Investigation of Palu tunnel deformations along the creeping section (hazar-palu segment) of the East Anatolian Fault, Turkey by terrestrial laser scanner

The Eastern Anatolian Fault (EAF), which forms the boundary between Anatolia and Arabian plates, is one of the most important tectonic structures in the Eastern Mediterranean region. Together with its conjugate, the North Anatolian Fault (NAF), it accommodates the westward motion of the Anatolian plate with respect to Eurasia. Although it has been associated only with small-to-moderate sized earthquakes in the instrumental period and relatively quiet compared to the North Anatolian Fault, the EAF produced devastating large (M > 7) earthquakes in the historical time. Analysis of historical seismicity suggests that a seismic gap exists between the Lake of Hazar and Bingöl, referred here as to Palu seismic gap. Recently, using GPS and InSAR, we showed that the 100km-long section of the Palu segment is exhibiting aseismic creep at the surface, in contrast to the previous studies. The creep rate varies along the fault reaching, at some places, to the far field GPS-based plate velocity (i.e., 10 ± 0.3 mm/yr), implying that significant portion of the elastic strain has been released aseismically. One of the best markers of the creeping zone is Palu railway tunnel that is 4.90m wide, 5.87m high and 787m long. It cuts by EAF and the walls of the tunnel have been offset by approximately 10-20 cm since construction in the middle of the last century. In this study, surface deformation of the tunnel has been investigated using Terrestrial Laser Scanner (TLS). The measurements have been performed using FARO Focus 3D X130 on 10.09.2018 and 19.06.2019, respectively. The first TLS data has been taken as reference for registration of the second TLS measurement. The registration accuracy has been calculated as 3.02 mm. Open source Cloud Compare software has been used to define changes between two- dataset. 2.05% of calculated distances were in 1 - 2.5 cm interval. However, in some small regions, distances varying between 2.5-5 cm have been observed. In this study, effects of calculated distances on the stabilization of the structure are discussed. This study showed that the TLS technique gives promising results for monitoring of surface deformation of Palu railway tunnel.