The investigation of the crustal deformations induced from the October 23, 2011 Van earthquake with geodetic techniques

In this study, co-seismic and post-seismic surface deformations due to the Mw 7.2, October 23, 2011 Van earthquake were determined with GPS measurements. In order to determine the co-seismic deformation, one week after the earthquake GPS measurements were carried out in the study area. The co-seismic displacement was estimated about 50±0.2 cm in the horizontal component. Continuously operating and other GPS stations in the study area were not sufficient to determine the post-seismic deformations, therefore a new GPS network was established on the footwall block and hanging wall block to detect these deformations associated with reverse faulting. With the GPS measurements carried out in the GPS network, the total horizontal post-seismic displacements between November 2011 and May 2015 period were determined as 33.5±0.1 cm. A two dimensional strain analysis was applied using GPS campaign measurements in order to determine the strain accumulation of the earthquake area. Considering the principal strain values (ɛmax=50.26±3.89 µstrain, ɛmin=-104.49±8.49 µstrain, γ1=-95.96±6.37 µstrain, γ2=-90.78±10.09 µstrain) obtained, it is observed that ther main strain accumulation grows through the periods accumulated and occurs close to the section of the main fault block in the footwall. Modelling the results, which were obtained using the GPS data collected after the earthquake, with the elastic displacement model, slip distributions and moment magnitudes were calculated. The slip rates are equivalent to the rates of an Mw =6.7, M0= 13.8822*1018 Nm earthquake. If post-seismic time series of GPS stations are observed, the ongoing deformation can be detected. GPS and InSAR data were modelled together and the results showed that are compatible with each other. To model post-seismic deformations that show logarithmic reduction over time with elastic dislocation model indicates that these deformations occur because of aseismic slip. The aseismic slip occurred after the earthquake has revealed that it has not only broken on the main fault but also on another fault that is stretching parallel to the main fault passing close to the city center. This study was supported by TÜBİTAK-ÇAYDAG (Environment, Climate, Earth and Marine Sciences Research Group) project number 112Y109 TUBITAK 1001. Keywords: Van earthquake, GPS, strain, displacement, afterslip, elastic modelling, InSAR