An Attempt to Image Um El-Adam Cavity Structure in the Karst Terrain at Hit Area, Western Iraq

2020 ◽  
Vol 54 (1A) ◽  
pp. 44-54
Author(s):  
Ali Abed
Keyword(s):  
3D Model ◽  
3D Models ◽  
Electrode Spacing ◽  
Karst Terrain ◽  
Resistivity Imaging ◽  
Cavity Structure ◽  
2D Resistivity Imaging ◽  
2D And 3D ◽  
2D Resistivity

Um El-Adam cavity is one of the well-known cavities inside gypsum rocks in the Hit region, western Iraq, where this was chosen as a case study to evaluate 3D resistivity imaging technique detection and imaging of this type of cavity in complicated lithology. 3D view fulfilled by collating four 2D resistivity-imaging lines. The 2D resistivity imaging survey was carried out by Dipole-Dipole array with (n) factor and electrode spacing (a) of 6 and 2m, respectively. Both conventional inversion methods obtained the 2D and 3D models: standard least-squares and robust constrain options. The two options were able to define clearly the cave, but the second was more accurate, the dimensions of the cave in the inverse model closer to the actual dimensions. Horizontal slices displayed the final 3D model to reveal a 3D resistivity distribution with depth. The effect of Um El-Adam cavity appears after 1.5 m on the model slices, which is represented by increasing resistivity contrast compared to surrounding sediments. At the seventh and eighth slices, it was found that the size of the cavity exceeded compared with the actual dimensions. The results of this study indicated the high potential of this method for the detection and delineation of subterranean caves.

Optimisation of electrode arrays used in 2D resistivity imaging surveys

2007 ◽  
Vol 2007 (1) ◽  
pp. 1-4 ◽  
Author(s):  
M. H. Loke ◽  
Fouzan A. Alfouzan ◽  
M. N. M. Nawawi
Keyword(s):  
Electrode Arrays ◽  
Resistivity Imaging ◽  
2D Resistivity Imaging ◽  
2D Resistivity

Numerical modeling of seismically-induced slope displacements: a comparison between 2D and 3D finite difference models and Newmark-Displacements

2020 ◽  
Author(s):  
Gisela Domej ◽  
Céline Bourdeau
Keyword(s):  
Finite Difference ◽  
Cross Section ◽  
3D Model ◽  
3D Models ◽  
Southern Spain ◽  
Longitudinal Cross Section ◽  
Landslide Body ◽  
Mesh Grid ◽  
2D And 3D ◽  
2D Model

<p>The majority of numerical landslide models are designed in 2D. In particular, models based on finite difference methods (FDM) are time-consuming and – as a result – in most cases also cost-intensive. 3D models, therefore, increase the processing time significantly. Another contributing factor to long processing times in the context of modeling of seismically-induced displacements is the fact that mesh grid increments must be small due to the necessity of correct wave propagation through the material. The larger the frequency range of the applied seismic signal should be, the smaller has to be the mesh grid increment. 3D models are, however, considered as more realistic.</p><p>In this work, we present a comprehensive study on numerical 2D and 3D models of the Diezma Landslide, Southern Spain. The Landslide is represented in its shape as it appeared at the time of the main rupture on 18<sup>th</sup> of March in four model layouts: (1) a simplified model in 3D that outlines the landslide body with planar triangular tiles, (2) a longitudinal cross section through this simplified 3D model representing the simplified 2D model, (3) a smooth model in 3D that envelops the landslide body according to the main topographic features, and (4) a longitudinal cross section through this smooth 3D model representing the smooth 2D model.</p><p>On both the simplified and the smooth 2D models, a series of 11 seismic scenarios was applied as SV-waves assuming a source sufficiently far for vertical incidence at the model bottoms in order to produce horizontal shear inside the landslide body with respect to the underlying bedrock. All 11 signals are characterized by different frequency contents, Arias Intensities from 0.1 to 1 m/s, moment magnitudes from 5.0 to 7.0 and peak ground accelerations from 0.8 to 1.2 m/s², and therefore correspond to scenarios that represent the local seismicity in Southern Spain.<br>Because of time-related limitations, only four of these signals were respectively applied to the simplified and smooth 3D model. Newmark-Displacements were calculated using all 11 signals with the classic Newmark-Method that approximates the landslide body in 2D by a rigid block on an inclined plane, and with Newmark’s Empirical Law as spatial information covering the landslide area across the slope in regular intervals.</p><p>We present a systematic comparison of all models and obtained displacements, showing that the Newmark-Methods deliver very similar results to the maximum displacements obtained by FDM. Moreover, we discuss on a particular example that – although seeming more accurate in the layout – smooth models lead not necessarily to realistic results.</p>

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