Time-dependent seismic hazard analysis for the Greater Tehran and surrounding areas

This study presents a time-dependent approach for seismic hazard in Tehran and surrounding areas. Hazard is evaluated by combining background seismic activity, and larger earthquakes may emanate from fault segments. Using available historical and paleoseismological data or empirical relation, the recurrence time and maximum magnitude of characteristic earthquakes for the major faults have been explored. The Brownian passage time (BPT) distribution has been used to calculate equivalent fictitious seismicity rate for major faults in the region. To include ground motion uncertainty, a logic tree and five ground motion prediction equations have been selected based on their applicability in the region. Finally, hazard maps have been presented.     

Soil genesis and clay mineralogy on Aliabbas River Alluvial Fan, Kerman Province

Alluvial fan is among the important geomorphic positions in arid and semi-arid environments, and the history of settlement in central parts of Iran plateau has significantly been related to this landform. Soil properties are also related to the stability and the position of geomorphic surfaces. To study and compare clay mineralogy and soil physicochemical responses to geomorphic positions, 11 representative pedons on stable and unstable alluvial fan surfaces and plain geomorphic position in a transect from Sarcheshmeh Mountains toward Rafsanjan Plain were studied. Soil moisture and temperature regimes of the area were aridic and mesic, respectively. Smectite, kaolinite, chlorite, illite, and palygorskite clay minerals were found in almost all the studied soils. More salinity was investigated in stable alluvial fan surfaces than unstable positions. Evidence of a more humid paleoclimate shown by buried Bt horizons in plain surface was observed. Transformation of palygorskite to smectite in surface horizon of unstable alluvial fan position and preservation of palygorskite associated by gypsum crystals in By horizon of stable fan surfaces were among the important findings of the research. There was a significant and mutual relationship between geomorphology and physicochemical and mineralogical properties of soils under study.     

Adaptive state estimation of groundwater contaminant boundary input flux in a 2-dimensional aquifer

In many circumstances involving heat and mass transfer issues,it is considered impractical to measure the input flux and the resulting state distribution in the domain.Therefore,the need to develop techniques to provide solutions for such problems and estimate the inverse mass flux becomes imperative.Adaptive state estimator(ASE)is increasingly becoming a popular inverse estimation technique which resolves inverse problems by incorporating the semi-Markovian concept into a Bayesian estimation technique,thereby developing an inverse input and state estimator consisting of a bank of parallel adaptively weighted Kalman filters.The ASE is particularly designed for a system that encompasses independent unknowns and/or random switching of input and measurement biases.The present study describes the scheme to estimate the groundwater input contaminant flux and its transient distribution in a conjectural two-dimensional aquifer by means of ASE,which in particular is because of its unique ability to efficiently handle the process noise giving an estimation of keeping the relative error range within 10%in 2-dimensional problems.Numerical simulation results show that the proposed estimator presents decent estimation performance for both smoothly and abruptly varying input flux scenarios.Results also show that ASE enjoys a better estimation performance than its competitor,Recursive Least Square Estimator(RLSE)due to its larger error tolerance in greater process noise regimes.ASE's inherent deficiency of being slower than the RLSE,resulting from the complexity of algorithm,was also noticed.The chosen input scenarios are tested to calculate the effect of input area and both estimators show improved results with an increase in input flux area especially as sensors are moved closer to the assumed input location.     

Statistical analysis of stress transmission in wet granular materials

The micromechanics of wet granular materials encompasses complex microstructural and capillary interconnects that can be readily described through a formal derivation of stress transmission in such a 3‐phase medium. In the quest for defining an appropriate stress measure, the stress tensor expression that results from homogenization [Duriez et al. J Mech Phys Solids 99 (2017): 495‐511] of such a medium provides theoretical insights necessary to extract useful information on the relationship between capillary effects and microforce interactions via several small‐scale parameters whose evaluation can be challenging. Using instead a statistical approach where microvariable distributions are described by probability density functions, the current study provides simple estimates of stress components in terms of only a few tractable microvariables such as coordination number and fabric anisotropy. In particular, the latter recognizes details of contacts such as force interactions being either mechanical or capillary, including interactions with and without mechanical contact. The developed expressions are in a good agreement with discrete element method simulation results of the triaxial loading of a wet granular assembly, notably for hydrostatic (mean) pressure. A new set of dimensionless groups is also identified to characterize the significance of mechanical and capillary physics, which facilitates a better understanding of the contribution of dominating elements to stress, while also providing the opportunity to incorporate important capillary effects in micromechanically based constitutive formulations.     

On regularized time varying gravity field models based on grace data and their comparison with hydrological models

Determination of spherical harmonic coefficients of the Earth’s gravity field is often an ill-posed problem and leads to solving an ill-conditioned system of equations. Inversion of such a system is critical, as small errors of data will yield large variations in the result. Regularization is a method to solve such an unstable system of equations. In this study, direct methods of Tikhonov, truncated and damped singular value decomposition and iterative methods of ν, algebraic reconstruction technique, range restricted generalized minimum residual and conjugate gradient are used to solve the normal equations constructed based on range rate data of the gravity field and climate experiment (GRACE) for specific periods. Numerical studies show that the Tikhonov regularization and damped singular value decomposition methods for which the regularization parameter is estimated using quasioptimal criterion deliver the smoothest solutions. Each regularized solution is compared to the global land data assimilation system (GLDAS) hydrological model. The Tikhonov regularization with L-curve delivers a solution with high correlation with this model and a relatively small standard deviation over oceans. Among iterative methods, conjugate gradient is the most suited one for the same reasons and it has the shortest computation time.     

Recent development of the earthquake strong motion-intensity catalog and intensity prediction equations for Iran

This study aims to develop a new earthquake strong motion-intensity catalog as well as intensity prediction equations for Iran based on the available data. For this purpose, all the sites which had both recorded strong motion and intensity values throughout the region were first searched. Then, the data belonging to the 306 identified sites were processed, and the results were compiled as a new strong motion-intensity catalog. Based on this new catalog, two empirical equations between the values of intensity and the ground motion parameters (GMPs) for the Iranian earthquakes were calculated. At the first step, earthquake “intensity” was considered as a function of five independent GMPs including “Log (PHA),” “moment magnitude (M_W),” “distance to epicenter,” “site type,” and “duration,” and a multiple stepwise regression was calculated. Regarding the correlations between the parameters and the effectiveness coefficients of the predictors, the Log (PHA) was recognized as the most effective parameter on the earthquake “intensity,” while the parameter “site type” was removed from the equations since it was determines as the least significant variable. Then, at the second step, a simple ordinary least squares (OLS) regression was fitted only between the parameters intensity and the Log (PHA) which resulted in more over/underestimated intensity values comparing to the results of the multiple intensity-GMPs regression. However, for rapid response purposes, the simple OLS regression may be more useful comparing to the multiple regression due to its data availability and simplicity. In addition, according to 50 selected earthquakes, an empirical relation between the macroseismic intensity (I₀) and M_W was developed.     

Wavelet and Gaussian Approaches for Estimation of Groundwater Variations Using GRACE Data

In this study, a scheme is presented to estimate groundwater storage variations in Iran. The variations are estimated using 11 years of Gravity Recovery and Climate Experiments (GRACE) observations from period of 2003 to April 2014 in combination with the outputs of Global Land Data Assimilation Systems (GLDAS) model including soil moisture, snow water equivalent, and total canopy water storage. To do so, the sums of GLDAS outputs are subtracted from terrestrial water storage variations determined by GRACE observations. Because of stripping errors in the GRACE data, two methodologies based on wavelet analysis and Gaussian filtering are applied to refine the GRACE data. It is shown that the wavelet approach could better localize the desired signal and increase the signal‐to‐noise ratio and thus results in more accurate estimation of groundwater storage variations. To validate the results of our procedure in estimation of ground water storage variations, they are compared with the measurements of pisometric wells data near the Urmia Lake which shows favorable agreements with our results.     

Palaeoecological,sedimentological and stratigraphical insights into microbially induced sedimentary structures of the lower Cambrian successions of Iran

Micro-organisms producing microbially induced sedimentary structures, particularly epibenthic cyanobacteria, are not facies-dependent and could flourish in any environment if appropriate ecological conditions were provided. Hence, the changes in environmental parameters are the controlling factors on ecological tolerance of the producers. This study on the lower Cambrian successions of the Lalun Formation in Central Iran shows that paralic environments reacted differently to changes in parameters such as river and tide energy, palaeo-topography, the rate of sediment supply and fluctuations in sea-level, even though all were characterized by sandy substrates suitable for the development of microbially induced sedimentary structures. Therefore, the abundance and preservation of microbially induced sedimentary structures varied in the different paralic environments. From a sequence stratigraphic viewpoint, this study demonstrates that erosional discontinuities lacked the conditions required for the substrate stabilization by microbial communities. The distribution, size and type of microbially induced sedimentary structures within high frequency cycles generally follow the trends of changes in vertical facies stacking patterns. Within systems tracts, the pattern, morphological diversity and size of microbially induced sedimentary structures are not dependent on the type of systems tract, but on the type of depositional system developed such as delta, incised valley, coastal plain, estuaries and shoreline to shelf systems. Generally, estuarine and peritidal carbonates record an increase in the development of mat colonization during the transgressive systems tract, owing to decreased sedimentation rate as well as extended shallow water habitats. In contrast, the existence of microbially induced sedimentary structures depends on the pattern of shoreline shift in depositional systems developed during the highstand systems tract, such as open coast tidal flat and delta environments. If a shoreline regression was continuous (depositional trend and stacking pattern are a set of high frequency cycles), a greater increase in the aggradational component than the progradational component would cause intensified destructive processes hindering the development of microbial communities.