A Practical Methodology to Estimate Site Fundamental Periods Based on the KiK-net Borehole Velocity Profiles and Its Application to Istanbul

Determination of site fundamental periods is remarkably important to classify soil deposits and to identify the resonant probability of any structures during an earthquake. Recent developments in the literature exposed that the fundamental period is a better proxy than time-averaged velocity to 30 m (V_S30 ) or the best complementary parameter to V_S30 to evaluate the soil characteristics. Because great efforts have been paid to achieve V_S30 maps of many regions and countries, an approximate methodology based on this parameter and engineering bedrock depth (Z_br ), in which the shear-wave velocity reaches 760 m/s (Z_0:76 ) or 1000 m/s (Z_1:0 ), is presented here to find out the site fundamental periods. The methodology is developed and verified using the Kiban Kyoshin network database. Outcomes of the proposed methodology are also compared with some of the literature equations and methods. The comparative studies resulted in a great correlation with a relatively low standard deviation. Therefore, it is conceivable to apply the proposed methodology easily to the regions where V_S30 and engineering bedrock depth are already known.