We determined a new local magnitude (ML) scale for the regional
network of Research Center of Astronomy and Geophysics of Mongolian Academy of
Sciences (RCAG, MAS). We used amplitude data from the Mongolian seismic network
recorded by short-period seismographs from 143 local and regional earthquakes
that occurred during 2005–2012. The magnitude range is between 3.5 and 6.7. We derived
distance correction function for ML based on its original definition. We obtained the
following formula for determining ML
in Mongolia:
where A is the maximum amplitude (mm) observed on the horizontal component, r is the hypocentral distance (km). We found that the residuals of magnitudes determined using the above formula do not have a significant epicentral dependence. The magnitudes determined by the above formula are slightly larger (by about 0.15) than those determined by the current formula.
Since RCAG has started deployment of its broadband seismic network recently, in order to enhance its seismic monitoring capability, we determined Mwp and Ms(BB) for five local earthquakes using waveform data from a single broadband station in Mongolia. The estimated magnitudes are relatively consistent with the moment magnitudes of the Global CMT solutions, which implies that these magnitude determination methods will work well for monitoring larger earthquakes, for which ML will saturate. The routine determination of ML, Mwp and Ms(BB) is important and effective for earthquake monitoring in and around Mongolia.