Source parameters and tectonic interpretation of recent earthquakes (1995-1997) in the Pannonian basin

From January 1995 to December 1997, about 74 earthquakes were located in th e Pannonian basin and digitally recorded by a recently established network of seismological stations in Hungary. On reviewing the notable events, abou t 12 earthquakes were reported as felt with maximum intensity varying betwe en 4 and 6 MSK, The dynamic source parameters of these earthquakes have bee n derived from P-wave displacement spectra. The displacement source spectra obtained are characterised by relatively small values of corner frequency (f(0)) ranging between 2.5 and 10 Hz. The seismic moments change from 1.48 x 10(20) to 1.3 x 10(23) dyne cm, stress drops from 0.25 to 76.75 bar, faul t length from 0.42 to 1.7 km and relative displacement from 0.05 to 15.35 c m, The estimated source parameters suggest a good agreement with the scalin g law for small earthquakes. The small values of stress drops in the studie d earthquakes can be attributed to the low strength of crustal materials in the Pannonian basin. However, the values of stress drops are not different for earthquake with thrust or normal faulting focal mechanism solutions. I t can be speculated that an increase of the seismic activity in the Pannoni an basin can be predicted in the long run because extensional development c eased and structural inversion is in progress. Seismic hazard assessment is a delicate job due to the inadequate knowledge of the seismo-active faults , particularly in the interior part of the Pannonian basin. (C) 2000 Elsevi er Science Ltd. All rights reserved.