GEOPHYSICAL SURVEYS FOR GROUND MODELLING OF ASHGABAT CITY

An international cooperation project between Turkmenistan and Japan regarding earthquake disaster mitigation called “The Project for Improvement of the Earthquake Monitoring System in and around the Ashgabat City in Turkmenistan” is being conducted by The Academy of Sciences of Turkmenistan and Japan International Cooperation Agency (JICA). The project has a main objective of improving capacity for earthquake observation and earthquake hazard assessment in the city. The period of the project is from July 2017 to December 2020. Within the project, both researchers from Institute of Seismology and Atmospheric Physics of the Academy of Sciences of Turkmenistan (hereinafter referred to as “the Institute”) and experts from JICA have been developing ground models to depict the seismic intensity map for the pilot areas in Ashgabat City. The Institute had already published earthquake intensity maps not only for Ashgabat City but also for the whole Turkmen territory. It has been pointed out, however, that resolution and accuracy of the earthquake intensity map of Ashgabat City should be improved to adapt to urban modernization and population growth of the city.As the first stage to improve the maps, characteristic of subsurface soils had been studied using accumulated drilling data and existing geophysical survey results. Through these studies, it was recognized that the relationship between shearwave velocity and ground condition including soil types and their properties are not sufficient to construct ground models. Therefore, geophysical surveys such as array microtremor survey, MASW (multichannel analysis of surface-waves) and PS- logging and borehole drillings with SPT have been carried out at around ten (10) locations in the city. In the meanwhile, researchers of the institute have been providing shear-wave velocity profiles at more than 1000 locations in the city by the improved HVSR (H/V spectral ratio) method. We are processing field data provided by the borehole drillings and geophysical surveys to find relationships between soil conditions and shear-wave velocities in Ashgabat city area. In addition, comparison of shear-wave velocities obtained by several different methods, namely PS-logging, array microtremor surveys, MASW and the improved HVSR method, are being studied.

کلیدواژه ها:

Ground modelling ، Shear-wave velocity ، Geophysical surveys ، Soil properties ، Ashgabat