The controls on when and how geological structures are produced by earthquake cycles

The comparison of geodetic, geomorphological, and geological observations shows a diverse range of mechanisms and timings of the growth of geological and topographic structures during earthquake cycles. I will describe examples from 8 locations in the Middle East and Asia, where observations of surface motions (using InSAR), geomorphology, and geology can be used to deduce what aspects of the geological structures are being produced by which components of earthquake cycles. In comparison to each other, these studies allow us to deduce the overall controls on the amount and style (e.g. folding or faulting) of off-fault deformation, and during which phase of the earthquake cycle these occur (i.e. co-seismic, post-seismic, or inter-seismic).

The local lithology plays an important role in controlling the nature of the earthquake cycles studied, and of the resulting geological structures. However, over many earthquake cycles the growth of these structures in turn affects the geometry of subsequent fault slip and off-fault deformation, leading to an overall evolution through time of the production of geological structures. Specifically, as mountain ranges grow and faulting steps into the adjacent basin, low-angle thrust faulting is associated with fold growth by co-seismic bedding-plane slip, and post-seismic (and in some cases inter-seismic) fault creep on steep ramps. In areas of mature faulting, with lithified rocks close to the surface, folding becomes less prevalent, and post-seismic fault creep concentrates on (sometimes multiple) structures close to the up-dip projection of the co-seismic fault plane. These observations allow us to establish the interplay between the evolution of geological structures and the nature of the earthquake cycles that produce them. By extension, these observations also allow us to establish the material properties that control the nature and timescales of the deformation.