Page "Electromagnetic pulse" Paragraph 57

According to the standard reference text on nuclear weapons effects published by the U. S. Department of Defense, " The peak electric field ( and its amplitude ) at the Earth's surface from a high-altitude burst will depend upon the explosion yield, the height of the burst, the location of the observer, and the orientation with respect to the geomagnetic field.

As a general rule, however, the field strength may be expected to be tens of kilovolts per metre over most of the area receiving the EMP radiation.