The preliminary SKS splitting results in the central Mongolia

A passive seismic array with 60 broadband seismometers was deployed in the central Mongolia by the cooperation between Institute of Geophysics, China Earthquake Administration and Research Center of Astronomy and Geophysics, Mongolian Academy of Sciences, to carry out the deep structure observation and modeling study. The passive seismic array was distributed within the Caledonian orogen and the Hercynian orogen separated by the Ergis-central Mongolia-Eerguna fault zone. The teleseismic waveform data from part of the array with the epicentral distance of 85°—135° and M_W5.0, from August 2011 to July 2012, was selected to do SKS splitting analysis through the SplitLab package. Three methods, i.e., the minimum energy of tangential component (SC), the rotation and correlation (RC), and eigenvalue (EV), are simultaneously applied for each SKS waveform data. The preliminary anisotropy result was obtained for the central Mongolia. It shows that the time delay between fast and slow waves is within 0.8—2.0 s, and the polarization direction of fast wave is about N40°W, almost perpendicular to the geological structure strike direction of ENE--WSW. The fast direction is about 15° systematically clockwise to the absolute plate motion inferred from the HS3-NUVEL-1A model. It is also noted that not only the two different splitting modes are simultaneously observed beneath certain station, but also the fast wave direction parallel to the ENE--WSW striking direction exists beneath certain station.