[S-SS10] Strong Ground Motion and Earthquake Disaster

[SSS10-03] Microtremor Array Survey at Strong Motion Stations Recording Significant Ground Motions during the 2023 Kahramanmaras Earthquake (Mw 7.8), Turkey

*Takumi Hayashida¹, Shinichiro Mori², Gulten Polat³, Nurcan Meral Ozel⁴, Koji Hada⁵, Masayuki Yamada⁵, Hiroyuki Goto⁶, Shigeto OHSATO⁷, Tatsuro Chiba⁸, Yasemin Korkusuz Ozturk⁴, Maki Koyama⁹ (1.Building Research Institute, 2.Ehime Univ., 3.Yeditepe Univ., 4.Bogazici Univ., 5.NEWJEC Inc., 6.Kyoto Univ., 7.Soil Research, 8.Asia Air Survey, 9.Gifu Univ.)

Keywords:Microtremor, 2023 Kahramanmaras Earthquake, Site amplification, Vs30

The 2023 Kahramanmaras earthquake (Mw7.8), Turkey, on February 6 (1:17 UTC) caused extensive damage in the vicinity of the fault zones, and significant ground motions were observed at strong-motion stations along the fault southwest of the epicenter. Field surveys have confirmed that the damage concentration areas do not necessarily coincide with the main fault or strong-motion observation stations (e.g., Mori et al., 2023), suggesting the importance of understanding the differences in subsurface soil structure to identify the cause of the damage. We conducted microtremor array surveys at strong-motion observation stations (13 sites) and in the surrounding areas (9 sites) in a region between Pazarcik, Kahramanmaras, and Antakya, Hatay, to clarify the characteristics of site amplification characteristics. We used McSEIS-AT (OYO Corp.) to deploy a four-point equilateral triangle array with radii (r) ranging from 0.5 to 25 m. The measurement period ranged from 3 to 20 minutes, depending on the array size. The spatial autocorrelation (SPAC) and the centerless circular array (CCA) methods were applied at each site depending on the array size (SPAC method for arrays of r ≧2 m, CCA method for arrays of r ≦2 m), and the average S-wave velocity in the upper 30 m (Vs30) was estimated from the derived SPAC and CCA coefficients and the Rayleigh wave phase velocities using the empirical relationships (Konno and Kataoka, 2000; Hayashida et al., 2023). The Vs30 values at strong-motion stations generally agreed with those published by the Turkey Disaster and Emergency Management Authority (AFAD). In Antakya, Hatay Province, Vs30 values differed between hilly and plain areas. The shallow S-wave structures obtained from this survey would provide helpful information for estimating ground amplification during the mainshock.

Acknowledgments:
This research was conducted as part of the project "Development of a new seismic intensity calculation formula based on seismic records and structural damage in the strong motion zone of the Kahramanmaras earthquake and elucidation of the intensity in the damage concentration zone based on microtremor measurements and shaking questionnaire survey (representatives: Prof. Shinichiro Mori and Prof. Nurcan Meral Ozel)" under the “J-RAPID Collaborative Research/Survey Program for Urgent Research on the 2023 Kahramanmaras, Turkey, Earthquake” by the Japan Science and Technology Agency (JST). We express our gratitude to the related organizations and residents who cooperated in the microtremor survey.