Landslide or Fault Tip?

there were some early reports that used the fault tip movement as a measure of the slip on the fault during the 11 march 2011 Tohoku-Oki earthquake. amazing measurements made with hi res bathy data.

i saw a phenomenal 3-D view of the high resolution bathymetry in that region at the AGU meeting last week. it appears as though this previous interpretation of the fault tip may instead be a landslide. based on the 3-D view, it appears that the rupture tip was further up slope on the accretionary prism and did not extend to the trench in the latitude where the landslide is (though it did reach the trench further south, where there was less slip).

there were some submarine benchmarks that contributed to these estimates of slip, but it appears as the slip estimates that include the landslide as a measure are probably over estimates. the slip (>50 m) was large, but given the large tsunami, people accepted these interpretations. i now question these larger slip estimates with this new information. also, the landslide may be consistent with the large tsunami run ups there. we will need to see what the tsunami modelers come up with when they account for this new interpretation.

based on bathymetry and seismic reflection data offshore, Cascadia does not have these type of landslides in the recent past (in the last few 100’s of thousands of years), so probably is not at risk of these larger localized tsunamis. what was once interpreted as a landslide (the “Humboldt slide”) is not a landslide, but a series of steps formed by sedimentation and erosion.

Here is an article that discusses this from a tsunami and slip modeling perspective.

Category(s): earthquake, geology, plate tectonics, subduction, tsunami

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