Intraplate Seismogenic Tectonics in the Alpine Foreland

Lucie Novakova, Institute of Rock Structure and Mechanics, Academy of Science of the Czech Republic

Earthquake distribution in the lithosphere is rather uneven. Active plate boundaries, both convergent and divergent, generate majority of earthquakes. Despite the plate tectonics explains most earthquakes, quite a few earthquakes occur within plate interiors. In general, these, so called intraplate, earthquakes are less predictable. However, seismic hazard has to be established reliably before engineering constructions such as power plants, highways, tunnels etc. are even projected. Probabilistic assessment of seismic hazard provides only limited insight into intraplate seismic areas due to lack of data, mainly. Nevertheless within a plate interior occurred some of the strongest tremors ever recorded including New Madrid 1811 and 1812 events (Bolt, 1995). The intraplate seismicity is often bound to tectonic structures such as preexisting fault zones, failed rifts and suture zones. Unfortunately, intraplate seismogenic frameworks are usually less known in comparison with those on plate boundaries. To assess the seismic hazard within plate interior areas, it is therefore essential to study active capable intraplate faults and fault zones.

Compressional structures such as the Bohemian Massif are important in the Western and Central Europe tectonic framework. Within the Bohemian Massif, there are two main seismically active areas - west Bohemia with the Nový Kostel Fault Zone and east Bohemia with the Hronov-Poříčí Fault Zone (HPFZ). The HPFZ is a seismically active structure with documented earthquakes and swarms up to M4.7 (Kolínský et al., 2012). Field structural investigations, including fault-slip data collection were carried out on a number of natural outcrops and quarries with the aim of establishing a robust and field-constrained model for the local brittle structural evolution of the studied area. The kinematic frequent analysis was performed due to the distribution of the fault types in the orientations. Movements along the faults were categorized into different tectonic phases using the paleostress analysis. The paleostress analysis of the fault-slip data within the HPFZ resulted in identification of four tectonic phases during its tectonic development. Last but not least, intraplate stress was considered. Apparently, active tectonics in the area is being govern by the collision induced compression regime in the Alpine foreland.

Bolt, B.A., 1995. Intraplate seismicity and zonation. Bulletin of New Zealand national society for earthquake engineering, 29/4, 221-228.
Kolínský, P., Valenta, J., Gaždová, R., 2012. Seismicity, groundwater level variations and earth tides in the Hronov – Poříčí Fault Zone, Czech Republic. Acta Geodynamica et Geomaterialia, 9, 2, 166, 191-209.