I compared the histograms of peak value of Earthquake band RMS between lock-loss events and survived events. (plot1)
It looks difficult to define a clear threshold to distinguish them.

I fitted the histograms (IXV) with a exponential function (binned likely method). (plot2, plot3)
If we assume that the probability distribution function is  P(x) = λ^-1 * exp(-x/λ), the parameter λ is 3 (for lock-loss) and 0.06 (for survived).
So we can calicurate the value for

• P_loss / P_survive = 1     ->  x = 0.23
• P_loss / P_survive = 0.1  ->  x = 0.097
• P_loss / P_survive = 10   ->  x = 0.37

So I recomend to set the threshold as

• yellow zone : between 0.03-0.1 
• red zone : over 0.1

for eacn (IXV, EXV, EYV) seismometers' 30-100Mz band RMS (Z-axis)