under-appreciation of risk

Not technically. Risk assessment is a very specific phrase meaning that you have identified the hazard, and then determined the probability and consequence of occurence.

An underappreaciation of risk is a fuzzier term that can mean that you have consciously minimize the appreaction of hazard probability and consequence. For instance most people have a gargantuan underappreciation of the risk of operating a motor vehicle. Else they wouldn't plug that cell phone into their ear while driving.

On the other hand, there are many tendencies to overappreciate specific risks---mostly as a consequence of emotionalism. That in my mind explains the propensity for people to trust drinking bottled versus tap water.

Rap

raprap pretty much wrapped it up in a nutshell.

systemic under-appreciation of risk. = on-going lack of awareness that the bottom might fall through.