Ground-Penetrating Radar Imaging of Near-Surface Deformation along the Songino Active Fault in the Vicinity of Ulaanbaatar, Mongolia

Maksim Bano,Antoine Schlupp,Nyambayar Tsend-Ayush,Ulziibat Munkhuu

doi:10.3390/app11178242

Abstract

The seismic activity observed in the vicinity of Ulaanbaatar (UB) capital city has been increased since 2005. Several active faults have been identified in the UB area. Most of the Mongolian population is concentrated around UB (1.5 million), which is the main political and economic center of the country. Hence, the study of seismic hazard is of first importance for the country. In this paper, we present the GPR results obtained on the Songino fault which is situated at 20 km west-southwest of UB at the northeast tip of Khustai fault. The combination of the morphotectonic, GPR and paleoseismological investigations brings essential information for seismic hazards assessments. The 2D GPR profiles are measured by using 250 and 500 MHz antennae and the topography using a differential GPS. An appropriate processing of the GPR data, including the topographic migration, allows us to bring out indirect characteristics of these faults. The objective is to identify near-surface geometry and coseismic deformation along the mapped fault. The 250 MHz GPR images of the Songino fault show the evolution of the sub-surface deformation mode induced by the arched geometry of the Songino fault. We observe a clear compressive structure at its NW section, strike slip at its central section and extensive structure in its SE part.

Highlights

Despite that the seismic activity observed around Ulaanbaatar (UB), the capital of Mongolia, is relatively low compared to the activity observed in Western Mongolia (Munkhuu et al, 2010 [1]), the study of seismic hazard and the estimation of the probability of future large and potentially destructive earthquakes are of first importance for UB and the country
GPR images still show the presence of sedimentary deposits, potentially datable and affected by deformations that could be related to previous earthquakes with clear offsets of radar reflections (Figure 3)
Discussion and Conclusions ends of the fault which are associated with opposite vertical deformations

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. In the region, the geomorphology of the faults has been smoothed out due to erosion processes and a low slip rate (most likely less than 1 mm per year, Munkhuu et al, 2010 [1]); the exact location of the fault is hidden in a several meter strip In such a context, the GPR method has been proven to provide good results to characterize faults by identifying offsets of radar reflections and deformation along the strike of the fault The locations of GPR profiles discussed are indicated by blue (NW) and red (SE) arrows (modified from Tsend Ayaush, 2021 [15])

Seismo-Tectonic Environment of UB Area

GPR Investigations on Songino Fault

Result of GPR of image of the profile acquired in August

Findings

Discussion and Conclusions