Fig. 4: Ground-penetrating radar (GPR) profiles of the Joerg Peninsula (JP) suture zone.

See Fig. 2 for profile locations and directions. a Profile across the suture zone. b Profile along the suture zone. In both a and b, the main observations are labelled, including (Type A) layered horizontal reflections from the ice-shelf surface to depths of ~140 m that exhibit buckling within the suture zone, where four prominent buckle stacks are indicated by the four black arrows in a; (Type B) events between depths of ~140 and ~220 m that appear as scattered hyperbolae or locally continuous reflections, respectively, in a and b; (Type C) events deeper than ~220 m that have distorted or disrupted hyperbolic shapes; and (Type D) reflections from the ice-shelf base. c Interpreted profile across the suture zone. d Interpreted profile along the suture zone. The solid red lines in c and d mark the total seismic profile lengths at JP-Seis and SI-Seis at the ice surface and at depth also mark the top of the basal marine ice (‘Top’) and the ice-shelf base (‘Base’), as delineated, respectively, by our GPR and seismic data. The depths of the bases of the mélange and basal marine ice units are unknown, as indicated by the black question marks. In both c and d, the three main layers considered by our flowline model (FLM) are labelled, including a surface layer (FLM-1) integrating accumulated firn (ISU-1) and meteoric ice (ISU-2), a central layer (FLM-2) integrating advected glacier ice (ISU-3) and mélange (ISU-4) and a basal layer of accreted marine ice (FLM-3, equivalent to the ISU-5) (Fig. 5). Also labelled in both c and d are the three main layers considered by our viscous buckling model (VBM), including two soft layers—firn (VBM1, equivalent to ISU-1) and the conglomerate layer (VBM3) of mélange (ISU-4), basal marine ice (ISU-5) and meteoric ice blocks (ISU-3)—that enclose the hard layer of in situ meteoric ice (VBM2, equivalent to ISU-2).