{"id":28557,"date":"2018-09-06T22:28:19","date_gmt":"2018-09-06T22:28:19","guid":{"rendered":"https:\/\/blogs.agu.org\/landslideblog\/?p=28557"},"modified":"2018-09-06T22:37:56","modified_gmt":"2018-09-06T22:37:56","slug":"landslides-6th-september-2018-hokkaido-earthquake","status":"publish","type":"post","link":"https:\/\/blogs.agu.org\/landslideblog\/2018\/09\/06\/landslides-6th-september-2018-hokkaido-earthquake\/","title":{"rendered":"Landslides triggered by the 6th September 2018 Hokkaido earthquake"},"content":{"rendered":"

Landslides triggered by the 6th September 2018 Hokkaido earthquake<\/h4>\n

There is little doubt now that the major impact of the 6th September 2018 Hokkaido earthquake<\/a> is in the form of geotechnical failures.\u00a0 Whilst there is abundant evidence of liquefaction<\/a>, it is the dramatic landslides (some reports suggest about 800 individual events) that have caught the eye and, sadly, caused most of the casualties in all probability.\u00a0 The USGS Shakemap data<\/a> is providing some information about the distribution of ground shaking, although at this stage it is likely to be provisional.\u00a0 I have added to the map below the locations of the two areas of landslides that have gained most of the attention:-<\/p>\n

\"6th

USGS Shakemap<\/a> data for the 6th September 2018 Hokkaido earthquake.<\/p><\/div>\n

.<\/p>\n

The two areas of landslides shown above are dramatic.\u00a0 The ridge landslides are shown in the image below – here we seem to see failure from the ridge crest (which is typical for earthquakes) along the vast majority of the topographic feature.\u00a0 Sadly, at the toe of the slope were located a number of houses.\u00a0 The level of destruction seems to be very high; at 3 am the likelihood of escape for the occupants would have been low.\u00a0 Fortunately the integrity of at least some of the houses may have protected the occupants:-<\/p>\n

\"6th

The ridge failure landslides from the 6th September 2018 Hokkaido earthquake. Image via SCMP<\/a>.<\/p><\/div>\n

.<\/p>\n

In some cases the runout distance seems to be high.\u00a0 Note that the exposed slopes look to be both deeply weathered and wet, although there is not much evidence of water flowing.<\/p>\n

The second area shown in the maps above is the zone of extremely dense landslides shown in the image below:-<\/p>\n

\"6th

The area of intense landslides from the 6th September 2018 Hokkaido earthquake. Image via Tokyo Keizai<\/a>.<\/p><\/div>\n

.<\/p>\n

Again note that most of the landslides, which are again in deeply weathered materials, originate from the ridge crest.\u00a0 The runout distances look quite long again, and in some cases they have coalesced in the drainage lines (channels) to form larger flows.<\/p>\n

Given the earthquake magnitude (Mw=6.6 or 6.7), and depth (USGS reports 33.4 km)<\/a>, this level of landsliding is unusual.\u00a0 Indeed the USGS PAGER tool continues to indicate a low level of landslide activity<\/a>.\u00a0 It is is likely that this high level of landslides is the result of the effects of Typhoon Jebi (Typhoon 21 in Japan), which passed over Japan in the few days before the earthquake.\u00a0 This might have saturated the slopes.\u00a0 Alternative factors may include some aspect of the shaking – perhaps the frequency was exactly right to create dramatic topographic amplification in this topography.\u00a0 Or perhaps the materials – these slopes may well be formed from young volcanic deposits I suspect – were particularly susceptible to seismic shaking.\u00a0 I wonder if there might be an element of liquefaction in some of these failures?<\/p>\n

I am sure a great deal more detail will emerge in the days ahead.\u00a0 Comments and observations are very welcome.<\/p>\n","protected":false},"excerpt":{"rendered":"

More details are emerging about the landslides triggered by 6th September 2018 Hokkaido earthquake. The high landslide density may reflect recent rainfall.<\/p>\n","protected":false},"author":22,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-28557","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/28557","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/users\/22"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/comments?post=28557"}],"version-history":[{"count":0,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/28557\/revisions"}],"wp:attachment":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media?parent=28557"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/categories?post=28557"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/tags?post=28557"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}