Data from depth to surface to define the 3D anatomy of an active fault-propagation fold: a key example from the western Caucasus (Georgia)

Abstract

In the present work we showcase a multidisciplinary study aimed at defining the ongoing deformation processes due to fault propagation and folding at the Tsaishi fold, western Caucasus (Georgia).Our approach consists in the integration of geomorphological observations, field geological-structural data and seismic reflection sections, allowing us to reconstruct a 3D model of this active fold, from depth to surface.The Tsaishi fold is an anticline located at the southwestern tip of the Rioni Basin uplifted area, at the foothill of the Greater Caucasus. The folding process that has been recognized started at the beginning of the Middle Miocene, although preliminary data suggest the possibility of an initial local uplift in the Oligocene. Considering field observations, we suggest that the folding process continues nowadays, giving rise to a south-verging anticline, as shown by upwarped late Quaternary river deposits.Integrating seismic reflection sections and field observations, we show that the fold backlimb is affected by three main back-thrusts, whereas, based on seismic sections, at the foot of the forelimb a main north-dipping thrust is very close to the surface. Where the thrust reaches the surface, we recognized the presence of a 13-km-long fault scarp (or fold scarp), where historical seismological data locate the epicenter of the strongest earthquake of the area, with Ms 6.0, the so-called Tsaishi earthquake of 1614 CE.