The spectral decay parameter kappa in Marmara Region, Turkey

The kappa parameter (κ), which represents the ground motion characteristic in high frequencies (> 1 Hz), is modeled by the linear attenuation of acceleration spectra composed of the corner and maximum frequencies. Within this context, it was aimed to determine the high-frequency attenuation parameter (kappa) values for 161 strong ground motion stations operated by Turkey’s Disaster and Emergency Management Authority Presidential of Earthquake Department in the Marmara Region; 6648 three-component acceleration records of 1459 earthquakes were used that have occurred between the years of 1991 and 2019; the magnitudes were in the range of 2.5 ≤ ML ≤ 6.5, and the epicentral distances were less than 200 km. Signal processes were fulfilled cautiously for a fair comparison in order to calculate the kappa parameters accurately. Near-field earthquakes were bandpass filtered and windowed, and signal-to-noise ratios were regarded for per step of calculations. Kappa parameter calculation was performed according to slope evaluation between the corner and maximum frequencies in the Fourier domain for the shear wave phase of acceleration records. It was observed that the values of calculated κ0 from the station-based kappa-epicentral distance change between 0.0051–0.0748 s and 0.0074–0.0646 s for horizontal and vertical components, respectively. κ0 values obtained from the change of kappa-epicentral distance were calculated as 0.0295–0.0269 s, 0.0312–0.0303 s, 0.0427–0.0402 s, and 0.0469–0.0407 s for NEHRP site classes A, B, C, and D, respectively, and a correlation was determined between κ0 values and Vs30. For the stations whose shear wave velocities are not available, site classification was tried to be estimated according to the correlation between the same site classes. The average κ0 value for the whole region was found to be 0.0436 s and 0.0394 s for horizontal and vertical components, respectively. In addition, the relationship between kappa values and earthquake magnitude was investigated, and a linear relationship was found between κ and magnitude.