The weekly Geophysical posts converted magnitudes are based on the following:
This means the if the published value is “mb” then the formula applied is (magnitude in mb*0.7813)+1.5175 to get to approximate Mw.
If the published value is “ML” then the formula applied is (magnitude in ML*0.696)+1.7738 to get to approximate Mw.
ALL other values remain as they are and are assumed to be Mw already.
Please be aware that this is NOT always accurate and only makes an attempt to level the playing field and present all earthquake in approximately the same scale.