Training the creation, visualisation and interpretation of fault maps for the subsurface – using tectonic geomorphology

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.