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DEM: Thrusts 3. The effect of the height of pre-existing basement structures on faulting

media
posted on 11.05.2022, 13:47 by Emma FinchEmma Finch

Application of a Discrete Element Model to investigate the effects of the pre-kinematic strength on thrusting when basement structures are present. 

The media in these experiments contain 20664 elements in a box that is 300 x 30 units. Elements are distributed randomly with radii of 0.5, 0.4. 0.3 and 0.2 units. The left-hand boundary is incremented to the right at 0.00005 unit/timestep to a total compression of 150 units (50%). The experiments run for 3 million timesteps with outputs every 50,000 which are presented in the movies. The media is divided into 14 layers. Colours indicate the ‘strength’ of the media where numbers in the file name represent the separation between elements as a function of their initial separation that is required for bonds to break. This is distinct for each bond pair where each element is assigned a breaking separation determined from the average of the strength assigned to each element. 

Experiments are performed with two basement structures representing normal faults dipping towards the compression direction. The height of both faults is 15 units, half of the pre-kinematic media and they dip at 50o towards the left. The initial position of the faults remains fixed at 150 and 225 units.

The movies show the results from experiments where the pre-kinematic layers are:

  • the same strength (F_0.0*_onf),
  • the upper seven layers are relatively stronger (Hu_0.0*_onf), 
  • the lower seven layers are relatively stronger (Hl_0.0*_onf),
  • alternating layer strength between weak (1x, 0.01, grey/black layers) and more competent layers which are represented by layers that are white and (a) purple (2x), (b) blue (4x), (c) green (6x) and (d) orange (8x).

The filename shows the strength of the material relative to 1x (F_0.01_onf.gif, grey) . The *_compare movies show three representations of fault evolution. 

  • The upper image shows the bonds between elements as they break where the darker the colour, the more bonds are broken with initial neighbours.
  • The central image is the layers in the experiment.
  • The lower image shows a coherence plot where an element is coloured relative to the difference between its layer number and that of the element immediately below it. Elements within layers are white and  fault locations are highlighted as the colour darkens.

A presentation of final results of the experiments and their associated filenames are in DEM_Thrusts 3.pdf.The methodology can be found in the first reference below. The second links to experiments with single layer strength and the third to those with alternating layer strength for comparison.

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