2:15 PM - 2:30 PM
[HCG26-03] Submarine landslides and the trigger on the Kumano Basin
Keywords:Submarine slide, Nankai trough, Mud volcano
Underwater cables are cut suddenly by submarine landslides and related bottom currents. Such a cable cut accident damages economics4). We have various observation data in the events, but we can not critically understand its trigger mechanism yet.
The trigger mechanism of submarine landsliding is thought to be earthquake shaking, pore pressure increment, slope steepening and so on5). It is possible that uplift due to mud diapir could be responsible for slope steepening. The gas-related high-pressure could induce fluid escaping from deeper sub-seafloor toward seafloor and causes mud volcanism. We observed a gas-related submarine landslide example at off-Hachinohe6). Some of the researchers challenged to understand the formation mechanisms using various soil mechanics experiments7). However, we need more descriptive and also experimental studies to understand the formation mechanism. These attempts are the first step for a prediction of the submarine landslides.
In this June, Dr. Asada (chief scientist for the cruise), Prof. Moore and others challenged to survey what at the outer ridge of the Kumano Basin using AUV Urashima during the cruise YK15-10. This challenge was a series of difficulty caused by the Kuroshio Current, but finally the Urashima recovered dataset of topographic textures, sub-bottom profiling images, side scan sonar images, and bathymetric images in a submarine landslide area, as shown by Moore and Strasser8). Based on these survey results, we conclude that
1) The submarine landslide might be critical state by a slope gradient of several degrees.
2) This slide was formed by one big slide (~1.0 x 1.0 x 0.03 km) and many small slope failures resulting turbidite layers covering on the wasted-mass.
3) This might not need any triggers for sliding (e.g. large earthquake).
4) In the wasted mass, we observed transparent dome-shaped bodies of ~several tens meters in the subbottom profiling images. These might result from fluid escaping and/or small mud volcanoes.
We further analyze in detail the Urashima’s data to decipher the trigger mechanism and also formation process of the submarine landslides on the Kumano Basin.
1) Plafker and Mayo, 1964, USGS OF-Rep., 2) Hornbach et al., 2010, Nat. Geosci., 3) Kawamura et al., 2014, Mar. Geol., 4) Hsu et al., 2008, TAO, 5) Locat and Lee, 2002, Can. Geotech. J., 6) Morita et al., 2012, Springer, 7) Sultan et al., 2004, Mar. Geol.), 8) Moore and Strasser, 2016, Springer