Present-day kinematic behaviour of active faults in the Eastern Alps

The Neogene to Quaternary lateral extrusion of the Eastern Alps towards the Pannonian Basin is accommodated by a system of strike-slip faults. Despite decades-lasting GPS observations, no information on contemporary kinematic behaviour of these faults has been available. Therefore, we had monitored subsidiary and/or conjugated faults associated to these major fault systems in six caves throughout the Eastern Alps over a 1.5-2.5-year observation period by means of high-resolution three-dimensional Moire extensometers TM71. We confirmed that the monitored faults revealed present-day aseismic displacements at a micrometer level during several activity phases that usually also coincided with periods of increased local seismicity. The annual displacement rates of the monitored faults were mostly about an order of magnitude smaller than the rates of the entire crustal wedges revealed from GNSS. The particular displacements consisted of a variety mechanisms and faulting regimes. Fault dilations and compressions were mostly associated with thermal-volumetric variations, normal dip-slips and downward hanging-wall displacements originated due to gravitational relaxation or mass movement. Displacements with the same mechanisms as the geologically documented fault systems or with an upward component were attributed to tectonic creep and strain built-up during the interseismic period. On the other hand, the countervailing displacements opposite to the master fault kinematics were most probably caused by elastic rebound. They were usually registered few days in advance to distinct local earthquakes that were simultaneously activated at locked segments within the same deformation band. Therefore, the countervailing events could be considered an indicator of impending near earthquake within the rebound zone; their better understanding and real-time detecting could be a step forward to an effective earthquake early warning in similar geological settings.