Abstract Intruding magma can create space by uplift and elastic bending of the overburden, which locally fractures the deforming volume and produces flat-topped or dome-like forced folds. Here, I map such fracture networks and quantify their geometry and connectivity across a range of natural and modelled intrusion-induced forced folds. I show that there is a positive relationship between forced fold length and amplitude, and all fracture networks comprise traces, with variable lengths and orientations, that are more intense and denser where fold curvature is greatest. Fracture length populations are typically best described by power-law distributions, but some fit better to log-normal or exponential distributions. Connectivity of fracture networks is low and generally increases with folding, but resurfacing by eruptive products can disrupt this trend. My work supports previous analyses of forced folds and fractures, suggesting that we can use the fracture characteristics of exposed forced folds to predict that of buried forced folds. Due to their geometry and fracture network, intrusion-induced forced folds make ideal fluid traps. As these forced folds are common in many volcanic settings and sedimentary basins, we should consider their potential as exploration targets for water, magmatic-related mineral and metal deposits, and particularly CO 2 storage.

Abstract Fault mapping is essential for understanding subsurface geological structure. However, effective training of students in developing and understanding fault patterns in 3D seismic imagery is impeded by the time-investment needed to acquire competence using software and then creating depth-structure maps of stratal horizons. Here an exercise is laid out that can achieve the desired experience – using the young fault systems of Afar (Djibouti), where former land-surface-defining basalt flows are offset by arrays of normal faults. The top-basalt surface, displayed on GoogleEarth, is in effect a depth-structure map and the gaps (‘fault-loss’) in this surface approximate to exposed fault surfaces. The mapping exercise is described and illustrated here step-wise. The fault system is gradually mapped out to reveal examples of long-continuous faults, branching patterns, relaying faults and isolated fault segments. Alternative criteria for identifying faults can be examined, with analogies in seismic interpretation. This can inform discussion of the approaches and uncertainties inherent in mapping faults in the subsurface. The study may be extended to consider the pattern of early–syn-rift depositional systems. Collectively these tasks can be progressed within an hour or so, providing effective insights into the structure of normal fault systems that cannot be replicated by conventional fieldwork.