Anomaly in Amazon Basin

Here’s a strange thing.  A very large anomalous grid shows up in the Amazon basin.   I downloaded an enlargeable pic I from the New Scientist, but that image is no longer available.  After a long websearch I found another that can be enlarged enough to show the Amazonian Anomaly.  I've copied here. It was at:-- http://blogs.discovermagazine.com/badastronomy/2011/03/31/the-earths-lumpy-gravity/#.Uq9lJeJtjnM  

       I suppose it could be something that went wrong in the imaging process. What do you think??