Abstract Stress variations in the Earth's crust need to be understood in both the spatial and temporal domains to address a number of pressing societal issues. In this paper, precise three-dimensional records of fault kinematic behaviour obtained by mechanical extensometers are used to investigate changes in stress states along major faults in the Eastern Alps. The monitored faults are fractures with evident Upper Quaternary displacement and are directly attributed to their master tectonic structures. The results demonstrate that activity at the submillimetric scale is highly episodic; periods of repose are punctuated by conspicuous reactivation events affecting one or more of the displacement components. An original approach named the SMB2018 method is used to define the stress state associated with each fault reactivation event. The outputs evidence significant short-term changes in the local stress regime. The directions of the principal normal stresses calculated from these reactivation events present generally similar patterns for both compressional and extensional stress states. Consequently, submillimetric fault activity cannot be controlled by a rotating stress field; such shifts can only be caused by a change in the magnitude of the individual principal normal stresses so that the maximum compression changes to the minimum and vice versa.

Abstract During the current trend of the energy transition, many stratigraphic intervals that previously were thought as uneconomical from an oil and gas business perspective are being re-evaluated for low-carbon energy resource potential such as geothermal. This study presents a case study from the Vienna Basin, Austria, where the Early Badenian Rothneusiedl Formation has been targeted for a re-evaluation, utilizing existing sparse subsurface datasets of vintage quality. The historical cores were subjected to diverse analytical techniques covering sedimentological, petrophysical and thermophysical aspects. These analysis techniques provided the fundamental lithological characteristics and led to the creation of a synthetic conceptual sedimentological log, resultant selection of samples for further analyses, as well as the creation of gross depositional environment maps. The reservoir and thermal properties guided by the core-based lithofacies were required for evaluating the feasibility of the target strata. Overall, the limited and historical cores provided significant and robust data that proved crucial for assessing uncertainties and identifying sub-areas of the Vienna Basin for harnessing geothermal energy. This study demonstrates an important case example of the utilization of historical cores to their maximum potential and reiterates the value of core-derived data amongst digital technologies of the twenty-first century.