Determination of current velocity fields on Datça graben and its vicinity using GNSS measurements

Nowadays all types of positioning and navigation requirements have been met with the facilities provided by GPS/GNSS (Global Positioning System/Global Navigation Satellite System). A new era has started by active use of GNSS in geodetic and geophysical disciplines for the past three decades. Thanks to GNSS observations, high-accuracy three-dimensional static geodetic networks were established (TNFGN – Turkish National Fundamental GPS Network), under the name TUTGA in Turkish. With the technological progress, "real-time kinematic GNSS networks" have replaced static networks (TNPGN-ACTIVE, Turkish National Permanent GNSS Network-Active), under the name TUSAGA-Aktif in Turkish. Currently, millimeter accuracy level is achieved by GNSS carrier phase-based precise relative positioning method. This method of GNSS is used extensively for the determination of crustal movements. In practice, regional and local movements can be determined with the help of networks consisting of GNSS points that can represent all tectonic plates. Networks formed from TNFGN and TNPGN-ACTIVE (CORS-TR) permanent GNSS stations make an important contributions to the continuously and precise monitoring of tectonic movements and determination of deformation occurred. For the tectonic use of GNSS, a network design is made over the blocks separated by the faults and to represent the entire block. As much as the thickness of the crust in the region, enough GNSS points are established close to and far from the fault. Campaign-type or continuous observations are made at these points at regular intervals (at least a few hours or continuously). In the processing phase of the observations obtained by GNSS, global points (IGS stations) spread over the earth and whose coordinates are measured for a very long time have been used. The amount of stress and compression in the region can be estimated from the calculated displacement vectors according to the temporal changes. In this thesis study; Datça graben and its surroundings, which have been studied less than other faults and are considered to be active only in the medium term in the context of possible mobility, have been selected. The aim of the thesis is to determine the current velocity data on GNSS network points for micro geodetic purposes established in and around the Datça graben. As a result of the processing of the five-period GNSS campaigns, the displacements of the points from the time, which were first established (10/2018), to the time of the last measurements (05/2021) were determined. As a result of the processing of the data of TNFGN and TNPGN-ACTIVE stations around the selected fault zones, a new velocity field was created for the study area, and then a velocity field modelling was made for the same stations with this velocity field data. The data collected in the field were processed by the GAMIT/GLOBK software and the velocity vectors related to the mentioned points were calculated and statistical information was obtained. Among the 17 stations established in the structure of Datça horst and graben, a velocity value of approximately 35 mm/year in the SW (Southwest) direction was determined at station KD08 located within the horst structure, while a velocity value of approximately 38 mm/year in the SW (Southwest) direction was determined at station KD15 located within the graben structure. According to stable Eurasia reference frame, the rotation Euler pole solving was made. As a result, it was aimed to reveal the behavior of stations as micro-plates and visualize the interplate motion between measurement points within the micro-geodetic network. According to these results, it was observed that some of the stations located on the horst near the Kızlan fault to the North of the Datça graben exhibited similar approximately eastward movements. In addition, it was observed that the stations on both the Datça graben and the horst near the Karaköy fault to the South exhibited more complex movements. Based on these observations, the possible faults within the network were visualized.