spatial correlation

In this research, the spatial correlation between the variables representing Bouguer gravity anomaly and seismicity in Iran is evaluated. For this purpose, the gravity anomalies and seismicity data of this region have been analyzed statistically as well as geostatistically, for the period 1975-2021. Based on the findings of this study, it can be concluded that the significant correlation observed between the variables of gravity anomaly variations and the seismicity-related variables, especially the variables related to the frequency of earthquake occurrences, suggests that the gravity anomaly variations can be considered as an affective factor in seismic activity of this region.The Iranian Plateau is one of the most seismically active regions on the Earth because of its geologic and tectonic setting. This plateau is marked by high topography relief and also by great changes in gravitational and isostatic anomalies across it. Many researchers have studied the variations of gravitational anomalies across Iran, and some have pointed to the relationships between these anomalies and seismicity in this region. The Bouguer gravity anomaly is obtained by making the necessary corrections to measurements taken directly from the ground stations, and well reflects the deep density variations in the crust. This anomaly can also clearly show changes in crustal thickness in different regions, such that areas with high crustal thicknesses show negative anomalies and areas with low crustal thicknesses show positive anomalies.In this study, at first, the study region was divided into rectangles with dimensions of 0.5 by 0.5 geographical degrees and then the variables related to the seismicity and gravity anomalies were calculated and computed for each cell. Pearson correlation coefficients between these variables were computed and validated using statistical software Minitab (ver. 16.2.2). Also, maps representing the spatial distribution pattern of these variables were prepared. The remarkable similarity between the spatial patterns of variations of these variables indicates a strong correlation between the Bouguer gravity anomaly and seismicity in this region. The Pearson correlation coefficient values calculated between the variables also confirm this correlation. These values indicate that both variables of average Bouguer anomaly and the range of variations of this anomaly show a significant positive correlation with the seismicity-related variables. This degree of correlation is stronger for the variable of the Bouguer anomaly variation and moreover, this variable is more correlated with the seismicity variables associated with the frequency of earthquakes. In the next step, variograms were prepared.     The results obtained show that among the seismicity-related variables of the region, the b seismicity parameter (from the Gutenberg-Richter relation) has more spatial variability and show high spatial autocorrelation up to long distances. On the other hand, the other variables related to earthquake frequency and magnitude of earthquakes show less spatial autocorrelation. The variograms provided for the two variables representing the bouguer anomaly also show remarkable similarity to the seismicity-related diagrams. This similarity is more pronounced for the variable of the Bouguer anomaly variation. The remarkable similarities of the variograms, along with the similarities of the spatial distribution maps of these variables, may indicate a close relationship between these two series of variables. Finally, it can be concluded that gravitational forces, especially forces caused by isostatic imbalances, can play an important role in the process of earthquake occurrences in Iran.

Changes in the quality of underground resources for various reasons, especially the unconventional use of these resources can have devastating effects on the environment.In this research, groundwater quality parameters including electrical conductivity, total soluble solids, acidity, sodium adsorption ratio, hardness, bicarbonate, chloride, sulfate, calcium, magnesium, sodium, potassium, and the sum of anions and cations were used. in this research, groundwater quality data related to piezometric water wells affiliated to the Hamadan Regional Water Company for four-year periods in 2009, 2013, 2017, and 2020 in the plains of Hamadan province have been used. The results of Moran and coefficient of gery show that the spatial distribution pattern of all water quality parameters in 2009 and 2020 is random and for the parameters of electrical conductivity and sodium adsorption ratio in 1992 and 1996, respectively, with a high level of confidence of 95% and 90%, respectively, it had a spatial distribution with a cluster pattern with high values. To investigate the spatial variations of electrical conductivity using the Kriging method, water quality maps in terms of electrical conductivity parameters for the years 2009, 2013, 2017, and 2020 have been prepared. The map of electrical conductivity changes prepared from 2009 to 2020 years shows that the amount of electrical conductivity in the city of Hamedan (Qahvand) and Razan and Kaboudar Ahang plains has more increasing changes, which indicates a decrease in groundwater quality in the case study area. Therefore, planning is necessary to correct the decline in groundwater quality.

The prevailing synoptic pattern and the characteristics of the regional atmospheric circulation were studied in order to understand the predominant mechanism which governs the dry and wet spells over the southern coast of the Caspian Sea (SCCS). Monthly precipitation data from 20 weather stations located in the SCCS were analyzed for a 30-year period (1974-2003). Over this period, 10 widespread dry and 10 widespread wet months were identified for the Caspian region by investigating the spatial and temporal distributions of precipitation. Gridded precipitation data for the Middle East, provided by Asian Precipitation-Highly Resolved Observational Data Integration Towards Evaluation of the Water Resources (APHRODITE) on 0.5×0.5 degree grid along with the NCEP/NCAR reanalysis dataset on a 2.5×2.5 degree global grid were employed to determine the characteristics of the atmospheric circulation and to identify the predominant synoptic patterns during the dry and wet spells. The results indicated that the existence of a very strong ridge in the middle troposphere along with the formation of a strong anticyclone in the lower atmosphere over the northern-side of the Black Sea can be considered as the main features of the wet spells over the SCCS. The findings also indicated that the wind direction at the lower atmosphere over the Caspian Sea can be used as an appropriate criterion to separate the wet and dry spells over the SCCS so that the northerly prevailing wind during the wet spells is replaced with the southerly prevailing wind during the dry spells. Additionally, the occurrence of the dry and wet spells in the region is associated with the formation of a sea-saw pattern in vertical velocity values over the Caspian Sea. During the wet spells, formation of the descending prevailing motions over the north half of the Sea simultaneously leads to predomination of the ascending prevailing motions over the southern part. Meanwhile, during the dry spells, a reverse pattern resulting from the ascending and descending motions dominates over the Caspian region. The findings also show that it is reasonable to use the sea-level pressure changes in the Black Sea region as an appropriate index (predictor) to interpret the spatial and temporal variations of precipitation over the SCCS. In this way, during the wet spells, an increase in the sea level pressure over the Black Sea and its consequent positive feedbacks including an anticyclonic circulation over the Black Sea, northerly wind strengthening over the Caspian Sea, and air ascending over the southern part of the Caspian Sea will eventually cause an increase in precipitation over the SCCS. A reverse condition will be found in the dry spells. The investigation of the cyclones and anticyclones frequency and track during dry and wet spells indicates that the northern corridor of the Black Sea plays a very significant role in occurrence of the dry and wet spells over the SCCS. It is found that during the wet spells, the activity of the anticyclones in the northern corridor of the Black Sea is considerably increased. On the other hand, during the dry spells, a decrease in the activity of anticyclones in the north corridor is associated with a significant increase in the activity of cyclones in the region. In addition, an increase in the activity of anticyclones over the Middle East region and the Siberian high-pressure activity over the eastern-side of the Caspian Sea are taken into account as the main features of the dry spells.