11:00 AM - 11:15 AM
[HGM03-08] Magnitude–frequency distribution on the landslides induced by the 1923 Taisho Kanto Earthquake in the western part of the Kanagawa Prefecture, central Japan
★Invited Papers
Keywords:1923 Kanto Earthquake, Landslide, Sediment yield, Gutenberg–Richter law
Landslides induced by motion of large earthquakes, their aftershocks and subsequent heavy rains are an extensive hazard in the mountain regions and an unignorable phenomenon on discussing the development and denudation of the mountains and the sediment budget in long-term (e.g. Fan et al., 2019). Therefore, it is necessary to accumulate the archive of earthquake-induced landslides in the past and their characteristics in the distribution and magnitude (Wasowski et al., 2011) for disaster mitigation and understanding the landform development of the mountain and river basins.
The Taisho Kanto Earthquake occurred in 1923 triggered the numerous landslides in the mountain and hills of the southern Kanto Region, particularly the Tanzawa Mountains and Hakone Volcano (e.g. Inoue, 2013). Kanagawa Prefecture edited “Natural Disaster Map” in “1/50,000 Fundamental Land Classification Survey” in 1980s and 1990, and mapped the landslides induced by the 1923 Kanto Earthquake after it based on the results of the survey after the earthquake. Although some studies discuss the landslides induced by the 1923 Kanto Earthquake based on these maps and aerial photographs (e.g. PWRI, 1995; Suda et al., 2004; Koi et al., 2008), the digitizing and special analysis of the landslides in the whole of Tanzawa Mountains and Hakone Volcano have been limited.
Because the landslides disaster occurred in the Kanagawa Prefecture and the eastern part of the Yamanashi Prefecture by the 1703 Genroku Kanto Earthquake as well (e.g. Imamura and Kitahara, 2013), it is possible that the landslides repeatedly occurred in such as the Tanzawa Mountains induced by the earthquakes of the Sagami Trough in the past. Therefore, revealing the character of the special distribution and that on the magnitude–frequency of the landslides induced by the 1923 Kanto Earthquake might be significant datum to understand the erosion processes of the Hakone Volcano and the Tanzawa Mountains. In this study, the areas of the landslides induced by the 1923 Kanto Earthquake were manually traced and were digitized into the polygons based on georeferenced “Natural Disaster Map” described above. We report the special distribution and magnitude-frequency one on these landslides using above datum and discuss the erosion and landform development in these mountains.
It was revealed that the number of the landslides induced by the 1923 Kanto Earthquake is over 20,000, and their whole area is approximately 70 km2. The mode of the highest altitude of each landslide is around 500 m above sea level. Particularly, the landslides are densely distributed in the southern central part of the Tanzawa mountains and the somma of the Hakone Volcano, and the number of the landslides of Tanzawa Mountains is 16,000, and that of the Hakone Volcano is 3,400. The landslides area of Tanzawa and Ashigara mountains is approximately 60 km2 occupying over 80% of all landslide area. Sorted into lithology, the landslides area in pyroclastic rocks is the widest and 45 km2 occupying over 60% of all.
The area magnitude and cumulative number of all landslides induced by the Taisho Kanto Earthquake are negatively correlated according to Gutenberg–Richter (G–R) law in the area range of 103 to 106 m2. The areas and cumulative numbers of all groups of landslides sorted into lithology are correlated on G–R law. Their a-value of G–R law ranges 8 to 10, and b-value ranges 1.5 to 2. Both a- and b-value are maximum in the metamorphic rocks and are minimum in the volcanic rocks. The b-value of the metamorphic and sedimentary rocks are around 2, that of volcanic and pyroclastic rocks are 1.5 to 1.6. This probably reflects that the smaller landslides more frequently occurred in the metamorphic and sedimentary rocks area than in the volcanic and pyroclastic rocks area.
This study was supported by the Project Grant from the Co-creation Center for Disaster Resilience, IRIDeS, Tohoku University.
The Taisho Kanto Earthquake occurred in 1923 triggered the numerous landslides in the mountain and hills of the southern Kanto Region, particularly the Tanzawa Mountains and Hakone Volcano (e.g. Inoue, 2013). Kanagawa Prefecture edited “Natural Disaster Map” in “1/50,000 Fundamental Land Classification Survey” in 1980s and 1990, and mapped the landslides induced by the 1923 Kanto Earthquake after it based on the results of the survey after the earthquake. Although some studies discuss the landslides induced by the 1923 Kanto Earthquake based on these maps and aerial photographs (e.g. PWRI, 1995; Suda et al., 2004; Koi et al., 2008), the digitizing and special analysis of the landslides in the whole of Tanzawa Mountains and Hakone Volcano have been limited.
Because the landslides disaster occurred in the Kanagawa Prefecture and the eastern part of the Yamanashi Prefecture by the 1703 Genroku Kanto Earthquake as well (e.g. Imamura and Kitahara, 2013), it is possible that the landslides repeatedly occurred in such as the Tanzawa Mountains induced by the earthquakes of the Sagami Trough in the past. Therefore, revealing the character of the special distribution and that on the magnitude–frequency of the landslides induced by the 1923 Kanto Earthquake might be significant datum to understand the erosion processes of the Hakone Volcano and the Tanzawa Mountains. In this study, the areas of the landslides induced by the 1923 Kanto Earthquake were manually traced and were digitized into the polygons based on georeferenced “Natural Disaster Map” described above. We report the special distribution and magnitude-frequency one on these landslides using above datum and discuss the erosion and landform development in these mountains.
It was revealed that the number of the landslides induced by the 1923 Kanto Earthquake is over 20,000, and their whole area is approximately 70 km2. The mode of the highest altitude of each landslide is around 500 m above sea level. Particularly, the landslides are densely distributed in the southern central part of the Tanzawa mountains and the somma of the Hakone Volcano, and the number of the landslides of Tanzawa Mountains is 16,000, and that of the Hakone Volcano is 3,400. The landslides area of Tanzawa and Ashigara mountains is approximately 60 km2 occupying over 80% of all landslide area. Sorted into lithology, the landslides area in pyroclastic rocks is the widest and 45 km2 occupying over 60% of all.
The area magnitude and cumulative number of all landslides induced by the Taisho Kanto Earthquake are negatively correlated according to Gutenberg–Richter (G–R) law in the area range of 103 to 106 m2. The areas and cumulative numbers of all groups of landslides sorted into lithology are correlated on G–R law. Their a-value of G–R law ranges 8 to 10, and b-value ranges 1.5 to 2. Both a- and b-value are maximum in the metamorphic rocks and are minimum in the volcanic rocks. The b-value of the metamorphic and sedimentary rocks are around 2, that of volcanic and pyroclastic rocks are 1.5 to 1.6. This probably reflects that the smaller landslides more frequently occurred in the metamorphic and sedimentary rocks area than in the volcanic and pyroclastic rocks area.
This study was supported by the Project Grant from the Co-creation Center for Disaster Resilience, IRIDeS, Tohoku University.