Monday, 14 January 2013

What are we looking for?

After a few more days looking for potential sites, we thought it was probably time we gave an update on what makes a good site and what exactly we're looking for...

Ed digging a pit / pogo-sticking!

So we're working on tidal marshes which preserve evidence of previous great earthquakes. During the largest subduction earthquakes, land may suddenly subside or uplift by up to a few metres. This coseismic deformation results from extension of the upper plate during the earthquake (as in this diagram from Natural Resources Canada). The area that we are working in subsided during the 1960 earthquake. Low lying land subsided into the sea, inundating farmland and killing trees (see picture 3 of our last blog post). 

10cm of tsunami sand (light grey)
separating two different types of sediment

We have been digging pits in marshes and looking at incised banks of rivers in the hope of finding abrupt changes in sediment type which might reflect the sudden changes in the level of the land with respect to the sea. A change from a soil with lots of organic matter to a sandier, less organic sediment could reflect a change from a freshwater to a tidal flat with no vegetation. 

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