CSRMT measurements in the frequency range of 1–250 kHz to map a normal fault in the Volvi basin, Greece

In order to gain a better understanding of the geometry of surface faults, five Controlled Source/Radio Magnetotelluric (CSRMT) profiles were measured across the Volvi basin, 45 km northeast of the city of Thessaloniki in Greece. The data were collected in two frequency ranges: a) 1–12.5 kHz using a remotely controlled double horizontal magnetic dipole transmitter (CSAMT measurements), and b) 15–250 kHz using the signal from distant radio transmitters (RMT measurements). The transition from the RMT band to the CSAMT band was smooth and continuous allowing us to combine both datasets for plane-wave modeling. The surface geology shows a predominantly 2D structure, and therefore we planned the survey into profiles perpendicular to the geological strike. We have used a 2D interpretation tool to model the data in TE, TM, TE + TM and determinant modes. Using a 4% error floor on the impedance, 2D resistivity models from inversion of the determinant data provide lower RMS data fits (4.2 and 1.2 for resistivity and phase, respectively) compared to the combined TE + TM data (4.4, 2.8, overall resistivity and phase, respectively). 2D inversion of the measured tensor data shows a sharp change in the depth to the top of resistive gneiss–schist basement that is overlain by a less resistive overburden at southern basin flanks. The change in depth to the bedrock is clearly seen in all 2D models along the measured profiles suggesting the existence of normal faults with strike directions of NE–SW to E–W. The 2D electrical resistivity models suggest that the bedrock deepens towards south-west. The resistivity models are also compared with the existing borehole information in the area and show a reasonable correlation. For example the sharp change of depth to the bedrock towards the center of the basin as seen in the resistivity models are also confirmed by the borehole data.     

Assessment of Various Fuzzy c-Mean Clustering Validation Indices for Mapping Mineral Prospectivity: Combination of Multifractal Geochemical Model and Mineralization Processes

This paper describes the application of an unsupervised clustering method, fuzzy c-means (FCM), to generate mineral prospectivity models for Cu?±?Au?±?Fe mineralization in the Feizabad District of NE Iran. Various evidence layers relevant to indicators or potential controls on mineralization, including geochemical data, geological–structural maps and remote sensing data, were used. The FCM clustering approach was employed to reduce the dimensions of nine key attribute vectors derived from different exploration criteria. Multifractal inverse distance weighting interpolation coupled with factor analysis was used to generate enhanced multi-element geochemical signatures of areas with Cu?±?Au?±?Fe mineralization. The GIS-based fuzzy membership function MSLarge was used to transform values of the different evidence layers, including geological–structural controls as well as alteration, into a [0–1] range. Four FCM-based validation indices, including Bezdek’s partition coefficient (V_Pc) and partition entropy (V_Pe) indices, the Fukuyama and Sugeno (V_FS) index and the Xie and Beni (V_XB) index, were employed to derive the optimum number of clusters and subsequently generate prospectivity maps. Normalized density indices were applied for quantitative evaluation of the classes of the FCM prospectivity maps. The quantitative evaluation of the results demonstrates that the higher favorability classes derived from V_FS and V_XB (N_d?=?9.19) appear more reliable than those derived from V_Pc and V_Pe (N_d?=?6.12) in detecting existing mineral deposits and defining new zones of potential Cu?±?Au?±?Fe mineralization in the study area.

     

Long-term improvement of agricultural vegetation by floodwater spreading in the Gareh Bygone Plain,Iran. In the pursuit of human security,is artificial recharge of groundwater more lucrative than selling oil?

In southern Iran’s Gareh Bygone Plain, water-supply qanats in four mixed farming communities were desiccated by over-pumping of illegal dug wells throughout the area. Emergency situations developed, resulting in city-ward migration. Since 1983, 193 million m³ of water has been supplied to those communities by floodwater spreading (FWS) to facilitate spate irrigation of sandy rangeland (2,034 ha) and artificial recharge of groundwater (ARG), of which 76 % has recharged the aquifer. This resulted in a reverse migration of the population. The irrigated area in the 2010–2011 growing season increased 13.2 fold when compared to the pre-FWS period, and year-round forage for about 700 sheep has been provided since 1991. The ARG is a logical alternative to building large dams in Iran; 420,000 km² of coarse-grained alluvium provides capacity to store 5,000 km³ of water, representing more than ten times the annual precipitation of the whole country. As the equivalent cost for building dams to accommodate that volume is estimated at US$12.5?×?10¹², the potential value of the alluvium may be realized. ARG on the recharge areas of 33,000 of the desiccated qanats eventually could rejuvenate them. As agricultural commodities absorb 19 % of the monetary value of Iran’s imports, and ARG activities could supply the water to produce them, alluvium is even more valuable than oil, which provides foreign exchange. More importantly, ARG on 140,000 km² of the alluvium could strengthen the capacity to adapt to droughts and reduce the number and impact of water-related emergency situations.     

A recent scenario of mass wasting and its impact on the transportation in Alborz Mountains, Iran using geo-information technology

Mass movements or mass wasting is being considered as one of the severe forms of natural disasters. Iran is geographically located in the Alps–Himalaya seismicity belt. It has a high potential to mass wasting. This seismic phenomenon creates landslides and rock falls in the high mountains of Alborz and Zagros. These mass movements and various types of slides can be systematically assessed and mapped through traditional mapping frameworks using geo-information technologies. The geo-information-based technology offers the earth scientist to study and map various types of mass movement and stability of slopes. In this study, we used field data coupling with the tectonic-related factors to provide a solution for slope-related hazards. Firstly, various geological and geomorphological factors such as lineaments and faults, vegetation, lithology, slope, drainage, land use/land cover, seismicity and roads network were extracted and compiled using geo-information technology. This is because the factors mentioned above play important role in the instability of the region. Then, the study area was divided into four regions based on the rate of mass wasting and its degree of vulnerability. The results of this study showed that the erosion in Karaj formation is severe. Additionally, this research also reveals that the hydrothermal solutions caused by the erosional activities have influenced the glassy element of tuffs and subsequently changed into the clays. This change has caused the tuffs to be relatively unstable. Further, it is evident that the chemical and physical weathering has had a big impact on it whilst most of the mass wasting has occurred within the unstable tuffs of Karaj formation. Finally, the paper concluded that the recent construction of the new roads in the region has increased the potential danger for generating the mass wastes and thus makes the region more unstable.     

Using velocimeter signal to noise ratio as a surrogate measure of suspended mud concentration

This study examines the relationship between suspended sediment concentration (SSC) and the signal to noise ratio (SNR) recorded by a 6 MHz Nortek Vector velocimeter in a laboratory water tank using four different synthetic and natural mud mixtures and different combinations of the user-set Vector parameters transmit power level and velocity range. For concentrations less than 1500 mg/l (1.5 g/l), a region of linearity between the logarithm of concentration and time-average SNR was found for all sediment types and transmitter power level settings. Within this concentration range, the experimental data was used to develop calibrated equations of the form, log(SSC)=c₁SNR+c₂; R² values for all calibrated equations were greater than 0.98, suggesting that properly calibrated relations can yield accurate time-averaged SSC measurements using Vector measured SNR. An analysis of the general calibration equation indicated that the predicted SSC values are sensitive to changes in the coefficient values for c₁ and c₂. Even small (10%) deviations in coefficient values resulted in 20%-65% changes in the predicted SSC. Variation in c₁ and c₂ values among all four mud mixtures were significant enough that the calibrated equations could not be used interchangeably. This was true even among three samples that had similar particle-size distributions. Translation of raw 32 Hz SNR data to 32 Hz SSC time series produced excessively large variation in the SSC time series. Several smoothing and filtering schemes were examined to reduce the magnitude of these fluctuations to more reasonable levels. Of the methods tested, a two-sided moving average functioned best at removing fine-scale variation while retaining larger-scale trends. A 96-point (3 Hz) averaging window brought 98.6% of the Vector estimated SSC time series values to within ±10% of the time-average physical samples. Impacts of turbulent kinetic energy and sampling volume size on instrument recorded SNR were also empirically examined.     

Earthquake Potential in the Zagros Region,Iran

Seismic strain and b value are used to quantify seismic potential in the Zagros region (Iran). Small b values (0.69 and 0.69) are related to large seismic moment rates (9.96×10¹⁷ and 4.12×10¹⁷) in southern zones of the Zagros, indicating more frequent large earthquakes. Medium to large b values (0.72 and 0.92) are related to small seismic moment rates (2.94×10¹⁶ and 6.80×10¹⁶) in middle zones of the Zagros, indicating less frequent large earthquakes. Small b value (0.64) is related to medium seismic moment rate (1.38×10¹⁷) in middle to northern zone of the Zagros, indicating frequent large earthquakes. Large b value (0.87) is related to large seismic moment rate (2.29×10¹⁷) in northwestern zone, indicating more frequent large earthquakes. Recurrence intervals of large earthquakes (M > 6) are short in southern (10 and 14 years) and northwestern (13 years) zones, while the recurrence intervals are long in the middle (46 and 114 years) and middle to northern (25 years) zones.     

Ground-roll attenuation using modified common-offset–common-reflection-surface stacking

We modified the common-offset–common-reflection-surface (COCRS) method to attenuate ground roll, the coherent noise typically generated by a low-velocity, low-frequency, and high-amplitude Rayleigh wave. The COCRS operator is based on hyperbolas, thus it fits events with hyperbolic traveltimes such as reflection events in prestack data. Conversely, ground roll is linear in the common-midpoint (CMP) and common-shot gathers and can be distinguished and attenuated by the COCRS operator. Thus, we search for the dip and curvature of the reflections in the common-shot gathers prior to the common-offset section. Because it is desirable to minimize the damage to the reflection amplitudes, we only stack the multicoverage data in the ground-roll areas. Searching the CS gathers before the CO section is another modification of the conventional COCRS stacking. We tested the proposed method using synthetic and real data sets from western Iran. The results of the ground-roll attenuation with the proposed method were compared with results of the f–k filtering and conventional COCRS stacking after f–k filtering. The results show that the proposed method attenuates the aliased and nonaliased ground roll better than the f–k filtering and conventional CRS stacking. However, the computation time was higher than other common methods such as f–k filtering.     

A priori models and inversion of gravity gradient data in hilly terrain

The increased popularity of airborne measurements of the gravity gradient tensor for resource studies and geological mapping has resulted in a new awareness of the importance of terrain effects. In these measurements, the terrain effect often overwhelms that of the underlying crust and it becomes important to formulate a strategy for taking it into account when presenting the data and when inverting the data into density models. Using newly acquired data from Northern Sweden, we first attempted to estimate a variable terrain density model by inverting the data using a terrain model with a laterally varying density. Using data weights related to the topography variations, we find the best estimate of the lateral variation of the terrain density. We translate this model into a full three-dimensional model such that all columns have the same vertical centre of mass as estimated from inspecting the radially averaged power spectrum of the area. This then defines a reference model for subsequent three-dimensional inversion of the gravity gradient tensor dataset. We tested this approach first on synthetic data calculated from the measured topography including two density anomalies before we applied it to the measured data. The result is a model in which the surface density variations are propagated downwards in a systematic manner now in better agreement with measured densities of rock samples in the area.     

Seismic hybrid simulation of a nonductile RC building with severe damage to multiple columns

Reinforced concrete frame structures built prior to the mid‐1970s are susceptible to brittle column failure under seismic action, potentially leading to progressive collapse of the structure. The behavior of columns susceptible to brittle shear‐axial failure has been studied previously but rarely has the interaction between damaged columns and the surrounding three‐dimensional structure been investigated experimentally and at full scale. In this study, as the second in a series of hybrid simulations, two full‐scale reinforced concrete columns of a representative pre‐1970s structure were tested at the Multi‐axial Full‐scale Substructure Testing and Simulation (MUST‐SIM) laboratory. Through the use of hybrid simulation, the interaction of the columns with the surrounding structure is studied under a severe seismic motion including vertical excitation. The computational model representing the remainder of the representative 10‐story structure is created in the computer program OpenSees. During the hybrid simulation, both physical specimens experience significant loss of shear and axial strength, and the effects of these failures on the surrounding system are described. The three‐dimensional computational model in OpenSees allowed for analytical flexural‐axial failure of a third column in the structure to occur. The effects of these multiple failures on the response of a full structural system under seismic action are quantified, and the progressive collapse resistance mechanisms are discussed. Copyright © 2016 John Wiley & Sons, Ltd.