Comprehensive ground-motion characterization of the 6 February 2023 MW 7.8 Pazarcik earthquake in Kahramanmaras, Turkiye: insights into attenuation effects, site responses and source properties

The devastating M-W 7.8 Pazarcik earthquake on February 6, 2023, profoundly impacted a large region in south-central Turkiye and northwestern Syria, resulting in over 50,000 casualties and widespread damage. To better understand source properties and wave-propagation effects of this event, we analyze the strong ground-motion data recorded at similar to 230 stations. We determine the regional distance-dependent attenuation using the horizontal RotD50 Fourier acceleration amplitude spectrum (FAS) in the frequency range of 0.1-20 Hz. We find an apparent near-source saturation effect which needs to incorporate an additional finite-fault factor for the distance scaling. Uncertainty and sensitivity analyses are considered by variable decay rates in the geometric spreading model. For each decay rate, we derive a corresponding Q(f) model to account for the frequency-dependent anelastic attention. Significant duration of ground motions is modelled for two different measurements based on Arias intensity (I-A). For site amplification, we construct a model containing both V-S30-scaling and peak ground acceleration (PGA)-scaling. Source parameters are then determined using a reference Fourier source spectrum at 1.0 km. Specifically, we estimate the mean corner-frequency as f(0)= 0.036 Hz, Brune stress drop as Delta sigma = 4.79 MPa and the reference rock site kappa(0) = 0.051 s. By analyzing near-source pulse-like waveforms, we demonstrate that the mismatch of peak ground velocity (PGV) between our model and close-distance observations is due to the rupture directivity effect. Finally, we compare ground motions of the 2023 M-W 7.8 event to those of the 2023 M-W 7.6 Elbistan and the 2020 M-W 6.7 Sivrice earthquakes. Attenuation effects estimated for the three events are found to be identical between similar to 0.2 and 6.0 Hz, with slight differences in site responses above similar to 5.0 Hz. Source spectra comparisons indicate that the source properties are complicated for all three events. Our comprehensive ground-motion analyses contribute to understanding and modeling regional properties of attenuation, site response, and event-based source characteristics that are important for future region-specific seismic hazard assessment.