The Grand Wash basin is located in northwest Arizona adjacent to the physiographic boundary of the Colorado plateau. The area is well mapped geologically and is geophysically similar to the Basin and Range and Transition Zone in structural style and history. The occurrence of a rare swarm of earthquakes in 2016 in the basin area served as an opportunity to perform a seismotectonic analysis of the Grand Wash basin. Results of the analysis indicate the basin is presently undergoing mild east west extension. The east west extension and associated seismicity of the swarm are here suggested to be the result of stress created by negative gravitational potential energy of the Colorado plateau relative to the lower Basin and Range and Transition Zone. This is suggested by the clockwise rotation of the extensional stress at about 36° N on both the plateau and the Basin and Range and Transition zone.

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