Horizontal coordinates change modeling of Earth surface points in ITRF reference frames in the region of Iranian plateau

Being familiar with the modes of motion and coordinate changes of the Earth surface points as a function of time is very important and essential in different types of geodetic applications. The puepose of this research is the time-dependent modeling of displacement and coordinate changes of the Earth’s crust surface points due to the plate tectonic motions and earthquakes in the region of Iranian plateau. The provided model could be used to predict the coordinate changes of surface crust points or to predict the geodetic observations (distance and angle) from one arbitrary epoch to another. This model receives the coordinates in various ITRFs or WGS84 reference frames and after the computations are made, the results could be provided in any reference frame. The Bursa-Wolf seven-parameter conformal model was used to transform three dimensional Cartesian co-ordinates between WGS84 and ITRF2000. In the absence of a crustal motion, the equations for transforming positional coordinates from one ITRF to another are rather familiar to the surveying community, i.e. it is a seven-parameter transformation. In the presence of a crustal motion, the transformation equations can be generalized to allow one frame to move relative to the other. Thus, each of the seven defining parameters becomes a function of time. Therefore, in modeling, fourteen transformation parameters were used for ITRF2000 reference frame transformation to the previous and later reference frames. Okada (1985) analytical model was used to model sudden coseismic and interseismic motions due to earthquakes. In previous works (Pearson, 2010 and Meade, 2005) the block model was used for secular and interseismic deformation modeling, but in this research, we used Okada (1985) analytical modeling for this purpose since (1) Modeling the present-day velocity field determined with GPS networks incorporates geological constraints on the geometry of the main structures and on the long-term deformations; (2) Regions between the major faults are not rigid and so the modeling allows for internal deformations. Finally, we have a tectonic model for Arabia-Eurasia oblique collision zone in Iran that is more realistic than the rigid block model. This model shows that about 30% of GPS velocity field components are produced by faults inside Iran, 60% by Arabian plate and 10% by Anatolian plate. Continuous use of GPS data and local network observations is recommended to get a more precise model for secular and interseimic motions. Also using more precise geometric faulting parameters due to earthquakes obtained by inverse problem solution based on GPS or InSAR observations is recommended to get more precise outputs. Postseimic motions were not modeled in this research since this effect is a function of time and its amplitude is just considerable for large earthquakes, beside that the amount of this effect is reduced with time. Anyway, the postseismic deformation modeling due to intense earthquakes with a large focal depth using Wang (2006) model is recommended. In this research, just the effects of secular, interseismic and coseismic motions were included in the model. To complete the model, it is recommended to consider the effects of the crustal motions associated with land subsidence, volcanic activity, postglacial rebound etc.