1.  Vujić, E., M. Brkić and M. Pavasović: Recent geomagnetic investigations of Palagruža island.

Intention of this work was to examine all available recent geomagnetic survey data, in order to assess Palagruža as a potential location for a permanent variometer station. The most recent data consist of absolute, total intensity vertical gradients and Overhauser effect dIdD vector measurements, carried out in period 2008-2010. Evidences were found in low crustal field estimates, relatively low total field vertical gradient distribution over the island, quite high time series correlation with the near observatories, as well as in low noise level of geomagnetic components. These preliminary results indicate Palagruža as appropriate location for the repeat station as well as for the variometer station. However, additional investigations of the geomagnetic sea and coastal effects by using much longer time series are needed.

Keywords: geomagnetic repeat station, geomagnetic variometer station, crustal field,geomagnetic induction arrow

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2.  Rodríguez, J. A. B., J. A. P. Fernández, A. R. Vega, F. de J. L. Saucedo and K. I. C. Carreón: Magnetic susceptibility and natural gamma radioactivity as indirect proxies for characterization of sandstones and limestones of the Sabinas basin.

An analysis of magnetic susceptibility and natural gamma radioactivity is presented as indirect proxies of the characteristics of sandstones and limestones of the Sabinas basin. These rocks are located in the sedimentary sequence ranging from the Upper Jurassic to the Cretaceous. The magnetic susceptibility indicates changes in the magnetic composition of these rocks and suggests changes in their weathering degree. Ranges of values of magnetic susceptibility in sandstones and limestones allow classifying them into different groups, suggesting variability regarding conditions of origin and evolution. High values of magnetic susceptibility in limestones can be linked to sedimentation in anoxic or reducing environment, as well as with its siliciclastic content. The natural gamma radioactivity expressed in the contents of Th and relationships U/K and Th/U also suggest the degree of weathering of these rocks, mainly in the sandstones. These relations also highlight others characteristics in the sandstones related the probable provenance of sediments, its distance, degree of weathering and transport dynamics. Using the values of U/K ratio in the sandstones, it is possible to suggest the probable quartz-feldspar relationships. These ratio values classified rocks as arkose or quartzarenite, indicating the maturity of the sandstones. According to the U/K ratio values, most of these rocks which show little maturity are called arkose. Using the values of the Th/U ratio, it is possible to suggest the textures of quartzarenites, classifying them as rocks with fabric that is clast-supported or matrix-supported.

Keywords: magnetic susceptibility, natural gamma radioactivity, limestones, sandstones, Sabinas basin

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3.  Belinić, T. and S. Markušić: Empirical criteria for the accuracy of earthquake locations on the Croatian territory.

This paper presents the empirically based ground truth criteria, or shorter GT criteria, for the estimation of the epicentral location accuracy of the seismic events recorded at network stations within 400 km around the city of Zagreb. The criteria are based only on the network coverage metrics and the GT5 level represents an absolute location error lower than 5 km. They have been developed using a bootstrap resampling method: same earthquakes have been relocated many times but with different, randomly selected seismic stations. We used 330 reference events taken from the pages of ISC (ISC Reference Event Bulletin, 2008) and showed that the location accuracy is most affected by the distance to the farthest station in the seismic network, while not at all influenced by the distance to the nearest. The developed GT criteria for GT595% level of accuracy require 10 or more network stations, all within 125 km from the epicentre, and the secondary azimuthal gap (the largest gap when any given station is removed from the network) less than 200°, or the network quality metric (the deviation between the optimal uniformly distributed network and the actual network) less than 0.41. The obtained results revealed that the global criteria are too restrictive and unsuitable for the studied area since they require more regular networks. With our criteria, it is possible to achieve higher accuracy for the networks with a bigger secondary azimuthal gap or greater network quality metric. In addition, our criteria limitations are shown for the areas with simpler geological structure.

Keywords: GT criteria, epicentral location accuracy, bootstrap method, Croatia

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4.  Amiri-Bourkhani, M., M. R. Khaledian, A. Ashrafzadeh and A. Shahnazari: The temporal and spatial variations in groundwater salinity in Mazandaran Plain, Iran, during a long-term period of 26 years.

Groundwater resources are one of the main sources of water supply for agricultural sector in Iran. Therefore, this study aimed to investigate the situation of groundwater salinity in Mazandaran for use in agriculture. In this study, statistical analysis of collected data, proper semivariogram model selection, cross validation of predictions and preparing probabilistic and zoning maps using geostatistical tools in the ArcGIS software, were performed. To investigate the spatial variations and preparing zoning maps of water salinity, ordinary kriging (OK) was used and the zoning maps were prepared. Spatial structure of electrical conductivity (EC) assessment showed a moderate spatial dependence in most years. Zoning and probabilistic maps of EC showed that the salinity of groundwater will be added and the most probable salinity is related the lowland areas in the eastern part of the plain. The use of this groundwater for irrigation in the long term can decrease the rice yield and faced rice production with a serious risk. The results of the Mann-Kendall and the Sen tests indicated a decreasing trend in the area of groundwater with EC higher than one dS/m in Mazandaran plain that this expressing an improvement in the quality of groundwater in the plain.

Keywords: ArcGIS, geostatistics, rice, trend

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5.  Kowalczyk, K. and J. Rapiński: Robust network adjustment of vertical movements with GNSS data.

Long operation periods of GNSS stations give a possibility to use the data in analyzing vertical crustal movements with the accuracy better than ? 0.5 mm/y. During the analysis, the reliability must be considered. This involves the choice of the vertical crustal movements network adjustment method. In most cases, the vertical crustal movements network models are designed as absolute and related to the ellipsoid, where the movement is calculated on the basis of estimated station coordinates. The other option is choosing differential relative models, where GNSS vector coordinates are used. In this case, GNSS stations are connected and vertical movements between them are calculated. In the next stage, the network of vertical crustal movements is adjusted and the accuracy is assessed. The aim of this article is to calculate and adjust the unadjusted trend based on GNSS time series in an area located in Central Europe. The article presents the robust adjustment method with a weighting scheme. The obtained results show that the accuracy of vertical crustal movements model of 0.5 mm/y can be obtained from the GNSS observations processing. Also the benefits coming from the application of robust adjustment method are emphasized.

Keywords: vertical crustal movements in GNSS data, robust adjustment, weight in adjustment

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6.  Adetokunbo, P., O. A. Sanuade, P. Edigbue, K. Adegbola and T. Daramola: Statistical analysis of data processing in some seismic refraction methods: A synthetic data example.

The delay time method has gained attention in shallow seismic refraction survey because it has the capability to map the lateral thickness of overburden and relief of bedrock. This study addresses the comparison between the performances of the plus-minus and conventional reciprocal methods using a synthetic data. The interpretations obtained from both methods are reasonably comparable to the actual geophysical models. This suggests that either of the methods can be used to construct a geologic section. However, the result of randomized complete block design (RCBD) experiment shows a significant difference in the type of method used and this necessitate the need for further test. The pairwise comparison suggests that the plus-minus method produces a model that better mimics the actual data than the conventional reciprocal method.

Keywords: seismic refraction, plus-minus method, conventional reciprocal method, RCBD

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7.  Rožić, N.: Quality evaluation of height movement kinematic model of the Earth's crust on the Croatian territory.

The paper presents the empirical use of height movement kinematic model of Earth's crust created for territory of the Croatia, Slovenia and Bosnia and Herzegovina, in order to determine the relative height displacements of crust discrete points between different epochs. Also, presents the use of this model for the purpose of direct levelling measurement reductions determination, from surveying epoch to another unambiguously selected epoch, i.e. in purpose of height movement effects elimination from levelling network node benchmarks. For Croatian territory the quality of the kinematic model is indirectly tested, founded on the comparison of levelling measurement accuracy criteria related to the state II order levelling networks constituted with original and reduced levelling measurements. Levelling lines of two levelling networks of the II order, on the area of two deliberately selected and representative levelling loops of the Croatian state levelling network of I order, were analyzed. An accuracy criterion, using the original measurements and comparatively using the reduced measurements from their survey epoch to the I order network surveying epoch, is determined. Comparative comparison of the original and reduced measurement accuracy criteria is not clearly and unequivocally confirmed, nor completely rejected, the adequacy of the kinematic model quality for measurement reductions determination. However, comparison points to the fact that the quality of the kinematic model enables reliable determination of the relative height displacements at the centimeter level.

Keywords: kinematic model, height displacements, height movement, quality, measurement reduction, Croatia

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