Great challenges in structural geology and tectonics

Successful scientific theories provide theoretical understanding for reliable deterministic or probabilistic forecasting of events. In the past decades the volume of data obtained within the fields of structural geology and tectonics has increased enormously, but the theoretical understanding of the processes that generate these data has not advanced at the same rate. For example, after decades of research we still do not have successful theories explaining the size distribution of the Earth’s tectonic plates or the processes that form, drive, and destroy them. Subduction zones certainly contribute to these processes; yet we do not know how these zones initiate. While the largest earthquakes occur in subduction zones, much of the fault slip is aseismic (“creep”). We do not know the conditions that determine whether slip on a fault will be seismic or aseismic, or small or large. Similarly, with dense geodetic and seismic networks on many active volcanoes, we should be able to make a reliable forecast of the propagation path of an injected dyke— but normally we cannot. Dyke propagation and fault propagation depend on the energy available to drive these fractures. Our present knowledge of the energy budget of volcanic and seismic zones, however, is so limited that we cannot assess the maximum energies available for driving dyke-fed eruptions and earthquake faults. The topics listed here are among the great challenges in structural geology and tectonics. They all relate to the physics behind the observational data. Answering satisfactorily any of these challenges would constitute a major breakthrough in structural geology and tectonics.