Analysis of near-fault ground motions in the February 2023 Kahramanmaras, Türkiye, earthquake sequence

The southern Türkiye and northern Syria areas were hit on February 2023 by a large earthquake with M_w = 7.8, followed by another large aftershock with M_w = 7.5. The two-earthquake sequence, coupled with a series of smaller aftershocks, caused severe structural and geotechnical damage and fatalities. The objective of this study is to investigate the characteristics of near-fault ground motions observed in the earthquake sequence. To this end, the ground motion intensity measures are firstly compared with existing models; it is shown that PGA and spectral accelerations from both the non-pulse-like and the pulse-like motions are overall captured by the Zhao et al. (Bull Seismol Soc Am 96(3):898–913, 2006, https://doi.org/10.1785/0120050122) model. Subsequently, the velocity pulses in near-fault ground motions are not only quantitatively identified, but are also parameterized using the progressive iterative approach. The identified pulses are then empirically categorized into two groups of records with different causative effects according to the criterion of whether or not non-zero displacements could be visually inspected at the end of the integrated pulse displacement traces. Pulse-like ground motions containing baseline offset are also corrected, and final permanent displacements due to fling-step effects are accordingly derived. To determine the orientations at which the strongest pulses can be observed, two different approaches are employed. It is revealed that the indirect method by seeking the orientation of the maximum PGV appears to be not reliable if it is to find the strongest pulse, at least with respect to the 2023 Türkiye earthquake sequence.