SEISMIC SLIP AND ASEISMIC CREEP ON MAJOR FAULT SYSTEMS OF THE EASTERN ALPS RECORDED IN SHEARED FLOWSTONES

One of the dominant neotectonic processes in the Eastern Alps involves the Neogene and Quaternary lateral extrusion towards the Pannonian Basin. It involves gravitational collapse and tectonic escape, coeval with north-south shortening between the Adriatic and European plates. In the Eastern Alps, the 300 km long SEMP (Salzach-Ennstal-Mariazeller-Puchberger) fault accommodated a sinistral displacement of about 60 km during Tertiary time, but presently the Mur-Muerz sinistral fault is the most seismically active, with 2 mm per year slip according to the GPS data. Although recent earthquakes and GPS records prove the activity of the faults, geological evidences on the surface are rare. However, tectonically displaced cave passages and damaged speleothems in the caves of the Eastern Alps are reported to capture the past and present activity along the SEMP and Mur-Muerz faults. Here, we examine the microstructural characteristics of sheared calcite flowstone that speak to mechanics of the fault friction in shallow parts of the SEMP fault. Samples with variety of deformational mechanisms are analyzed with high-resolution electron beam analytical techniques. Cathodoluminescence images are combined with electron backscattered diffraction maps in order to understand the interplay between cataclasis and crystal plasticity, which samples exhibit. Different microfabric regimes are investigated in order to discriminate between fault displacement caused by seismic slip or aseismic creep.

This work is a part of the project SPELEOTECT that investigates the Quaternary tectonic activity and recent dynamics of micro-displacements along major fault systems of the Eastern Alps recorded in caves. The aim of the project is building a database of the paleoseismic record of the Eastern Alps for regional earthquake hazard assessment.