Identification of pulse-like ground motions using artificial neural network

For more than 20 years, the concept of near-fault pulse-like ground motion has been a topic of great interest due to its distinct characteristics, particularly due to directivity or fling effects, which are hugely influenced by the rupture mechanism. These unexpected characteristics, along with their effective frequency, energy rate, and damage indices, create a near-fault, pulse-like ground motion capable of causing severe damage to structures. One of the most common approaches for identifying ...     

Investigation on the Local Scour Beneath Piggyback Pipelines Under Clear-Water Conditions

A piggyback pipeline consists of two pipes such that the secondary line rides on the main pipe with a fixed distance between two pipes in length. The novel strategy is utilized in offshore areas instead of a single flow line. In this regard, there are only a handful of experimental and numerical studies investigating the effect of scour below a piggyback pipeline under steady current. Hence, this study focuses on examining the influential factors on scouring due to steady current including the pipe diameter and the gap between pipes through numerical simulations and experimental tests. Accordingly, at the first phase of the research, a single pipe was established and tested in laboratory to compare the results with those of an empirical equation. After finishing experimental verifications,piggyback pipelines were also assembled to study the scouring under steady current conditions. It was concluded that by increasing the gap distance between the pipes, the maximum scour depth decreases; however, an increase in the small pipe's diameter results in a larger maximum scour depth. Secondly, numerical simulations were carried out using the FLOW-3D software which was found to be a suitable tool for the numerical investigation of this study.Finally, the numerical results have been compared with the corresponding experimental data and a relatively good agreement was achieved between them.     

Spatial analysis of monthly precipitation in Turkey

Summary  The principal objectives of this paper are to develop and validate an optimum interpolation method for the spatial analysis of monthly precipitation in Turkey. A two-dimensional optimum interpolation objective analysis scheme has been developed for the spatial analysis of precipitation. The model is developed for generating statistically optimum interpolation based on the irregular distribution of meteorological stations. One question that affects the optimum interpolation method and, indeed, all such techniques, is how many observations should be allowed to influence a given grid point? The method developed in this paper addresses this question. For the implementation of the method, 52 stations are considered for Turkey, with 30 years of monthly data at each point. It is observed that each monthly average spatial correlation function shows a monotonically decreasing pattern based on 15 km interval averages. The method provides high estimation accuracy in dense station locations such as in northwestern Turkey. Precipitation contour maps obtained by the optimum interpolation method indicate two spatial trends over Turkey which have not been identified in any previous study. Received June 24, 1999/Revised April 26, 2000     

Runoff and sediment yield modeling using SWAT model: case of Wadi Hatab basin,central Tunisia

This study presents an application of the model Soil and Water Assessment Tool (SWAT) to simulate daily and monthly water flow and sediment fluxes in the Wadi Hatab watershed (2200 km²) located in central Tunisia. The study basin is characterized by a significant climatic contrast, abrupt topography, and soil fragility, resulting thereby in flash floods and important water erosion rates. This alarming situation requires urgent interventions in order to preserve water and soil resources, implying the need for a decision tool for proper integrated management of the watershed. The model was calibrated and validated based on a comparison of simulated and observed flow rates at the basin outlet (hydrometric station Khanguet Zazia), during the periods 1987–1988 and 1989–1990, respectively. The comparison was based not only on visual inspection of the agreement between observed and simulated time series, but also on statistical parameters. Indeed, for the daily time step application, the Nash—Sutcliffe efficiency (NSE) values were 0.52 and 0.61, and the coefficient of determination (R²) was 0.54 and 0.61 for calibration and validation, respectively. As for the monthly time-step application, the obtained NSE values were 0.67 and 0.89 while R² values were 0.83 and 0.87 for calibration and validation, respectively. This clearly shows the reasonably good agreement between simulated and observed flow rates. In terms of erosion, the model gave sediment yield values ??of 1.15 and 5.37 t/ha/year during the periods of calibration and validation, respectively.     

New data on the Vrancea Nappe (Moldavidian Basin, Outer Carpathian Domain, Romania): paleogeographic and geodynamic reconstructions

A study has been performed on the Cretaceous to Early Miocene succession of the Vrancea Nappe (Outer Carpathians, Romania), based on field reconstruction of the stratigraphic record, mineralogical-petrographic and geochemical analyses. Extra-basinal clastic supply and intra-basinal autochthonous deposits have been differentiated, appearing laterally inter-fingered and/or interbedded. The main clastic petrofacies consist of calcarenites, sub-litharenites, quartzarenites, sub-arkoses, and polygenic conglomerates derived from extra-basinal margins. An alternate internal and external provenance of the different supplies is the result of the paleogeographic re-organization of the basin/margins system due to tectonic activation and exhumation of rising areas. The intra-basinal deposits consist of black shales and siliceous sediments (silexites and cherty beds), evidencing major environmental changes in the Moldavidian Basin. Organic-matter-rich black shales were deposited during anoxic episodes related to sediment starvation and high nutrient influx due to paleogeographic isolation of the basin caused by plate drifting. The black shales display relatively high contents in sub-mature to mature, Type II lipidic organic matter (good oil and gas-prone source rocks) constituting a potentially active petroleum system. The intra-basinal siliceous sediments are related to oxic pelagic or hemipelagic environments under tectonic quiescence conditions although its increase in the Oligocene part of the succession can be correlated with volcanic supplies. The integration of all the data in the “progressive reorientation of convergence direction” Carpathian model, and their consideration in the framework of a foreland basin, led to propose some constrains on the paleogeographic-geodynamic evolutionary model of the Moldavidian Basin from the Late Cretaceous to the Burdigalian.     

A Middle Jurassic sauropod tracksite in the Argana Basin,Western High Atlas,Morocco: an example of paleoichnological heritage for sustainable geotourism

A Middle Jurassic site at Tafaytour area (Argana Basin, Morocco) with trackways of six large sauropod dinosaurs is regarded as having high scientific and touristic value. The new dinosaur track site is extremely vulnerable, and suffers from continuous degradation caused by weathering and human activity. Documentation and protection of this tracksite is still a necessity for its integration into local geotourism activities, where it may have a socio-economic impact on the local population. Taking into consideration many similar tracksites, and strata of great paleontological interest in Morocco, including the Tafaytour tracksite, the implementation of legislation for the protection of Morocco's geological heritage, especially the paleoichnological heritage, to protect against destruction, is strongly recommended. This is necessary to cement geoheritage impact, both for scientific reasons and to value add to the socio-economic activities of the local people.     

Helical Eruptive Prominence Associated with a Pair of Overlapping CMEs on 21 April 2001

The eruption of limb prominence on 21 April 2001 associated with two coronal mass ejections (CMEs) is investigated. Hα images reveal two large-scale eruptions (a prominence body and a southern foot-point arch), both showing helical internal structure. These two eruptions are found to be spatially and temporally associated with the corresponding CMEs. The kinematics and the study of geometrical parameters of the prominence show that the eruption was quite impulsive (with peak acceleration ≈470 m s⁻²) and has taken place for relatively low pitch angle of helical threads, not exceeding tan θ≈1.2. The stability criteria of the prominence are revisited in the light of the model of Vršnak (1990, Solar Phys. 129, 295) and the analysis shows that the eruption violates the instability criteria of that model. Finally, the energy stored in the prominence circuit and the energies (kinetic, potential, and magnetic) of the associated CMEs are estimated and it is found that there was enough energy stored in the prominence to drive the two CMEs. S.S. Ali is on leave from Aligarh Muslim University, Aligarh, 202 002, India.