20 April 2016
Images of other landslides from the Kumamoto earthquakes
Posted by Dave Petley
Images of other landslides from the Kumamoto earthquakes
In addition to the major, and well-publicised, landslides triggered by the Kumamoto earthquakes this week (which I have featured in my previous posts), there appears to be a substantial number of other major failures, many of them around the flanks of Mount Aso. There are images of these on the websites of Kokusai Kogyo and Asia Air Survey. In this post I seek to highlight some of the more interesting ones that have been photographed by Asia Air Survey.
Asia Air Survey has a very clear image of the multiple landslides that formed the flow slide that I featured yesterday. These appear to be shallow slides in (probably) an volcanic deposit. Note the cracks in the slope on the left side of the image – this will be an area to watch in the forthcoming rainy season.
Asia Air Survey also has this fascinating image of three shallow landslides:
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There is a huge amount going on in this slope in addition to the two obvious, and one less obvious (on the counter-slope) landslides. There is extensive cracking on the ridge top, and in the upper part of the image on the main slope. Asia Air Survey also has this image of a very extensive landslide system, including a large area of highly mobile debris movement:
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Note the very extensive slope cracking here as well, including a series if cracks that appear to run through the building on the ridge. I am intrigued as to whether this is a slope deformation or a tectonic crack – the position is unusual if it is the former. The largest landslide here has flowed into two different drainage systems.
Finally, and perhaps most intriguingly, Asia Air Survey have this image of a landslide system in the vicinity of what I assume is a hot spring system:
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There are signs here that the ground may have been altered (and probably weakened) by hydrothermal activity. The houses in this area will need careful assessment in light of the potential for further slope activity.
First photo shows what appears to be ridgetop spreading/shattering caused by topographic amplification. We saw similar features and many rockfalls after the 1992 Petrolia Earthquake (at the Mendocino Triple Junction in Northern California). Sackung in the region also appear to be preferentially located along ridges oriented roughly perpendicular to the seismic source here. Ridges radiating out, away from the coast and the triple junction do not appear to have such susceptibility, but I have not had time to do a quantitative study.