Fig. 5. Images for C1 and fracture surfaces (a) overall view, the dashed rectangle indicates the prospective cut sections, (b) the cut sections above and below the C1, named C1-A and C1-B respectively, (c, d) overall fracture surface of C1-A and C1-B respectively, a red dashed circle is the likely origin and beach marks are shown, (e, f) zoomed-in view of clear beach marks for the dashed triangular region in (c and d) they appear to originate from the same point, (g, h) beach marks outside the dashed triangular region