Analysis of information sources in references of the Wikipedia article "Optical fiber" in English language version.
Generally, fiberoptic cables, which make up most longdistance telephone lines in the United States, are more resistant to EMPs than metallic line networks. However, these wired infrastructures depend on repeaters in order to amplify the optical signal; in the case of undersea cables, this means that repeaters are placed every 60 to 70 km on the ocean floor.