Theory-

In the western U.S. you can use DEW for underground warfare, looks just like earthquakes.

But east of the Mississippi, you can't have 40 or 50 quakes a day, even small ones, without panic.

So you burn the tunnels out. With wildfires as a cover.

Smells like plastic and rubber and chemicals burning, because that's what it is. Server farms and power systems and entire underground cities.