SSA 2025 Annual Meeting

Surface fault rupture causes significant damage to built infrastructure, such as pipelines, making understanding its behavior important for engineering design. Engineers and geologists need to perform remote observations and field measurements of fault rupture following large earthquakes to drive this understanding. The 2023 Mw 7.8 Kahramanmaraş earthquake in south-central Türkiye provided a unique opportunity for such studies. Following the first phase of fieldwork aimed at measuring surface fault rupture near the intersection of the East Anatolian (EAF) and Narlı faults, the second phase focused on shear wave velocity measurements along and across both fault ruptures for a variety of different geologic and subsurface soil/rock conditions. We focused on one such area on the EAF where the surface fault rupture was not easily visible aerially (i.e., muted). The results of the shear wave velocity measurements in this region revealed that the surficial units of fine grained lacustrine sediment have very low shear wave velocities (< 50 m/s), leading us to hypothesize that the muted expression of surface fault rupture in this area was due to the damping effects of these weak surficial units. These soft sediments are approximately 3 to 5 m thick and likely dispersed the faulting effects broadly, leading to a lack of any concentrated surface expressions of displacement as viewed both northeast and southwest of this area. This observation has important implications for the validity of surface fault rupture models, particularly in areas with soft, low-velocity soils where fault displacement may be less visible despite significant underlying deformation.