Gravitational and tectonic stress states within a deep-seated gravitational slope deformation near the seismogenic Periadriatic Line fault

Abstract

The role of tectonic horizontal stresses in activating deep-seated gravitational slope deformations (DSGSD) has rarely been studied. We applied a new numerical technique for determining the present-day stress states within a large DSGSD, situated near the Periadriatic Line fault (PAL) in the Eastern Alps. The stress states were calculated from three-dimensional displacements of the sinistral Obir fault conjugated to the dextral PAL fault, which also forms the upper DSGSD detachment plane. The analysed fault displacements occurred in two distinct activity phases associated with the elastic rebound along (i) the Obir fault in the summer of 2014, and (ii) the core of the PAL fault in the winter of 2014/2015. These periods were synchronous with the periods of increased local seismicity. The results brought an insight into a possible causative link between horizontal tectonic stresses and DSGSDs activation. We observed, that transient dextral transpressions and dextral transtensions opposing to the general fault kinematics associated to the elastic rebound had a potential to destabilize the DSGSD at the micrometre level. The applied stress-tensor calculation, although restricted only to shallow near-surface conditions, is a reliable method that can reveal stress states almost in the real-time.