GPS velocity field and block model results in the HTJ

The GPS velocity field deduced from 2009, 2010 and 2011 campaigns for the 57 campaign sites and 14 permanent sites in the regions provides new tools to describe the deformations in the HTJ and understand the small scale tectonics. However, the campaigns are not sufficient to obtain an accurate velocity rate for some of the faults.

The velocity vectors suffer from a relative inaccuracy due to the short time span measurements (1 or 2 years). In general our campaign GPS vectors uncertainties are ~2.4 mm/yr for the sites in Syria and~1.9 mm/yr for the other sites in Turkey. This difference in uncertainties between sites in Turkey and Syria can be explained by the number of campaigns and the time span which are both greater in Turkey than in Syria. The CGPS sites in Turkey and Syria have better uncertainties with less than 1 mm/yr (Figure V.1). Some points in the Syrian side have anomalous values or direction which can be justified by the insufficient measurements (2 measurements with 1 year of time difference), (e.g., points CC01, BB02, and AA08 in Figure V.1).

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Despite the large uncertainties in our GPS results, we think that our velocity field has sufficient accuracy, especially in Turkish side, to be used for active deformation interpretation around the HTJ. If we compare the velocity vectors from our solution with those from other solutions of Reilinger et al., (2006) and Alchalbi et al., (2010) (Figures V.1 and V.2) we can conclude that in general our velocity field is in agreement with the other solution. Point AA09 from our solution attests for this agreement since it is a common point with Alchalbi et al., (2010) under other name (DOHA). The big uncertainties and the random directions of vectors are the result of the lack of measurements and not related to the measurement quality.

Figure ‎V.1: The GPS velocity field and 95% confidence ellipses representing our solution for the 2009, 2010 and 2011 measurements in the Eurasia fixed reference frame. Black arrows are from this study. Solutions from Reilinger et al., (2006) and Alchalbi et al., (2010) are plotted in red and blue, respectively.

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A block model was necessary to explain the GPS data in such a complex region from tectonic point of view. We tried to define the model which gives the best fit to the available data in the region.

Figure ‎V.2: The GPS velocity field and 95% confidence ellipses representing our solution for the 2009, 2010 and 2011 measurements in the Arabia fixed reference frame. Black arrows are from this study. Solutions from Reilinger et al., (2006) and Alchalbi et al., (2010) are plotted in red and blue, respectively. Fault mapping and slip rates from Meghraoui et al., (2011).

The model D (Figure V.3) is the model used for the interpretation of our results (as explained in chapter 4). This model is developed from the basic simple model used in the previous studies (3 plates and 3 main faults, e.g., Reilinger et al., 2006). In addition to Arabia, Anatolia, and Sinai blocks which are limited by EAF, CA, and DSF, we added an Iskenderun block bounded by the Cyprus subduction zone and the Karatas-Osmaniye fault from south and north respectively, and the Amanous block which is located at the core of the triple junction. The Amanous block was proposed to explain the SE direction of some GPS vectors in the Amanous Mountains. It is limited by Karasu fault from the east, and its limit from the

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west was proposed to be free from any elastic deformation. There is no mapped fault to the west of Amanous Mountains but we think that Amanous block exists and its western limits can be different from what we proposed in Figure V.3. With further investigations and geological studies, these limits can be defined more clearly and it can be offshore or inland fault. This fault can be connected to KOF near to Ceyhan, which explains the change from reverse-slip to dip-slip nature of the fault around the city.

Figure ‎V.3: Illustration of different blocks and relative slip rates on faults in block model D. Red arrows represent GPS-derived block velocity relative to Arabia, and black curve arrows and numbers show the directions and the values of blocks angular velocities relative to Arabia respectively.

The Block model D gives a slip rate of 3.5±0.3 mm/yr along the northern segment of the DSF. This amount of slip rate overestimates the GPS vectors in Figure V.2 where the vectors from our study and previous studies do not show any significant relative movement

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along the northern DSF between the two adjacent plates. By examining the profiles 5 and 6 in figure IV.19, we can conclude that block model fails to fit the GPS data along the DSF, while the fit between the model and the GPS measurements is better along the other faults and especially on the triple junction. This misfit between the model and measurement along the DSF can be related to the poor constraint on the Sinai plate east to the DSF, or to the unsatisfactory representing of blocks around the DSF. In such model, the DSF shows almost constant velocity rate along all its segments, where many studies suggest a clear difference in slip rate between segments in the south and the north (Gomez et al., 2007a; Le Béon et al., 2008; Alchalbi et al., 2010; Al-Tarazi et al., 2011). In order to have better assessment of slip rate along the DSF it is recommended to introduce one block or more in the model which allow for the internal deformation in the north-west of Arabia plate and the north-east of Sinai plate. The most important part of our model is the triple junction where our model has a good fit to the GPS data and allows for a good interpretation in the term of active deformation and seismic hazard.

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