Investigation of site effect in Gumushane and its surroundings with geophysical data and microzonation study

Although Gümüşhane province is a quiescent region in terms of seismicity, it carries an earthquake hazard due to its proximity to the NAFZ. In this context, since it is in a fast build process, it is of great importance to reveal the local site effects. For this purpose, multi-channel surface wave, vertical electric sounding and microtremor measurement methods (H/V, and SSR) were used. By H/V and SSR data, the predominant vibration frequency, the H/V ratio, the amplification factor and the seismic vulnerability index (Kg) values of the investigation area were determined. Moreover, earthquake hazard analysis (DHA) was carried out in the investigation area. P and S velocities, VS30 and dynamic/elastic parameters were obtained from the multi-channel surface wave data. The resistivity changes and the thicknesses of the soil layers in the investigation area were determined from the vertical electric sounding data. According to the data, the predominant vibration frequency of the investigtion area is 1.21 – 13.40 Hz for H/V and 1.56 – 13.24 Hz for SSR. However, H/V ratio is 1.12 – 9.76; the SSR amplification factor is 0.19 – 38.13, and the Kg vary between 0.094 – 22.2 for H/V and 0.18 – 314.7 for SSR. While the distribution of VS30 in this area varies in the range of 300.2 – 886.1 m/s, the soil class of investigation area is "ZC" according to TDBY (2018), "CD – C" according to NEHRP (2020), and "B soil class" according to Eurocode 8. The results of multi-channel surface wave, vertical electric sounding, H/V and SSR in the same profile were evaluated with the previous drilling data and it was concluded as "that all findings were closely related to the geological structure of the investigation area and that there was a coherence between the geological formation transitions. According to the DHA results, the probability of exceeding a 7.0 magnitude earthquake in the investigation area and its surrounding for a period of 50 years is 53.3%, and the danger level for the relative acceleration calculated according to European Seismological Commision (ESC) is determinedmedium level".