Seismic analysis of semi-sine shaped alluvial hills above subsurface circular cavity

In this study, a seismic analysis of semi-sine shaped alluvial hills above a circular underground cavity subjected to propagating oblique SH-waves using the half-plane time domain boundary element method (BEM) was carried out. By dividing the problem into a pitted half-plane and an upper closed domain as an alluvial hill and applying continuity/boundary conditions at the interface, coupled equations were constructed and ultimately, the problem was solved step-by-step in the time domain to obtain the boundary values. After solving some verification examples, a semi-sine shaped alluvial hill located on an underground circular cavity was successfully analyzed to determine the amplification ratio of the hill surface. For sensitivity analysis, the effects of the impedance factor and shape ratio of the hill were also considered. The ground surface responses are illustrated as three-dimensional graphs in the time and frequency domains. The results show that the material properties of the hill and their heterogeneity with the underlying half-space had a significant effect on the surface response.

     

Combining process-based and surface-based models to simulate subsurface heterogeneity in volcanic aquifers

Realistic models of lithologic structure are critical for predicting flow and transport through heterogeneous volcanic aquifers. Existing models of lava flows based on physical processes are able to realistically simulate flow geometry and lithology, but the computational intensity limits applicability in generating entire aquifers. Fast surface-based models have been developed for hazard mapping, but these do not incorporate 3D geometry or lithology critical for hydrogeologic applications. Here we develop a hybrid modeling method (HMM) based on a combination of a process-based model (PBM) and a surface-based model. The methodologies are presented and compared to a known single flow and to each other in a full aquifer simulation. Results indicate that both the PBM and HMM simulations reasonably reproduce the flow geometry (length, branching, thickness) of the 1984 eruption of Mauna Loa in Hawai’i. Simulations of a volcanic aquifer built from 100 flows with the PBM and HMM are similar in spatial distribution and overall proportions of lithology (aa, transitional, pahoehoe, ash), flow geometry, and aquifer geometry. Thus, the hybrid method is an efficient method to generate geologically realistic models of volcanic aquifer structure. Model realism and parameterization can be improved as more field data become available.     

Implementation of a hybrid MLP-FFA model for water level prediction of Lake Egirdir,Turkey

The predictive ability of a hybrid model integrating the Firefly Algorithm (FFA), as a heuristic optimization tool with the Multilayer Perceptron (MLP-FFA) algorithm for the prediction of water level in Lake Egirdir, Turkey, is investigated. The accuracy of the hybrid MLP-FFA model is then evaluated against the standalone MLP-based model developed with the Levenberg–Marquadt optimization scheme applied for in the backpropagation-based learning process. To develop and investigate the veracity of the proposed hybrid MLP-FFA model, monthly time scale water level data for 56 years (1961–2016) are applied to train and test the hybrid model. The input combinations of the standalone and the hybrid predictive models are determined in accordance with the Average Mutual Information computed from the historical water level (training) data; generating four statistically significant lagged combinations of historical data to be adopted for the 1-month forecasting of lake water level. The proposed hybrid MLP-FFA model is evaluated with statistical score metrics: Nash–Sutcliffe efficiency, root mean square and mean absolute error, Wilmott’s Index and Taylor diagram developed in the testing phase. The analysis of the results showed that the hybrid MLP–FFA4 model (where 4 months of lagged combinations of lake water level data are utilized) performed more accurately than the standalone MLP4 model. For the fully optimized hybrid (MLP-FFA4) model evaluated in the testing phase, the Willmott’s Index was approximately 0.999 relative to 0.988 (MLP 4) and the root mean square error was approximately 0.029 m and compared to 0.102 m. Moreover, the inter-comparison of the forecasted and the observed data with various other performance metrics (including the Taylor diagram) verified the robustness of the proposed hybrid MLP-FFA4 model over the standalone MLP4 model applied in the problem of forecasting lake water level prediction in the current semi-arid region in Turkey.     

Predicting seismic permanent displacement of soil walls under surcharge based on limit analysis approach

Seismic permanent displacement of the soil walls plays an important role in design of these structures. Due to the increase in growth of urban areas and the limitations in use of flat grounds, many structures are built near slopes and retaining walls. During earthquakes, these structures can apply an additional surcharge on the wall. The intensity and location of the surcharge is of considerable importance on the seismic displacements of the soil wall. In this study, by using the limit analysis and upper bound theorem, seismic permanent displacement of the soil wall under surcharge has been analyzed. Thus, a formulation is presented for calculating the yield acceleration and seismic displacement for different surcharge conditions. The effect of seismic acceleration, surcharge intensity, its location and soil properties is investigated. A parameter called the “displacement coefficient” is proposed, and is a potential modification for Newmark’s sliding-block method.     

Nonlinear modeling of cyclic response of RC beam–column joints reinforced by plain bars

Experience of previous earthquakes shows that a considerable portion of buildings reinforced with plain bars sustain relatively large damages especially at the beam–column joints where the damages are mostly caused by either diagonal shear cracks or intersectional cracks caused by bar slippage. While previous works mainly focus on shear failure mode, in this study, the emphasis is placed on slip based cracks as the dominant failure mode. A systematic procedure is introduced to predict the dominant failure mode at the joint which is based on the dimensional properties, reinforcement details, and axial and shear load at the joint. In addition, a relatively simple and efficient nonlinear model is proposed to simulate pre- and post-elastic behavior of the joints which fail under bar slippage mode. In this model, beam and column components are represented by linear elastic elements, dimensions of the joint panel are defined by rigid elements, and effect of slip is taken into account by a nonlinear rotational spring at the end of the beam. The proposed method is validated by experimental results for both internal and external joints .     

New magnitude scaling relations for earthquake early warning in the Alborz region,Iran

Rapid magnitude estimation relations for earthquake early warning systems in the Alborz region have been developed based on the initial first seconds of the P-wave arrival. For this purpose, a total of 717 accelerograms recorded by the Building and Housing Research Center in the Alborz region with the magnitude (M_w) range of 4.8–6.5 in the period between 1995 and 2013 were employed. Average ground motion period (\( \tau_{\text{c}} \)) and peak displacement (\( P_{\text{d}} \)) in different time windows from the P-wave arrival were calculated, and their relation with magnitude was examined. Four earthquakes that were excluded from the analysis process were used to validate the results, and the estimated magnitudes were found to be in good agreement with the observed ones. The results show that using the proposed relations for the Alborz region, earthquake magnitude could be estimated with acceptable accuracy even after 1 s of the P-wave arrival.     

Identification of Nutrients Critical Source Areas with SWAT Model under Limited Data Condition

Water Resources - The lack of long term observed data is the main challenge in many simulation-based studies for identification of nutrient critical source areas (CSAs). This study explored the...     

Sedimentological and petrochemical studies of Jurassic clastic rocks,Habo Dome Basin,Kachchh Mainland,Northwest India: Implications for depositional environment,provenance, and tectonic setting

Mesozoic rocks are extensively and excellently preserved in the western Indian shield in several basins. The Kachchh Mainland Basin (KMB), comprising six small sub‐basins, is the main repository of these sediments. Habo Dome Basin, situated in the easternmost part of KMB and largest among the six basins, hosts clastics of the Chari Formation of Jurassic age. The fluctuating transgressive–regressive facies cycle, developed during the Callovian and Late Early Oxfordian in the Habo Dome Basin, was mainly controlled by local tectonics and not by global eustatic fluctuations. Near magmatic relationships are displayed by various elements of the clastic rocks of Habo Dome Basin. Two litho‐chemical groups have been identified in Habo Dome Basin, which are cyclically repeated over entire lithostratigraphic sequence, indicating alternate pulses of sediment inputs from two different sources under palpitating tectonic conditions. Provenance indicator elements and their ratios coupled with source modeling indicate predominantly felsic source with basic and alkalic components. Integrated analysis of petrograhic and geochemical characteristics suggests two source terranes for these rocks: a granitoid source with significant basic volcanics (Banded Gneissic Complex) and a granite–gneissic source with minor alkaline volcanics (Nagarparkar Massif) lying to northeast and NNW respectively. The petrochemistry of Habo Dome clastics suggests their deposition in a fault controlled sink which was influenced by sea level changes. Drifting of the Indian plate resulted in the opening of series of rifted basins in the Kachchh Mainland during Late Triassic/Early Jurassic, which were closed later during collision of Indian plate with Eurasia at early Eocene. The Habo Dome Basin which opened up as a half graben in response to the initial stress regime, remained tectonically unstable until the cessation of pre and post collisional stress regimes.     

Climate change impact on Caspian Sea wave conditions in the Noshahr Port

Excessive usage of fossil fuels and high emission of greenhouse gases have increased the earth’s temperature and consequently have led to changes in wind and wave regimes. The main effects of climate change on oceans are warming of the ocean water, melting of ice, acidification of ocean water, and change in the ocean currents. The main effects of climate change on coastal regions are change in the coast hydrodynamics, sea level rise, change in wave height, coastal erosion, coastal structure damage, food shortage, and storms. Due to the importance of waves in the coastal zone and its effect on erosion and sedimentation, it is necessary to study wave changes. In this study, the effect of climate change on wave specifications was evaluated in the southern coast of the Caspian Sea in Noshahr Port. To simulate wave parameters, the third generation spectral Simulating WAves Nearshore (SWAN) model was used. Wave modeling was carried out using the SWAN numerical model for two 30-yearly periods, including the control period (1984 to 2014) and the future period (2051 to 2080). For wave modeling in the control period, the European Center for Average Weather Forecast wind field was used, and for the future period, a downscaled wind field from Coordinated Regional Downscaling Experiment projection, which was sponsored by World Climate Research Programme, based on the most recent emission scenarios RCP2.6, RCP4.5, and RCP8.5, was used. The model results were calibrated and verified with buoy-recorded data. The effect of the climate change on the wave parameters was evaluated by studying the differences between the patterns in three scenarios and the control period. Results showed that the 30-year maximum significant wave height will increase because of climate change, and the wave direction will not change. In addition, the intensity of storms will increase in the future.

     

Rehabilitation of earthquake damaged external RC beam‐column joints by joint enlargement using prestressed steel angles

The effectiveness of a rehabilitation method based on joint enlargement using prestressed steel angles to enhance the seismic behavior of damaged external reinforced concrete beam‐column joints was experimentally investigated. Three half‐scale joints having either non‐seismic or seismic reinforcement details were tested both before and after rehabilitation by applying lateral cyclic loading of increasing amplitudes. Two defects were considered for the two non‐seismic units, being the absence of transverse steel hoops and insufficient bond capacity of beam bottom steel reinforcing bars in the joint panel zone. The damaged specimens were rehabilitated by injecting epoxy grout into existing cracks and installing stiffened steel angles at the re‐entrant corners of the beam‐column joint, both above and below the beam, that were mounted and held in place using prestressed high‐tensile strength bars. The test results indicated that the seismic performance of the rehabilitated specimens in terms of strength, stiffness, and ductility was fully recovered and comparable with the performance of the seismically detailed specimen. Copyright © 2016 John Wiley & Sons, Ltd.