A new MD-ML relationship for Mt. Etna earthquakes (Italy)

A homogenous database of magnitude observations is a basic requirement
for seismic hazard estimation and other seismic studies. Unfortunately,
the magnitude reported in the seismic catalogue of Mt. Etna is not
homogenous. Only the duration magnitude (MD) is available up to 2005,
while since then the more stable local magnitude (ML) has also been calculated.
To have a uniform dataset, earthquake data recorded at Mt. Etna
during the period 2005-2014 were used to derive a new relationship between
local and duration magnitude, by applying the General Orthogonal
Regression (GOR), which is an alternative to least squares when the
ratio between errors on the independent and the dependent variables can
be estimated. The relationship obtained is:
ML = 1.164 (±0.011) *MD − 0.337 (±0.020)
The new relationship allows to back-extend the local magnitude dataset
to cover a period of about 15 years