessary to consider what kind of natural disasters will occur in the future and what kind of countermeasures will be necessary. It is effective to compare a wide variety of natural disasters in terms of the degree of impact and urgency, and to be able to get a bird's-eye view of possible natural disasters. Therefore, it is necessary to advance the sophistication of simulation technology related to natural disasters for impact assessment. In addition, it is important to collect observations and damage data of natural disasters and to link them with geospatial information in order to make a visible catalog for urgency assessment. Based on this catalog, it is possible to move forward to estimate the possibility of the occurrence of future disasters. In this presentation, we will report on our approach to probabilistic multi-hazard risk assessment for natural disasters such as earthquakes, volcanoes, and weather.
This study is conducted as a part of the research project “Research on the hazard and risk assessment” at NIED.
All of these earthquakes and meteorological mega-natural disasters have caused great damage in the lowlands in the Kanto Region. According to the geomorphologic classification, traces of past floods such as old river channels, crescent lakes, natural levees, and back marshes are widely recognized in this lowland area. A detailed subsurface structural model developed for ground-motion simulations also show that the average S-wave velocity in the surface layer is low in this area, which greatly amplifies the ground motion. Based on natural phenomena such as earthquakes and typhoons and natural conditions such as topography and subsurface structure models, we can see the relationship between the amplification of seismic ground motions by the soft ground formed by river floods that have occurred many times in the past in this area. Furthermore, since the Kanto Earthquake and the Kathleen Typhoon occurred, the number of houses and population in this area has increased significantly. It is conceivable that the scale of disasters in the event of similar earthquakes and precipitation occurring in the future will become even larger.
Especially in areas that are inevitably affected by these different types of natural disasters, it is necessary to consider what kind of natural disasters will occur in the future and what kind of countermeasures will be necessary. It is effective to compare a wide variety of natural disasters in terms of the degree of impact and urgency, and to be able to get a bird's-eye view of possible natural disasters. Therefore, it is necessary to advance the sophistication of simulation technology related to natural disasters for impact assessment. In addition, it is important to collect observations and damage data of natural disasters and to link them with geospatial information in order to make a visible catalog for urgency assessment. Based on this catalog, it is possible to move forward to estimate the possibility of the occurrence of future disasters. In this presentation, we will report on our approach to probabilistic multi-hazard risk assessment for natural disasters such as earthquakes, volcanoes, and weather.
This study is conducted as a part of the research project “Research on the hazard and risk assessment” at NIED.