By their formula 4.5 Richter implies 1.8 kt. 4.7 Richter, which I've also seen claimed, would imply 2.8 kt. They'd have to get to 5.2 Richter to equal the Pakistani's 9 kt. Trinity would have given a 5.5 had it been a "hard rock underground nuclear test," but it was above ground so their formula didn't apply.
Mb [in Richter] = 4.262+0.973 log Y [in kt]
To rewrite their formula 4.262 Richter implies 1 kt yield and yield increases exponentially by a factor of 10.66 for each 1 additional Richter point up to the yield bounds of the equation, 120 kt or 6.3 Richter.
Now I’m seeing an estimate from Japan of 5.3 Richter, which implies Hiroshima size and Russian military are claiming 20 kt yield which would imply about Richter 5.5. It generally takes awhile for the geologists to run all the data and give a final verdict on the size of quakes. I suppose we should give them at least as much time to refine their calculations as it will take to launder all the shorts in japan and Seoul, and to reboot the Teleprompter in DC.