Earthquake environmental effects and ESI 2007 of the 6th February 2023 Kahramanmaraş earthquakes along the East Anatolian Fault Zone (Türkiye)

Abstract

The February 6, 2023 Kahramanmaraş earthquake doublet resulted in a range of devasting impacts on the built and natural environments. Here the macroseimic intensity of the event is assessed using the Environmental Seismic Intensity Scale (ESI 2007), which considers a range of primary and secondary earthquake environmental effects (EEEs) resulting from the causative earthquakes. These features were documented as part of the hybrid Earthquake Engineering Field Investigation Team (EEFIT) mission and by numerous other studies in the aftermath of the earthquakes. The primary fault ruptures along segments of the East Anatolian Fault Zone exceeded 350 km along the Pazarcık segment (the first fault to rupture) with a maximum displacement (D_max) of ∼8 m, and 150 km with a D_max ∼7–8 m along the Çardak-Sürgü Fault, which subsequently ruptured later the same day in an event termed the Elbistan or Ekinözü earthquake. In addition, a range of other secondary effects such as landslides and rockfalls, liquefaction and lateral spreading, changes to springs, tsunami and widespread damage were reported over an area >35,000 km². These data indicate epicentral intensities of XI and X for the Pazarcık and Elbistan earthquakes, respectively, consistent with the intensity inferred from measured offsets along these faults. Whereas site intensities based upon various secondary effects range from VIII – XI. Given the close association in time and space of the two main shock events it is difficult to attribute the wider off-fault secondary features to either event, especially where the faults converge in the north, but there is good correlation with: a) the mapped fault traces and many documented EEEs occur with 10–15 km of the rupture; and b) measured peak ground acceleration (PGA), where ESI 2007 intensities of > X correspond to regions experiencing >0.2 g PGA, and there are a few EEEs where PGA did not exceed 0.05 g. However, both maximum reported moment magnitude intensity (MMI) and Did You Feel It (DYFI) reports are 1–3° lower than the ESI 2007 values derived here, possibly resulting from bias towards urban areas. These data not only highlight the utility of using environmental effects in earthquake intensity studies but also suggest that the Kahramanmaraş earthquakes are unprecedented within the historical record of the region.