06 February 2023 Kahramanmaraş (Pazarcik-Elbi̇stan) acceleration records of earthquakes spectral analysis and design acceleration comparison with spectra

In this study, strong ground motion (SGM) records were analyzed spatially and spectrally to understand and explain the shaking intensities and the causes of damage generated by the two major earthquakes that occurred on February 6, 2023, centered in Kahramanmaraş–Pazarcık (Mw=7.7) and Elbistan (Mw=7.6). In this scope, variations of peak ground accelerations (PGA) with distance and VS30 were examined, and Arias intensity, 5–95% significant duration, mean period, pseudo-elastic (PSA) and design (DSA) response spectra were calculated and evaluated from acceleration time series. It was observed that PGA values measured along the fault-rupture direction were greater than those measured at stations located perpendicular or oblique to the rupture, even at equivalent distances. No consistent relationship could be identified between the magnitudes of PGA and PSA values and the soil classes of the stations. The Arias intensity, significant duration, and mean period values indicated that the energy of the Mw=7.7 earthquake was released as high-frequency strong to very strong shaking over a short duration along the rupture surface, and as relatively lower-frequency moderate shaking over longer durations at perpendicular or oblique distances. In contrast, the energy of the Mw=7.6 earthquake was released as low-frequency shaking over longer durations along the fault zone. This situation was associated with forward-directivity effects. For both earthquakes, the PSA values calculated for stations located along the fault zones exceeded the DSA values in the plateau range (predominantly 0.15–0.4 s for Mw=7.7 and 0.05–1.0 s for Mw=7.6), in the damping region, and at high periods, even exceeding 1.0 g. Additionally, it was evaluated that during the Mw=7.7 earthquake, vertical PSA values along the fault zones reached peak levels at short periods, causing very strong vertical shaking and advanced deformations in nearby structures and soil.