Need an explanation for the chances in this graph

[Meerio]

In the paper Advanced LIGO they published some figures with chances. I would like to know how they know that there's a 90% chance for something to be in a specific value.

https://dcc.ligo.org/public/0122/P1500218/014/PhysRevLett.116.241102.pdf
paper here

also have some other questions:

What is a quadruple moment? (not too much terminology please)
How can you derive that from the formula, that if the chirp mass = 30 solarmasses that m1+m2 = 70 solarmasses ? (it says this in the paper with the formula for the chirp mass)
Due to what are the following noises created?

Quantum noise
Test mass thermal noise
Suspension thermal noise
Gravity gradients

 

[Orodruin]

What the paper discusses are Bayesian credible intervals. In essence, you start by assuming some non-informative prior distribution for the parameters and see how the data modifies this distribution. You then quote the smallest range of values containing 90% of the probability.