Sandbox experiments are used to study frontal thrust fault spacing, which is a function of physical properties within the thrust wedge. We consider three styles of thrust progression in mono-vergent wedges: Style I, II and III. In Style I, frontal thrusts progress forelandward, maintaining a constant spacing, whereas Style II and Style III progression show increasing and decreasing spacing, respectively. The three styles are shown as a function of the following factors: basal friction (𝜇b), initial surface slope (𝛼) and basal slopes (𝛽), and surface erosion. For high 𝜇b (∼0.46), thrust progression occurs in Style II when 𝛼 > 2° and 𝛽 > 0.5°, and in Style III when 𝛼 and 𝛽 are high (𝛼 < 2° and 𝛽 < 0.5°). Style II transforms to Style I when the wedge undergoes syn-thrusting surface erosion. In contrast, low-basal friction (𝜇b = 0.36) gives rise to either Style I or III, depending on the magnitudes of 𝛼 and 𝛽. Conditions with 𝛼 = 𝛽 = 0 developed Style I, whereas Style III in conditions with any non-zero values of 𝛼 and 𝛽. In this case, surface erosion caused the process of thrust progression unsteady, and prompted outof-sequence thrusting in the wedge. This study finally presents an analysis of the three styles, taking into account the following two parameters: (1) instantaneous increase of hinterland thickness (𝛥 H2/He) and (2) forelandward gradient of wedge thickness (𝛿 H/𝛿x). Experimental data suggest that thrust sequences develop in Style II for low 𝛿 H/𝛿x and large 𝛿 He/He values and, in Style III as either 𝛿 H/𝛿x increases or 𝛥 He/He drops.
Volume 130, 2021
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