An expert witness at the trial over the Deepwater Horizon disaster says BP drilled its ill-fated Macondo well in an area where a magnitude 6 earthquake had struck four years before the blowout.

Andrew Hurst is a geoscience professor at the University of Aberdeen in Scotland. He was a witness for Gulf Coast residents suing BP and other companies involved in the drilling project. He testified Monday that the April 2006 quake likely weakened rock formations on the sea floor that already were more fragile than in other parts of the Gulf of Mexico.

Hurst is an expert in petroleum geology. He said he has seen evidence that BP knew about the earthquake before it started drilling the well about three years later.