The obvious explanation is that a gas leak was the cause, but could it have been an explosive device?
One way to sort this out is to compare the energy content of natural gas with other types of explosions. Intuitively, one might expect that a 100 kg (220 pound) bomb would do this kind of damage. The energy content of 100 kg of TNT is 400 million joules, so how much gas would contain a similar amount of energy?
The surprising answer is that it doesn't take much, just 10 cubic meters. A typical room in a house has a volume of 30 cubic meters, of which 6 cubic meters is the oxygen that is also required to power a gas explosion. So a burst gas line in a tightly closed room would be one possible source of energy, but no one reported smelling any gas either before or after the explosion.
Credit: KOMO news
What else could it be? Suppose that a five gallon container of gasoline tipped over and spilled, then evaporated into a closed space. How much explosive power would it have? Again, the answer is surprising: 700 million joules, equivalent to a 400 pound bomb!
So, playing Sherlock, my best guess is that gasoline spilled in an enclosed space such as a well-insulated midwestern basement, which also accounts for the fact that no one smelled the distinctive aroma of a gas leak.
Having gone through this calculation, I'll have to do something about that gasoline container in our garage.