What would cause it?
There are cosmic events that could cause an Electromagnetic Pulse but the most likely cause of an EMP is via a nuclear weapon explosion. The detonation needs to occur within your line of sight or above your horizon for it to effect you. It is possible that a powerful enough detonation far above the United States could impact the entire continental United States.
Equipment can generate small, focused EMPs. This sort of equipment is impractical to deploy as a weapon. EMP bombs are possible but they are an order of magnitude less powerful and impractical compared to a nuclear EMP effect. They could be an option to avoid the political fallout an organization would attract by using a nuclear weapon.
Rogue states like Iran and DPRK are not capable of a continent-wide EMP attack on the United States. They could effect a metropolitan area with a detonation at the site or they could effect coastal cities by launching a nuclear weapon a modest distance into the air and then detonating.
What would it be like?
The effects of an EMP blast are not an absolute by any measurable axis. The effect on electronics will be spotty with the highest rate of effect in the nearest area. Electronics generally thought to be immune may fail (electronics with some shielding, even vacuum tubes). More solid state electronics that aren’t properly shielded may fail at a higher degree. To put it simply, some or all of your electronics may not work.
Most cars should not be effected by an EMP. Cars are basically a big Faraday cage and will shield most of the electronics. Broad, spotty effects on infrastructure would happen. ATM machines may not work, communication may be disrupted. The power grid might face problems.
What could you do?
Protecting your own equipment
Prevention means encasing equipment you care about in a Faraday cage or getting hardened equipment in the first place. Sometimes this means that the equipment has its own integrated Faraday cage.
A Faraday cage can be improvised. It’s simply a metal box covering your equipment completely, there is no need for it to be air tight. There is no need to ground the metal box. Your electronics must not touch the metal of the box. Think an ammo can with any sort of insulation material (wood, paper wadding) and inside of that is your hand-crank radio.
Before you surround all your electronics with a Faraday cage you need to consider how useful the equipment will be if a large scale EMP happened. Would Internet infrastructure be damaged such that it doesn’t matter that your wireless router is shot? Would cable services be cut such that it doesn’t matter that your DVR is inoperable? For that matter what if the overall power grid is unable to survive an EMP, all your electronic devices are useless anyways.
If you’re inclined to think an EMP could happen then my example is probably the most reasoned prevention; preserving a hand-crank emergency radio, maybe place a small laptop inside of ammo can as well.
Societal impact
More important than damaging your electronics is the prospect of major disruption for society. All general preparation applies. Just-in-time food delivery, communication, law and order may all be disrupted.
- Have some money on hand in case the bank cannot access account information.
- Have food and water for at least 72-hours and ideally 2 weeks.
- Make whatever preparations you think necessary for civil unrest.
