مجله ژئوفیزیک ایران
سال هفدهم شماره 1 (پیاپی 58، بهار 1402)

In probability theory and statistics, Bayes' theorem , describes the probability of an event, based on prior knowledge of conditions that might be related to the event. One of the many applications of the theorem is Bayesian inference, a particular approach to statistical inference. When applied, the probabilities involved in the theorem may have different probability interpretations. With Bayesian probability interpretation, the theorem expresses how a degree of belief, expressed as a probability, should rationally change to account for the availability of related evidence. Bayesian inference is fundamental to Bayesian statistics. The purpose of this study is a modeling method based on hierarchical structure in prioritizing and providing appropriate solutions to reduce seismic hazards in the Alborz-Azerbaijan province. The basis of the work is based on using natural data and Bayesian statistics which is a powerful tool in modeling both uncertainty and randomness. The method can correctly show the values of peak ground acceleration (PGA) along with the quantities of its distribution function in the region. The input information for the method is seismic catalog from 1900 to 2020 and proper ground motion attenuation law. It should be noted that Iran strong motion network had limited data so that there was a gap of large earthquakes of data. This modeling contains a set of processes and rules for using and specifying variables and relationships between them. Based on the results of this study, conducted in the northern and north-western parts of Iran, using Iranian Seismological Center data (http://irsc.ut.ac.ir) that includes 11 stations in the study area, hazard maps were drawn for PGA over a period of next 50 and 475 years, with the highest acceleration in the Alborz region including Tehran and Zanjan and in the Azerbaijan region including Tabriz and Rasht. The correlation between estimated acceleration values by Bayesian method and the values observed by the accelerometer network of Iran Road, Housing and Urban Development Research Center was α=0.95. This indicates that the estimated maximum acceleration is in a good agreement with the observed maximum acceleration. According to the results, the southern part of Alborz (Tehran) and the north-western part of Iran (Tabriz) had the highest PGA. Then, the Bayesian method will give favorable results for probability seismic hazard analysis.The results confirm the uncertainty of different parameters of seismic acceleration. Therefore, all of these parameters calculated, indicate that in the west of the Caspian Sea (Rasht city) the lowest value was allocated. Then, Bayesian method with advantages such as considering the relationship between variables, conditions of uncertainty and high flexibility, has the necessary ability to analyze seismic risk in other parts of Iran. This method can also be used in construction projects. In carrying out such renovations, it is necessary to provide step-by-step protocols and rules guidance for application and specification of variables and relationships between them in designing and correcting the model.

In recent years, due to the large earthquakes occurred near important and residential areas of the world and the great financial and human losses left, researchers have investigated the effects of different near fault field earthquakes from earthquakes far from the faults.    Near fault field earthquakes have different nature and unique characteristics that may increase the severity of damages and not considering this phenomenon, can increase the damages several times. Therefore, one of the most important and new issues in the seismic design of buildings, bridges, structures with wide spatial distribution and vital arteries, is to pay attention to the vertical component of the earthquakes.Field observations show that many of the damages at short focal lengths, especially in the vertical members of long spans of bridges and buildings, are due to the strong motion of the vertical component.This study has been conducted to consider the effects of the vertical component and the ratio of vertical to horizontal components of near fault earthquakes in Iran due to the importance of the issue and also due to the lack of extensive research in this field according to the Iranian data. In this research, 450 records of near fault field in Iran have been prepared from the Housing and Urban Development Research Center of Iran. Then, 75 records which had pulses with forward directivity, and also their horizontal components had a pulse (perpendicular to the rupture direction) were determined. Using the acceleration response spectrum of these components, the spectral ratio of the vertical component to the horizontal component is determined.The aim of this study is to determine the V/H spectral ratio based on the Iranian database and to provide the relevant relationships for the two categories of rock and soil. Due to the small number of recorded data from earthquakes near the fault and also for considering the local effects of the site, the recorded data on type 1 and 2 (VS ≥ 375 m/s) soils are used as rocky sites and type 3 and 4 (VS ≤ 375 m/s) soils are used as soil sites. Although the acceleration response spectrum of the vertical component of an earthquake is proportional to the acceleration response spectrum of its horizontal component, this ratio is not a fixed number and depends on the various parameters such as period, distance from the fault, soil type, earthquake magnitude and fault mechanism.  According to the results, determining the value of 0.67 for the V/H ratio for two categories in the range of 0-4 seconds is not conservative and it is a small value. Based on the seismic data of Iran, this coefficient in two categories of rock and soil is equal to a value of about 0.8. Therefore, it is recommended to use the V/H spectral ratio proposed in this research in the regulation 2800 (which considers the effects of the vertical component of the earthquake for some structural members), as well as in structures with network distribution and lifelines.

Global warming is a gradual increase in the Earth's temperature generally due to the greenhouse effect caused by increased levels of carbon dioxide. Global warming has had significant consequences for human life, significantly affecting agricultural production, ecosystems, and water resources. The climate system of the Earth responds to a perturbation to the top of the atmosphere radiative balance through a change in temperature. This imbalance constitutes a radiative forcing of the climate system, and the magnitude of the response is determined by the strength of the forcing and the net radiative feedback. Equilibrium Climate Sensitivity (ECS) is an estimate of the eventual steady-state global warming at double CO2 and Transient Climate Response (TCR) is the mean global warming predicted to occur around the time of doubling CO2 in GCM and ESM runs for which atmospheric CO2 concentration is prescribed to increase at 1% per year.   This study aimed to evaluate the performance of Climate Model Intercomparison Project Phase 6 (CMIP6) models by selecting 30 models considering TCR and ECS and to investigate temperature spatial distribution and annual trends in Iran. The performance of these models has been investigated with data from Iran’s fifty-one synoptic stations for the historical period (1980-2014) using the Taylor diagram and box plot. The results showed that most CMIP6 models have good performance in simulating spatial temperature patterns. However, in the area-averaged, 73% of the selected models have estimated the temperature of the country as less than the station data. In general, more than 56% of the models showed a correlation higher than 0.5 compared to station data in the area-averaged temperature of Iran. Four models including CanESM5, INM-CM5-0, TaiESM1, and UKESM1-0-LL have shown the highest performance in estimating the temperature in Iran. The area-averaged annual temperature trend, which was examined by the modified Mann-Kendall test, showed that the temperature trend of CMIP6 models is increasing along with the observational data for all models. Most CMIP6 models, however, have simulated higher warming rates in the historical period, which differs from station data. These differences cannot be explained by internal climate variability (ICV), and the equilibrium climate sensitivity of most CMIP6 models has created a greater rate of warming in the models. For example, models such as CanESM5 and UKESM1-0-LL, which showed the highest trend, had the highest ECS and TCR among all.

Studies show that celestial bodies can be effective in triggering earthquakes from several perspectives by exerting gravitational forces, albeit less than cumulative tectonic forces. These forces in the fluid environment increase the pore pressure and facilitate the rupture and seismicity of the earthquake. Previously, no clear relationship between tidal forces and seismic events with strike-slip faults has been reported.-In this study, the relationship between earthquakes and tidal stress components in the fault area along the sinistral strike-slip of Mosha was investigated. For this purpose, IIEES and NEIC seismic data from 1975 to 2020 have been used.After removing the foreshocks and aftershocks by the Reasenberg method and considering the magnitude of completeness (Mc=2.8), 84 seismic events out of 188, with a magnitude of more than 2 around the fault were studied. -By considering the superficial fault information and the hypocenter of the earthquakes and assuming that the events occurred on the fault plane, the mathematical equation of the fault plane is fitted and modeled.According to the model of the presented fault segments, the main and shear stress components were included and calculated in the frame with the help of the conversion matrix. The results show that the north-south horizontal component of tidal stress has the greatest effect on tectonic forces and facilitates seismic shock. Based on the model of fault segments, the main tidal stress components (two horizontal components and one vertical component) and shear stress are framed into the modeled plane. Events are examined in the frame of modeled planes by Schuster’s test and binomial method, in two conventional modes of 360 and ±180 degrees of tidal phases. -Outcomes of these results are a bit complex. However, the results of the Schuster’s test at the test level of 5% (significance level 95%) do not show the correlation between tidal forces and earthquakes in the general case (in magnitude range 2.8-4.9) and we could not assume a relation between earthquakes and tidal forces, but using the classified magnitudes confirms this relation at specific intervals for different tidal components. For example, the components of tidal shear stress framed in the fault plane (parallel to the rupture of the fault main plane) are associated with a magnitude range of 3-3.9. The binomial test also does not rule out seismic events in some phase cases, where we expect the greatest effect of tidal stress on the dynamic sections of the phase. The study of tidal components shows that the negative values of the north-south horizontal component (towards south) play an important role to decrease the minimum tectonic stress at the beginning of the rupture, which is northward and as a result, the Mohr envelope failure tends to shift to the left. It facilitates fault plane rupture and can cause earthquake triggering.

During the last two decades, the south part of seismotectonic zone of Zagros (Fars) was active. The Zagros seismotectonic belt consists of a series of fault-related folds that within their evolution, seismic areas and hydrocarbon reservoirs formed. Although the characteristics of Zagros are well known, the distribution of active deformations, style of fault-related folds, and its seismotectonic behavior are among the features that require further investigation.    In this study, changes in seismic rate based on changes in seismic parameter (b-value) and fractal dimension of seismicity (D-value) have been investigated using instrumental seismic data in the period of 2000 to 2021. Total amount of b-value and D-value were calculated by the least square’s method and the correlation integral method, respectively. The map of these parameters was plotted by interpolation method.    Frequency-magnitude distribution power law (logN=a–bM) relates the cumulative number of earthquakes (N) to their magnitude (M). This ratio is frequently used in seismic studies. In this relationship, a-value describes the productivity and b-value characterizes relative size distribution of earthquakes. Most b-value studies associate the seismicity parameter with the physical properties of a particular zone.    Since the introduction of fractal in 1976, the fractal concept has covered a wide range of pure mathematics and many experimental aspects of engineering. It has found a comprehensive concept. We analyzed seismicity using the IIEES and IRSC catalog. Decreasing the b-value in the northeastern of study area indicates that stress is increasing, which may signal a future sizable earthquake. The spatial variation of b-value suggests that the SW segment is less stressed compared to the NE segment.Considering that the correlation coefficient is about -0.78, the probability of occurrence of large earthquakes on large area faults increases. The zoning map parameter b-value to D-value ratio found valuable information on the invariance property of the seismic variation scale in the area. These results suggest that this approach can be used as a useful tool to evaluate seismic power distribution on active seismotectonic regions.    According to the zoning maps and the identification of high stress zone in the study area, the north parts of MFF, around Jam and Farashband and in the later stages, Khormuj will be the main candidate areas for future earthquakes. The seismicity pattern analyzed does hold the key to understand the seismotectonics of the region.

PmP and SmS are secondary phases that are reflected from Moho discontinuity. Moho reflected phases contain information from the entire crust, thus their travel time and waveforms contain significant information about crustal structure. We used seismogram data associated to earthquakes with magnitude larger than 3.0 and focal depth shallower than 35 km occurred during 1996-2017 in NW Iran. The seismographs of each earthquake are investigated separately. After removing mean and trend, we examined appropriate band pass filters. In this study, the response of sensor in our interest frequency (1-10HZ) is similar; thus, we did not remove instrument response.   Particle motion of PmP reflected phase is similar to P direct phase as compressional waves and particle motion of SmS and S phases show that these phases get to stations as shear waves. If the travel time difference of picked Moho reflected and direct phases is less than 0.75 sec, picked reflected phase is reliable. We found that Butterworth band pass filter with corner frequencies of 0.5 and 4 HZ is appropriate for providing clear PmP reflected phases and the corner frequencies of 0.2 and 4 HZ are appropriate for SmS reflected phases. In general, the amplitude of the reflection phase could be shorter than the direct one due to large attenuation along the long ray path and missing some energy at the reflection boundary, but in some samples, amplitude of Moho reflected phase is larger than the direct phase, due to increment of Q values in lower crust with respect to upper crust and source of the earthquake. In this research, we often investigated the cases that amplitude of the reflection phases is larger than direct ones. We picked P and PmP from vertical component and considered the transverse and radial components for picking SmS reflected phase. S phase is read from the component where the SmS phase is more clear and noticeable. However, we can read S phase from each of the two horizontal components but in general, to avoid each time delays likely generated by anisotropy, it was read from the identical components used for picking SmS phase. Consistent with our research, the slope of the curve of difference between reflected and direct phases increases with focal depth and epicenteral distance, but for focal depth greater than Conrad discontinuity and epicenteral distance more than 80 km, the rate of increment of slope increases. Regarding this, a total of 216 PmP, 310 first P, 254 S and 161 SmS phases were picked from seismograms in the local earthquakes of NW Iran.

Skill assessment of global weather forecasting systems in different regions and time scales can not only improve the performance of the models based on the use of appropriate parameters for modeling or methods for post-processing, but also increase our understanding about performance of forecasting models in regions and different time scales. Accurate precipitation forecasts can play an important role in water resources management as well as reduce damages caused by heavy rainfall.    In this study, we assess the use of the Weather Research and Forecasting (WRF) model to downscale NCEP Climate Forecast System Version 2 (CFSv2) atmospheric reanalysis for generating a monthly precipitation forecast over Iran. The WRF model is configured with two-way nested domains of 60-20 km horizontal resolution. It is used to produce precipitation forecasts based on four different configurations and six initial conditions of CFSv.2 data (totally 24 members) for October-April precipitation over the period 2000-2019 (as hindcast). Performance of ensemble members was evaluated according to the Kling-Gupta-Efficiency (KGE) in comparison with 145 meteorological stations over Iran. Each member has a rating of 1 to 24. The weighted average method was used to calculate the average precipitation obtained from 24 members. To evaluate the performance of WRF-CFSv.2 ensemble model in monthly precipitation forecast, we used some criteria such as False Alarms Rate (FAR), Proportion Correct (PC), and Heidke Skill Score (HSS) for the verification of categorical forecast and Root Mean Square Error (RMSE), Nash-Sutcliffe Efficiency (NSE), Pearson Correlation Coefficient (PCC) and Mean Bias Error (MBE). The results showed that the average values of NSE, RMSE, MBE and PCC of ensemble model for hindcast were 0.46, 365, -5.7 and 0.67, respectively. Categorical indices indicated that the model skill in forecast of each precipitation class (below normal- less than 33rd percentile, normal- between 33rd and 66rd percentiles, above normal- greater than 66rd percentile) has an accuracy of 52%. Evaluation of the efficiency of the model for a test period (October-April precipitation over the period 2019-2020) shows that the model is able to forecast the distribution of monthly precipitation over Iran. In this case study, the results show that the forecasted monthly precipitation has a positive correlation (PCC = 0.68) with the observations. The results suggest that the WRF-CFSv.2 ensemble forecast based on 24 members can be useful for flood forecasting and water resources management, although the amount of precipitation forecast has bias in some precipitation systems.

In this study, coda wave decay parameter, coda Q, is evaluated using waveform data of three networks in the east and northeast of Iran based on the single-scattering method. The database includes 300 earthquakes with magnitudes in the range of 2.5-6.0 recorded in 2012 to 2020. The waveforms were gathered from the Iranain Seismological Center (IRSC) of the University of Tehran, National center of Broadband Seismic Network of Iran (BIN) at the International Institute of Earthquake Engineering and Seismology (IIEES) and Seismological Earthquake Research Center of the Ferdowsi University of Mashhad (FUMSN). The coda Q for the east-northeast of Iran was calculated as Qc = 125f 0.76 for a lapse time of 40s and optimal parameters of our database. We also evaluated coda Q based on parameters proposed by Havskov et al. (2016) as Qc = 90f 0.87 and as can be seen, the difference in the parameters leads to the different results. Furthermore, the effect of different parameters in estimating the quality factor of coda waves was investigated. The frequency dependence of the wave attenuation coefficient is evident in this region. Considering the 10-year interval of earthquakes used in the east and northeast of of Iran in this study, the obtained results indicate high seismicity rate and continuous seismic activity in the study area.   Recently some studies have been conducted to study the seismic wave propagation effects in this region. For example, Safari et al. (2020) investigated the attenuation of seismic waves in the Fariman region based on 122 local earthquakes recorded in a temporary dense seismic network of IIEES. Based on this research, the frequency relationship Qc = 66f 0.84 for a lapse time of 20s was obtained.The results of the quality factor studies depend on tectonic regime of the study area and various proccesing factors, such as: the lapse time, filter bandwidth, the window length, etc. Therefore, accurate comparison is only possible when similar parameters are considered in different studies.    We compared our results with several studies in different regions of  Iran and other parts of the world. The estimated values of Q0 in this area are in the same range of active regions of the world (Q0 <200) and is near to the results of studies conducted for another active regions of Iran. The results of our study are in good agreement with previous studies and indicate the strong frequency dependency in attenuation of seismic waves in northeast of Iran Plateaue. The observed small differences in coda Q estimates originate from differnet tectonic rigions and  processing parameters.

Due to its special geographical location, Iran has a high potential for the use of renewable energy. At present, electricity in Golestan province is supplied from Neka and Aliabad Katoul power plants, which due to the increase in population, it is necessary to build new power plants. In this study, the annual and monthly solar energy atlas maps were prepared using solar radiation data recorded in meteorological stations, GEOS-5, and ERA5 data to help decision-makers to locate suitable places for the establishment of solar power plants in different parts of Golestan province. In recent years, along with other kinds of data, the use of reanalysis data of numerical forecasting models has become popular, especially for those areas which are not covered by satellites and also to fill data gaps. To reach the goal of this study, statistical gaps in meteorological station data in the selected period (from 2014 to 2020) have been filled using the ratio method; then RUN-TEST method has been used to test the homogeneity of the data. To check the accuracy of data, the Absolute Error (MAE), Mean Bias Error (MBE), Mean Square Error (RMSE), and Coefficient of Determination (R2) between actual radiation values and GEOS-5 data as well as ERA5 data were calculated. The results show that although the accuracy varies across different locations and periods in the province, in general both outputs are suitable for estimating solar radiation and the correlation coefficients in both methods are significant at 95% confidence level. Annual solar radiation zoning of Golestan province indicates the range of annual radiation varies from 1089 kW/m2/year in forested mountainous areas up to 1800 kW/m2/year in the southwestern heights where the average of total annual radiation is 1485 kW/m2/year. The region of maximum annual radiation is located in the southwestern heights of Golestan province. In this area, solar rays strike the ground more vertically than in the other parts of the province, and also it has a semi-arid and cold mountainous climate. Moreover, the northeastern region of Golestan province has suitable annual solar radiation (1500 to 1600 kW/m2) due to its semi-arid climate and the high annual sunshine hours. The overlap map of the received radiation of Golestan province with its topography shows the appropriate quality of zoning in this area. The results of this overlap map indicate that the annual solar radiation is minimum in forested and wet areas and is maximum in semi-arid and low rainfall areas of the province. Therefore, the northeastern and southwestern regions of Golestan province have a good potential for utilizing solar energy.

In this study, the distribution of tropospheric ozone as an air pollutant and an important greenhouse gas has been investigated in various layers of the troposphere over Southwest Asia. This research has been conducted for a 5-year period (2012-2016) using the Copernicus Atmosphere Monitoring Service Reanalysis (CAMSRA) dataset, the result of the third European Centre for Medium-Range Weather Forecasts (ECMWF) project on atmospheric composition reanalysis. The analysis of the monthly mean concentration of tropospheric ozone over Southwest Asia and its time series (6-hourly data for the 5-year period) over three areas in northwestern and southeastern Iran, and Tehran show that the concentration of ozone has an annual cycle, with the maximum in summer. The maximum ozone in different layers of the troposphere (at the surface, and 700 and 500 hPa) occurs during summer. The maximum concentration in the lower layers (up to 700 hPa) is mostly caused by anthropogenic sources, while in the middle to upper troposphere, it is the result of the injection of stratospheric air into the troposphere. The high concentration of NO2 in highly populated metropolitan areas, such as Tehran and industrial areas in the Persian Gulf and the Gulf of Oman, contributes to the photochemical production of ozone. In these areas, the concentration of ozone is higher during the daytime and summer compared to the nighttime and winter. This is due to the increase in the photochemical production of ozone when the incoming solar radiation is high. Moreover, there are two hot spots of ozone concentration at 500 hPa over two regions: the eastern Mediterranean region and the east of the Caspian Sea toward Afghanistan. Large-scale subsidence and the occurrence of the tropopause fold and/or the stratosphere to troposphere transport (STT) in these two regions, linked to the Indian summer monsoon, are the main causes of the occurrence of high concentrations of ozone in the middle troposphere. The monsoon diabatic heating can induce Gill-type Rossby waves that propagate westward and cause descent via the interaction with the midlatitude westerlies. The topography of the region, e.g., the Zagros Mountains, is also effective in increasing this descent. In general, every horizontal airflow that encounters steep isentropic slopes at the upper and middle troposphere is forced to descend. We were able to detect a wave-like pattern in ozone concentration at the 300 hPa level, which can be linked to a corresponding pattern of vertical velocities in the region. Furthermore, the statistical analysis indicates that high ozone concentration events frequently occur in southeastern Iran. This could be due to transient variations in the monsoon circulation over India, the Tibetan anticyclone, and the mid-level anticyclone, all of which also affect the transport of the stratospheric ozone in the region.

Geoid determination using Stokes’ integral requires that all masses above geoid (topography + atmosphere) to be removed. Using 2nd Helmert condensation model, the topographical masses were replaced by a surface layer on the geoid. This replacement caused changes in gravity and equipotential surfaces which are so-called direct topographical effect (DTE) and indirect topographical effect (ITE), respectively. There are two different methods to formulate the Helmert topographical effects: Moritz-Pellinen and Vanicek-Martinec methods. In the Moritz-Pellinen method, the DTE is defined as the gradient difference of topographic potential of topography at the terrain and the potential of the condensation layer at the geoid surface, while in Vanicek-Martinec method both real and condensation potential refer to terrain surface. In study of Jekeli and Serpas (2003) both methods were applied on 1'×1' gravity data and 30''×30'' grids of height to geoid determination of different regions of the USA. The results indicated that the Moritz-Pellinen method is clearly superior to Vanicek-Martinec method. However, in this study, our goal is not to evaluate the effectiveness of these two methods. The subject of this study is the propagation of DEM error in the direct and indirect topographical effects in geoid using the planar approximation of the Moritz-Pellinen method. The integral formulas of standard deviation of the topographical effects were obtained in terms of DEM standard deviation error and error covariance function.    To increase performance, all numerical calculations of all derived integrals were performed by FFT. Numerical investigations of this study are done over the central Alborz mountainous area, as this area is the most rugged terrain in Iran. Two global DEMs, the SRTM and the AW3D30, were freely available with a spatial resolution of one arc second (approximately 30 meters) in the test region. The mean and standard deviation of differences between two DEMs are about 2 and 3 meters, respectively, which produce 0.1 mGal and 1 mm differences in DTE and ITE.Estimation of DTE and ITE error requires the global average error (standard deviation) of the DEM as well as the parameter of correlation length for evaluation of correlated error. Accurate estimation of these parameters needs high-resolution ground control points that were not available in this study. Therefore, using an overall accuracy and a correlation length based on the previous studies, the estimated standard deviation for direct and indirect topographical effects varied from 0 to 0.6 mGal and 0 to 17 mm in the test region, respectively.    The influence of DTE error on the geoid error can be computed by applying the error propagation law on the Stokes’ integral. Our calculations show that the error of SRTM DEM on geoid in central Alborz can exceed from 1 cm, but the values are about 1-2 mm in the flat areas. Therefore, geoid determination with 1 cm accuracy in mountainous areas in Iran requires DEM with better average accuracy than the current available models. Various previous studies indicate that the error of DEMs decreases in mountainous areas.

Volcanic eruptions are usually done by increasing magma pressure. Monitoring this process in real-time can provide useful information for predicting eruptions. The cross-correlation function of ambient seismic noises has been used many times to monitor the activity of volcanoes around the world. Still, this method is usually limited to volcanoes equipped with large networks and broadband stations.   In this article, a technique has been proposed that automatically and without the need for advanced equipment or lots of data can calculate a cross-correlation function of seismic waves, then using the calculated cross-correlation function, it analyzes and examines the temporary changes in the relative velocity of seismic waves as well as the anomaly of the amplitude ratio of continuous data recorded in all pairs of stations as two eruption attributes.The SARA (Seismic Amplitude Ratio Analysis) method was used to investigate the changes in the amplitude ratio, and the MWCS (Moving-Window Cross-Spectral) method was used to calculate the relative speed of environmental seismic wave data. Both methods have been implemented using MSNoise software package.   In order to validate these methods, the continuous data of 5 seismic stations near Etna volcano in Italy were used. First, in order to process the data, daily vertical recordings of all stations were divided into 30-minute segments. Then, the segments were demeaned, tapered and normalized to three times the root-mean-square (RMS). Next, the daily cross-correlation between all pairs of stations was calculated and the cross-correlation function was filtered in different frequency ranges. Finally, the velocity variations were measured with the MWCS method. The results showed a decrease of about 0.2 percent in the velocity before the main eruption and an increase rapidly after the eruption.   In the second step, the amplitude ratio of all pairs of stations was calculated with the SARA method. The increasing trend of the amplitude ratio was observed from three hours before the main eruption. To quantify the results, the Mann-Kendall trend analysis test was used for all pairs of stations. By using Sen's slope estimation test, the slope value of each figure was calculated separately. The results showed a temporary increase in the seismic amplitude ratio in 90 percent of pairs of stations before the main eruption. Automatic and continuous measurement of these attributes and combining their results can show the potential of this method to improve volcano monitoring and eruption early warning for active volcanoes.

Mud volcanoes are natural phenomena that provide an essential source of information about subsurface sediments and deep structures. The phenomenon is usually associated with hydrocarbon accumulations in deep-seated strata. More than 30% of all mud volcanoes in the world are concentrated in the South Caspian Basin. Gorgan plain, as a part of the south Caspian lowland, is a transition zone between uplifting zones of the Alborz and Kopet Dagh and the subsiding basin of the south Caspian. Four active mud volcanoes in the western parts of the Gorgan Plain have extrusion of gas and mud. The existence of the possible hydrocarbon contents in this plain caused a reflection seismic survey and exploratory wells were performed in this area by the National Iranian Oil Company. In this paper, we used 2-D reflection seismic data and well top data for the investigation of stratigraphy and structural setting of the Neftlijeh and Gharnyaregh mud volcanoes. According to the Well Report, the area sediments are composed of the Tertiary to Quaternary sediments of the SCB and underlying pre-Tertiary sequence of the Kopet-Dagh basin and a missing Oligocene, Eocene, Paleocene and upper Cretaceous deposition are observed in the well. The interpretation of the seismic section shows that the Caspian basin deposits reveal a partial deformation and increasingly sloping toward the depocenter, while the sequence of Kopet Dagh is folded. The Neftlijeh and Gharnyaregh mud volcanoes occurred on subsurface anticline axes of the Kopet Dagh and a cluster of conjugate normal faults developed into the Cenozoic formations above the hinge zone of these anticlines. The subsidence pattern is observable at the summit of the anticlines. The structure suggests the presence of a chamber within the crest of the anticline. It seems extrusion and material removal from this chamber caused subsidence and forming of the structure. The Oligo-Miocene Maykop Formation is the significant source of both the extruded mud and the petroleum in the south Caspian basin, which is not observed in the studied well due to later regional erosion. However, the Cheleken and Apsheron deposits, known as reservoir rocks, have a large thickness in the area. The Kashafrud Formations are considered as the main source rock for the Kopet Dagh basin and the Mozduran and Tirgan formations are known as reservoir rocks. The occurrence of the Late Eocene compressional tectonic phase and following the folding of the Mesozoic sedimentary created structural traps at the strata. In addition, continued diapirism and uplifting of the deep-seated strata led to the growth of extensional faults and fractures over the hinge zones. These structures provide effective pathways for gas and fluid ascent from deep reservoirs to the surface. Generally, the results suggest that these mud volcanoes have a spatial and genetic relationship with buried folds. It seems the location of Gharenyaregh and Neftelijeh mud volcanoes is controlled by subsurface anticlines and their feeding source originated from both the Tertiary (SCB) and Pre-Tertiary (Kopet Dagh) units.

The terrestrial ecosystem plays an important role in the carbon cycle and each year absorbs more than a quarter of human carbon emissions, which is called terrestrial carbon sinks. In the last few decades, carbon sources and sinks in West Asia and around the Mediterranean Sea have changed due to drastic changes in land cover due to economic development and urbanization growth. In the present study, using the observations-based CO2 flux data of Jena CarboScope Institute, temperature and precipitation data, the seasonal and annual pattern of CO2 exchanges during the period 1982-2019, has been investigated, as well as the role of teleconnection patterns on the CO2 flux fluctuations was analyzed. The results showed that on long term average, the land areas of the northern Mediterranean Sea were CO2 sinks with absorption up to -114 g.C/(m2.year) and the amount of CO2 absorption in this areas have decreased with a trend of up to 5 g.C/(m2.year.decade) during the study period. While the CO2 sinks in the western parts of India (up to -70 g.C/(m2.year)) increased with the trend of up to -8 g.C/(m2.year.decade). Also, the central regions (including Iran, Saudi Arabia and the northern parts of Africa), the northeast (including Afghanistan, Turkmenistan and Tajikistan) and the southwest (including the central regions of Africa) of the study area, which were the CO2 sources on average (between 0 to 50 g.C/(m2.year)), the intensity of CO2 emissions has been reduced with a trend of up to -10 g.C/(m2.year.decade). Based on the results, in the land areas of the northern Mediterranean Sea, Turkmenistan, Tajikistan and the coastal areas of the Caspian Sea in Iran (western parts of India, western Iran and central Africa) in the study area, seasonal changes in temperature (precipitation) played a more important role in the seasonal cycle of CO2 exchanges between the atmosphere and the terrestrial ecosystem. The positive correlation between the MEI.v2 index related to El Niño/Southern Oscillation (ENSO) and the variability of the atmosphere-land CO2 flux showed that in El Niño conditions (positive and warm phase of ENSO) the amount of CO2 absorption and sink in the land areas of the northern Mediterranean Sea and West India, Southeast Iran and Pakistan decreased, which can be due to the decrease in rainfall in El Niño conditions in these areas. In La Niño conditions (negative and cold phase of ENSO) in these areas, the amount of CO2 absorption increased and the sinks became stronger. The negative correlation of atmospheric-land CO2 flux variability with both El Niño/Southern Oscillation and Indian Ocean Dipole Oscillation showed that in El Niño and positive IOD conditions, CO2 emission decreased in the western and central parts of Africa in the study area, while in La Niño and negative IOD conditions CO2 emission increased in these regions. Also, in the positive phase of IOD, the CO2 sink in the eastern part of Iran, Afghanistan, Turkmenistan, Tajikistan, the southeastern regions of Iran, southern Pakistan, and western parts of India became weaker, and in the negative phase of IOD, the amount of CO2 absorption in these areas increased.