SOM-DRASTIC: using self-organizing map for evaluating groundwater potential to pollution

Groundwater is considered as the most important water resource, especially in arid and semi-arid regions, so it is crucial to impede this source of water to be contaminated. One of the most common methods to assess groundwater vulnerability is DRASTIC method. However, the subjectivity existing in defining DRASTIC weights and ratings as well as inadaptability of the parameters involved in this method with special geology, hydrogeology, land use and climatic conditions have urged researchers to modify this method. In this paper, a new method combining a special type of the neural networks called Self-Organizing Map (SOM) and the traditional DRASTIC model resulting in the hybrid SOM-DRASTIC model is applied to modify and improve DRASTIC Model. The traditional DRASTIC method holds a summation among all negative effects of different factors contributing to vulnerability, while the proposed hybrid method is able of classifying the groundwater vulnerability and deriving the real relation existing between the DRASTIC parameters as the inputs and the vulnerability class as the output of the method. The vulnerability assessment process was performed on the Zayandeh-Rud river basin aquifers in Iran. The SOM-DRASTIC identified the northern parts of the study area as the most vulnerable areas with a drastically fractured structure, while the traditional DRASTIC ranked the western parts as the most vulnerable regions with a high rate of net recharge. The results demonstrate that the proposed method can be used by managers and decision-makers as an alternative robust tool for vulnerability-based classification and land use planning.     

A new solution to estimate the time delay on the topographic site using time domain 3D boundary element method

This study focuses on investigating spatial variation of ground motion that has great influence on the dynamic behavior of the large structures located on the surface topography. One of the most effective parameters on the spatial variation of ground motion is the difference between the arrival time of seismic waves in different points located on the abutments. In this research, a three-dimensional model of the Pacoima Dam site is prepared. The time domain 3 D boundary element method is used to apply non-uniform excitation at the dam supports. This model is subjected to vertically propagating incident SH and P waves. The time delay can be characterized by calculating the value of the time delay for which the cross-correlation between two records is maximized. Finally, to obtain the time delay in a topographic site, a function considering effective parameters such as the height from the canyon base, wave velocity and predominant frequency, is presented. Furthermore, a code was developed for generating the spatially variation of seismic ground motions. The results show that the proposed functions have an acceptable accuracy in estimating the time delay to generate non-uniform ground motion.     

Paleoseismological Analysis Along the Astara Fault System (Talesh Mountain, North Iran)

The Astara Fault System(AFS) is located in the northwest Alborz, east of Talesh Mountain(TM) and west of the South Caspian Basin(SCB). The AFS is one of the basement rock faults in Iran that is heavily involved in seismotectonic activity of the Talesh region, and to which subsidence of the SCB is attributed. There is little information available concerning previous AFS seismic activities and its properties. In order to elucidate the seismic behavior and activities of the AFS, we conducted a research study on paleoseismology of the fault. Based on paleoseismic evidence, two scenarios could be taken into consideration, one of which has three and another has four seismic events with magnitudes Mw in the range of 6.7 to 7.2. Evidence of these seismic events is within sedimentary succession as they have occurred during the past 3 ka(this age is determined based on the deposition rate of the region). Six carbon samples were taken for C~(14) age determination tests, the results of which clearly demonstrated that the EvIV(scenario A) and EvⅢ(scenario B) had occurred before 27,444 cal BP, while other events occurred in the time period between 27,444 cal BP and 3 ka ago. If we consider the occurrence of three or four seismic events(based on the two scenarios) to be between 27,444 cal BP and 3 ka ago, the average recurrence interval is 7,119 ± 1,017, but evidence for these events has been removed. If we assume EvI to be the youngest event(in both scenarios), the minimum elapsed time is therefore 3 ka.     

Petrogenesis of Rabor-Lalehzar magmatic rocks (SE Iran): Constraints from whole rock chemistry and Sr-Nd isotopes

The Urumieh-Dokhtar magmatic arc (UDMA) of Central Iran has been formed during Neotethyan Ocean subduction underneath Eurasia. The Rabor-Lalehzar magmatic complex (RLMC), covers an area ～1000?km² in the Kerman magmatic belt (KMB), SE of UDMA. RLMC magmatic rocks include both granitoids and volcanic rocks with calc-alkaline and adakitic signatures but with different ages.Miocene adakitic rocks are characterd by relatively enrichmented in incompatible elements, high (Sr/Y)_(N) (>40), and (La/Yb)_(N) (>10) ratios with slightly negative Eu anomalies (Eu_N/Eu*≈ 0.9), depletion in HFSEs, and relatively non-radiogenic Sr isotope signatures (⁸⁷Sr/⁸⁶Sr?=?0.7048–0.7049). In contrast, the Oligocene granitoids exhibit low Sr/Y (<20) and La/Yb (<9) ratios, negative Eu anomalies (Eu_N/Eu*?≈?0.5), and enrichment in HFSEs and radiogenic Sr isotope signatures (⁸⁷Sr/⁸⁶Sr?=?0.7050–0.7052), showing affinity to the island arc rocks. Eocene volcanic rocks which crusscut the younger granitoid rocks comprise andesites and dacites. Geochemically, lavas show calc-alkaline character without any Eu anomaly (Eu_N/Eu*?≈?1.0). Based on the geochemical and isotopic data we propose that melt source for both calc-alkaline and adakitic rocks from the RLMC can be related to the melting of a sub-continental lithospheric mantle (SCLM). Basaltic melts derived from a metasomatized mantle wedge might be emplaced at the mantle-crust boundary and formed the juvenile mafic lower crust. However, some melts fractionated in the shallow magma chambers and continued to rise forming the volcanic intermediate-mafic rocks at the surface. On the other hand, the assimilation and fractional crystallization in the shallow magma chambers of may have been responsible for the development of Oligocene granitoids with calc-alkaline affinity. In the mid-Late Miocene, following the collision between Afro-Arabia and Iranian block the juvenile mafic crust of UDMA underwent thickening and metamorphosed into garnet-amphibolites. Subsequent upwelling of a hot asthenosphere during Miocene was responsible for partial melting of thickened juvenile crust of the SE UDMA (RLM complex). The adakitic melts ascended to the shallow crust to form the adakitic rocks in the KMB.     

A new depression‐dominated delineation (D‐cubed) method for improved watershed modelling

Prior to hydrologic modelling, topographic features of a surface are derived, and the surface is divided into sub‐basins. Surface delineation can be described as a procedure, which leads to the quantitative rendition of surface topography. Different approaches have been developed for surface delineation, but most of them may not be applicable to depression‐dominated surfaces. The main objective of this study is to introduce a new depression‐dominated delineation (D‐cubed) method and highlight its unique features by applying it to different topographic surfaces. The D‐cubed method accounts for the hierarchical relationships of depressions and channels by introducing the concept of channel‐based unit (CBU) and its connection with the concept of puddle‐based unit (PBU). This new delineation method implements a set of new algorithms to determine flow directions and accumulations for puddle‐related flats. The D‐cubed method creates a unique cascaded channel‐puddle drainage system based on the channel segmentation algorithm. To demonstrate the capabilities of the D‐cubed method, a small laboratory‐scale surface and 2 natural surfaces in North Dakota were delineated. The results indicated that the new method delineated different surfaces with and without the presence of depressional areas. Stepwise changes in depression storage and ponding area were observed for the 3 selected surfaces. These stepwise changes highlighted the dynamic filling, spilling, and merging processes of depressions, which need to be considered in hydrologic modelling for depression‐dominated areas. Comparisons between the D‐cubed method and other methods emphasized the potential consequences of use of artificial channels through the flats created by the depression‐filling process in the traditional approaches. In contrast, in the D‐cubed method, sub‐basins were further divided into a number of smaller CBUs and PBUs, creating a channel‐puddle drainage network. The testing of the D‐cubed method also demonstrated its applicability to a wide range of digital elevation model resolutions. Consideration of CBUs, PBUs, and their connection provides the opportunity to incorporate the D‐cubed method into different hydrologic models and improve their simulation of topography‐controlled runoff processes, especially for depression‐dominated areas.     

Analysis of refracturing in horizontal wells: Insights from the poroelastic displacement discontinuity method

In this paper, a fully coupled 2‐dimensional poroelastic displacement discontinuity method is used to investigate the refracturing process in horizontal wells. One of the objectives of refracturing is to access new reserves by adding new hydraulic fractures in zones that were bypassed in the initial fracturing attempt. Pore pressure depletion in the vicinity of old fractures directly affects the state of stress and eventually the propagation of newly created hydraulic fractures. Thus, a poroelastic analysis is required to identify guidelines for the refracturing process, in particular to understand the extension of the pore pressure depletion, and eventually, the orientation of new as well as old fractures. We propose a fully coupled approach to model the whole process of child fracture propagation in a depleted area between 2 parent fractures in the same wellbore. This approach omits the need of using multistep workflow that is regularly used to model the process. The maximum tensile stress criterion (σ criterion) is used for hydraulic fracture propagation. The proposed method is verified using available analytical solutions for total stress and pore pressure loading modes on a line fracture in drained and undrained conditions. Then, test cases of multifractured horizontal wells are studied to calculate the time evolution of the stress and pore pressure fields around old fractures and to understand the effect of these fields on the propagation path of newly created fractures. Finally, the effect of the pore pressure depletion on the propagation path of the newly created fractures in the bypassed area of the same wellbore is studied. The results show that the depleted areas around old fractures are highly affected by the extent and severity of the stress redistribution and pore pressure depletion. It is observed that a successful creation of new fractures may only happen in certain time frames. The results of this study provide new insights on the behavior of newly created fractures in depleted zones. They also clarify the relationship between stress change and pore pressure depletion in horizontal wells.     

The Temperature – Magnetic Field Relation in Observed and Simulated Sunspots

Observations of the relation between continuum intensity and magnetic field strength in sunspots have been made for nearly five decades. This work presents full-Stokes measurements of the full-split (\(g = 3\)) line Fe i 1564.85 nm with a spatial resolution of \(0.5^{\prime\prime}\) obtained with the GREGOR Infrared Spectrograph in three large sunspots. The continuum intensity is corrected for instrumental scattered light, and the brightness temperature is calculated. Magnetic field strength and inclination are derived directly from the line split and the ratio of Stokes components. The continuum intensity (temperature) relations to the field strength are studied separately in the umbra, light bridges, and penumbra. The results are consistent with previous studies, and it was found that the scatter of values in the relations increases with increasing spatial resolution thanks to resolved fine structures. The observed relations show trends common for the umbra, light bridges, and the inner penumbra, while the outer penumbra has a weaker magnetic field than the inner penumbra at equal continuum intensities. This fact can be interpreted in terms of the interlocking comb magnetic structure of the penumbra. A comparison with data obtained from numerical simulations was made. The simulated data generally have a stronger magnetic field and a weaker continuum intensity than the observations, which may be explained by stray light and limited spatial resolution of the observations, and also by photometric inaccuracies of the simulations.     

Effect of climate change on sea water intrusion in coastal aquifers

There is increasing debate these days on climate change and its possible consequences. Much of this debate has focused in the context of surface water systems. In many arid areas of the world, rainfall is scarce and so is surface runoff. These areas rely heavily on groundwater. The consequences of climate change on groundwater are long term and can be far reaching. One of the more apparent consequences is the increased migration of salt water inland in coastal aquifers. Using two coastal aquifers, one in Egypt and the other in India, this study investigates the effect of likely climate change on sea water intrusion. Three realistic scenarios mimicking climate change are considered. Under these scenarios, the Nile Delta aquifer is found to be more vulnerable to climate change and sea level rise. Copyright © 1999 John Wiley & Sons, Ltd.     

Site dependence and record selection schemes for building fragility and regional loss assessment

When performing loss assessment of a geographically dispersed building portfolio, the response or loss (fragility or vulnerability) function of any given archetype building is typically considered to be a consistent property of the building itself. On the other hand, recent advances in record selection have shown that the seismic response of a structure is, in general, dependent on the nature of the hazard at the site of interest. This apparent contradiction begs the question: Are building fragility and vulnerability functions independent of site, and if not, what can be done to avoid having to reassess them for each site of interest? In the following, we show that there is a non‐negligible influence of the site, the degree of which depends on the intensity measure adopted for assessment. Employing a single‐period (e.g., first‐mode), spectral acceleration would require careful record selection at each site and result to significant site‐to‐site variability of the fragility or vulnerability function. On the other hand, an intensity measure comprising the geometric mean of multiple spectral accelerations considerably reduces such variability. In tandem with a conditional spectrum record selection that accounts for multiple sites, it can offer a viable approach for incorporating the effect of site dependence into fragility and vulnerability estimates. Copyright © 2017 John Wiley & Sons, Ltd.     

Development of fragility curves by incorporating new spectral shape indicators and a weighted damage index: case study of steel braced frames in the city of Mashhad,Iran

In this study, strong ground motion record(SGMR) selection based on Eta(η) as a spectral shape indicator has been investigated as applied to steel braced frame structures. A probabilistic seismic hazard disaggregation analysis for the definition of the target Epsilon(ε) and the target Eta(η) values at different hazard levels is presented, taking into account appropriately selected SGMR's. Fragility curves are developed for different limit states corresponding to three representative models of typical steel braced frames having significant irregularities in plan, by means of a weighted damage index. The results show that spectral shape indicators have an important effect on the predicted median structural capacities, and also that the parameter η is a more robust predictor of damage than searching for records with appropriate ε values.