The sPg
wave is one of the regional depth phases useful for focal depth determination
in the Regional Depth Phase Modeling Technique. We investigated whether sPg
phases were observed for events in Mongolia. We analyzed data from the Central
Mongolia Seismic Experiment for the 2012 Bayanbulag earthquake to investigate
whether sPg were observed. There are phases that arrived after Pg on the
observed records. The arrival time differences in the distance range between
these phases and Pg do not change much in the epicentral distance range from 55
km to 70 km, which suggests that the observed phases are sPg waves.
We calculated synthetic seismograms using the code of the reflectivity
method using a model recently obtained for South-Central Mongolia and measured
arrival time differences between sPg and Pg waves from them. A comparison of
the arrival times from the synthetic and observed seismograms in the epicentral
distance range from 55 km to 70 km suggests that the depth of the Bayanbulag earthquake
is around 10 km. It indicates that this epicentral distance range (55 km to 70
km) is good to be used to determine focal depths using the sPg-Pg pair based on
the synthetic waveforms.
Keywords: Focal
depth, Regional depth phase, sPg, Bayanbulag earthquake, Synthetic waveform.