First results of GPS measurements on the Ulaanbaatar geodynamic testing area

Abstract

First results of the analysis of GPS measurement data obtained from 18 sites of two local networks in the vicinity of Ulaanbaatar (Mongolia) for the period 2010–2015 have been presented. Horizontal velocity vectors are consistent with each other in the ITRF2014 system and with the velocities of the IGS permanent station ULAB. The sites move in the E–SE direction at a rate of 25–30 mm/yr, with the displacement azimuth averaging 105°. With respect to Eurasia, the vectors for most of the sites are slighly turned to the south, but they are still of SE orientation with the azimuth range of 130°–150° and magnitude values of 2–4 mm/yr. Relative horizontal velocities tend to decrease towards southeast that determines a zonal distribution of different type of relative strain patterns. The western part of the Ulaanbaatar network is characterized by the W–E oriented extension with the elongation rate ε1 = 12–16×10–8 yr–1. The shortening NW–SE trending strain with calculated value ε2 = 22.4×10–8 yr–1 characterizes the network’s eastern part. The highest values of the maximum shear strains (εmax = 10–14×10–8 yr–1) form an extended area in the center of the testing ground, which is elongated in the northeastern direction, conformably with the strike of the major geologic structures. The strain distribution pattern of the Emeelt network located within the eponymous seismogenic structures is characterized by the crustal elongation (5×10–6 yr–1) trending SE–NW and less pronounced shortening in the SW–SE directions.The axial part of the fault crossing the network in the NW direction exhibits maximum deformations.