Dr. Ravindra claims that PRA works.
The only evidence he provided is that it is widely used.
That demonstrates there is a market for PRA, but not that it worksother than to provide employment (and a fig leaf).
—G.K. Chesterton
—George Box

Model event location & mag as a marked stochastic process with known parameters.
Model ground motion in a given place as a random variable, given event location and mag.
Then,
probability of a given level of ground movement in a given place is the integral (over space and magnitude) of the conditional probability of that level of movement given that there's an event of a particular magnitude in a particular place, times the probability that there's an event of a particular magnitude in that place
That events occur at random is an assumption
That ground motion resulting from an event of a given magnitude in a given place is random is an assumption
Standard argument:
underlying phenomenon is random (quantum physics)
deliberate randomization (randomized experiments, random sampling)
subjective probability
model that's supposed to describe the phenomenon (thermodynamics)
metaphor: phenomenon behaves "as if random"
"Probability" often invoked reflexively to represent uncertainty (since postwar period)
Not all uncertainty can be represented by a probability
Monte Carlo is a way to substitute computing for calculationnot for observation
doesn't reveal anything that was not already an assumption in the calculation
distribution of the output results entirely from input assumptions
randomness is an assumption, not a conclusion; distribution is an assumption, not a conclusion
Circular!
Assumes seismicity is random with known probability distribution, simulates from that distribution, and claims that simulation output validates the assumptions.
stochastic seismic models amount to saying there's an "earthquake deck"
turn over one card per period. If the card has a number, that's the size quake you get.
journals full of arguments about how many "8"s in the deck, whether the deck is fully shuffled, whether cards are replaced and reshuffled after dealing, etc.
Instead of pretending we can quantify seismic hazard, we'd be better off saying,
If we're willing to spend \$X to reduce risk, what should we spend it on?
—Karl Popper