Structural Geology, Hydrogeology, Geophysics, Remote Sensing

• Structural geology


  The study of factors such as origin, occurrence, classification, type and effects of various secondary structures like folds, faults, joints, rock cleavage and are different from those primary structures such as bedding and vesicular structure, which develop in rocks at the time of their formation
• Outcrop


  Any geological formation exposed on the surface
• Strike


  The direction in which a geological structure is present. The strike direction may be defined as the direction of the trace of the intersection between the bedding plane

  
• Dip


  The slope or inclination of a geological structure. Dip is expressed both as direction and amount. The dip direction is the direction along which the inclination of the bedding plane occurs

  
• Slickenside


  A fault plane
• Fold


  A bend in a set of horizontal layers that are subjected to compressive forces, either upward or downward
• Folds


  • They may occur as single local bends or may occur repeatedly and intricately folded to the tectonic history of the region
• Basis for classification of folds

  • Symmetrical character
  • Upward or downward bend
  • Occurrence of plunge
  • Uniformity of bed thickness
  • Behavior of the fold pattern with depth
• Anticline


  A fold where the beds are bent upwards, resulting in a convex upwards structure with the older beds towards the concave side
• Syncline


  A fold where the beds are bent downwards, resulting in a convex downwards structure with the younger beds towards the concave side
• Symmetrical fold


  A fold where the axial plane divides it into two equal halves that are mirror images

  
• Asymmetrical fold


  A fold where the compressive forces responsible are not of the same magnitude, resulting in unequal halves
• Plunging fold


  A fold where the fold axis is inclined to the horizontal plane
• Non-plunging fold


  A fold where the fold axis is horizontal
• Open fold


  A fold where the bed thickness is uniform throughout
• Closed fold


  A fold where the beds are thinner in the limb portions and thicker at the crest and trough
• Similar fold


  A fold where the shape or pattern remains the same at depth
• Parallel fold


  A fold where the crest and trough become pointed or rounded with depth
• Overturned fold


  A fold where one of the limbs is overturned, resulting in the beds being in reverse order
• Chevron fold


  A fold with sharply bent, angular crest and troughs
• Isoclinal fold


  A fold where the limbs are mutually parallel to a great extent
• Fan fold


  A fold where the limbs of anticlines dip towards each other and the limbs of synclines dip away from each other, resulting in a fan-like shape
• Dome


  A fold where the beds are locally pushed up, with dips in all directions from a common central top point
• Basin


  A fold where the beds are locally pushed down, with slopes in all directions towards a central point
• Geanticline


  A very large-scale anticline
• Geosyncline


  A very large-scale syncline
• Drag fold


  A minor asymmetrical fold within a major fold, confined to incompetent beds sandwiched between competent formations, due to shearing/dragging effect
• Mechanisms of folding


  1. Slips or shear occur between beds, similar to slipping of cards when folded

  2. Thinning of limbs and thickening of crest and trough, common in weak and incompetent rocks like shales
• From the Civil engineering point of view, faults are the most
• Fractures


  • Crest portions are eroded quickly leading to conspicuous degradations locally
• Trough portion


  • Highly compressed and hence offer a greater resistance to erosion, stand out in the long run at a greater elevation, while the adjacent parts degrade fast
• Anticlinal valleys


  Change over to valleys
• Anticlinal hills

  Change over to hills
• Parallel folds


  • Orthogonal thickness is same all around the fold
  • Thickness is same parallel to the axial plane of the fold
  • Outer and inner arc have same curvature
  • Dip isogons are parallel to each other
• Faults


  • From the Civil engineering point of view, faults are the most unfavorable and undesirable geological structures at the site for any given purpose
  • Faults considerably weaken the rocks and render the sites in which they occur as unfavorable places for all constructional purposes
  • As long as the faults are active, the site is unstable and susceptible to upward, downward or sideward movement along the fault plane, thereby making the places highly hazardous for foundation purposes
• Faults


  Structurally, faults may be described as fractures along which relative displacement of adjacent blocks has taken place
• Joints


  Fractures in rocks where relative displacement of adjacent blocks has not taken place
• Magnitude of Faults


  • Some occur for short distance, while others can be traced for very long distances
  • Displacement may be less than a centimeter while in other it may be many or even kilometers
  • Magnitude of faulting depends on the intensity and the nature of shearing stresses involved
• Fault Plane


  • Rarely the displacement during faulting occurs along a single fault plane, often along a number of parallel fractures
  • Fault plane may be plain or straight or may be curved or irregular, it may be horizontal or inclined or vertical

  
• Faulting occurs when shearing resistance of the geological formation is overcome by the tectonics forces, often accompanied by earthquakes and an indication of subsurface instability