Palaeoearthquakes in the Alps: New dating methods allow age determination about the Periadriatic Fault
Hanover/Jena. According to the current state of research, the eastern Periadriatic Fault System (PAF), on the border between the Eastern and Southern Alps, shows barely any historical and instrumental earthquakes – although it is one of the most important tectonic features of the Alps. In a new project, the Leibniz Institute for Applied Geophysics (LIAG) and the Friedrich Schiller University Jena are now using new dating methods, which for the first time will allow the most recent geological fault activities to be revealed.
By combining the dating methods „Optically Stimulated Luminescence“ (OSL) and „Electron Spin Resonance“ (ESR), the research period of palaeoearthquakes can be extended to a large part of the Quaternary period, i.e. to the most recent geological period in the Earth’s history (past 2.4 million years). For this period, little information on earthquakes in the eastern PAF is available yet. The research thus closes a crucial timescale gap in the knowledge of the history of the Alps between geological (>10 million year timescale) and instrumental/historical records (up to ~1000 years).
In order to fill this gap, numerous gouge samples are being taken and dated from fault lines along the eastern PAF system between South Tyrol, East Tyrol, Carinthia and Slovenia. Building on the fact that the intensity of the OSL and ESR signals in quartz and feldspar can be partially reset by frictional heating during seismogenic faulting, the scientists intend to better constrain the timing of past seismic events by investigating natural fault gouges along the eastern PAF system. This new approach will help to unravel which of these faults have been seismically active throughout the Quaternary. In this way, an understanding of tectonic movements in the transition zone of the Eastern and Southern Alps throughout the Quaternary period will be gained and a synthesized conceptual model of the deformation processes will be developed.
„The analyses should show for the first time which fracture segments of the eastern PAF system have shown seismic deformation throughout the entire Quaternary period“, explains Dr. Sumiko Tsukamoto, scientist at LIAG. “The overall goal is to characterize tectonic activity and to decipher whether it is concentrated along individual fault lines or in a broader zone.”
“To achieve this goal, we must be very accurate in the field during sampling as well as later in the laboratory when analyzing the samples“, says Prof. Dr. Kamil Ustaszewski, Friedrich Schiller University Jena. “Sampling requires precise structural-geological documentation of the spatial orientation and the composition of the rocks. These observations are the basis for a successful laboratory analysis and the interpretation of our results with regard to plate tectonic processes.“
The project is funded by the German Research Foundation (DFG), in the priority program „4D-MB – Mountain Formation Processes in 4 Dimensions“. It is also part of Working Group (WG) C „Active tectonics at the transition between the Alps and Dinarides“, which focuses on the only region of the Alps that is still tectonically active. The Priority Programme is a central part of the international AlpArray mission, which aims to map the structure of the European Alps from the surface to the mantle. Two other LIAG projects are also funded under the DFG priority programme: In one, four other main faults in the Alps will be dated, in the other, the focus lies on creating a geological profile along the new Brenner base tunnel.
In the appendix of the press release is a topographical map of the southeastern Alps with locations of important tectonic faults (black lines). Although it is an important tectonic lineament in the Alps, the Eastern Periadriatic Fault System (Line PG) shows much less earthquakes (red and grey dots) in comparison to the Eastern Southern Alps and the Northern Dinaric Mountains, both in historical and instrumental data.
Dr. Sumiko Tsukamoto
0511 643 2799
Friedrich Schiller University Jena
Prof. Dr. Kamil Ustaszewski
03641 948 623