MECHANICAL DISCONTINUITY AND ITS IMPLICATION IN THE MORPHOLOGY OF IMPACT CRATER: AN EXPERIMENTAL INVESTIGATION

Impact craters have two types of shapes in plan view: (i) circular (or elliptical) shape and (ii) polygonal shape. The present work has been carried out with analogue models to understand the controlling parameters that lead to the varied morphology of impact crater. Though the size and shape of the impactor is important for crater morphology, our experimental results point out the significance of mechanical discontinuity, such as pre-existing fractures or joints planes in the target rock in shaping the crater morphology.

For example, experiments with homogeneous and isotropic target material produced circular impact craters (CICs). However, polygonal impact craters (PICs) mostly develop with pre-impact mechanical discontinuity within the target material. Circular crater is characterized by circular and radial fractures. In contrast, circular fractures are replaced by straight segment of the crater rim in polygonal impact crater. Experimental results show that presence of discontinuity in the target rock develop straight segments either at moderate to high angle with the pre-existing zone of discontinuity or parallel to it giving rise to PIC. Moreover, radial fractures become insignificant in the case of PICs. Also, the depth/diameter ratios of the impact craters are seen to increase with the presence of discontinuity in the target material. This set of experiments suggests that the pre-existing fracture or discontinuity zone of the target control the geometry of the impact fracture formation and thus the straight segments of the PICs can be compared with major structural lineaments or preexisting fracture network of the area.