Earthquake recurrence parameters from seismic and geodetic strain rates in the eastern Mediterranean

Abstract

Although the parameters used in seismic hazard analyses imply a long-term seismic strain rate, they are usually not checked against such alternative estimates. In this study, we determine hazard parameters for the eastern Mediterranean (a-value, b-value, mmax and the corresponding long-term seismic moment rate Mseis0 consistent with seismicity data, tectonic information and geodetic strain rates. The dense data coverage in this region permits a detailed comparison of the horizontal seismic strain rate field, εs, as recorded in the 500-yr long historical catalogue and the tectonic strain rate field, εg, measured geodetically. We find that εs, is very similar in style over all magnitude ranges within each different tectonic regime in the study region. Furthermore, εs is similar in style to εg. Except along the Hellenic Arc, εs is consistent with εg in amplitude. We verify that for the high strain rates accommodated in the eastern Mediterranean and historical catalogues spanning at least 100-200 yr, ̇εs should reflect the long-term seismic strain release when averaged over each tectonic zone. To estimate such seismic strain reliably, accurate knowledge about the rates of recurrence of intermediate size events (Mw = 4.5-6.5) is needed. For b ≥ 1, these events can accommodate up to 60 per cent of the strain. The combined analysis of ̇εg and εs provides an estimate of the seismic/total strain. The major strike-slip zones in the region, the Northern Anatolian Fault and the Kephalonian Fault, experience little to negligible aseismic deformation. In the remaining eastern Mediterranean up to 10-30 per cent of the total deformation is aseismic. The Hellenic Trench is largely uncoupled, with at least 50 per cent and up to 90 per cent of the compressive strain released aseismically. Only the extensional component of strain at the eastern end of this trench appears significantly seismically active. © 2004 RAS.