LOCAL MAGNITUDE SCALE FOR MONGOLIA AND DETERMINATION OF MWP AND MS (BB)

We determined a new local magnitude (M_L) 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 M_L based on its original definition. We obtained the following formula for determining M_L 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 M_wp and M_s(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 M_L will saturate. The routine determination of M_L, M_wp and M_s(BB) is important and effective for earthquake monitoring in and around Mongolia.