Maximum earthquake magnitudes in the Aegean area constrained by tectonic moment release rates

Abstract

SUMMARY Seismic moment release is usually dominated by the largest but rarest events, making the estimation of seismic hazard inherently uncertain. This uncertainty can be reduced by combining long‐term tectonic deformation rates with short‐term recurrence rates. Here we adopt this strategy to estimate recurrence rates and maximum magnitudes for tectonic zones in the Aegean area. We first form a merged catalogue for historical and instrumentally recorded earthquakes in the Aegean, based on a recently published catalogue for Greece and surrounding areas covering the time period 550 BC–2000 AD, at varying degrees of completeness. The historical data are recalibrated to allow for changes in damping in seismic instruments around 1911. We divide the area up into zones that correspond to recent determinations of deformation rate from satellite data. In all zones we find that the Gutenberg–Richter (GR) law holds at low magnitudes. We use Akaike's information criterion to determine the best‐fitting distribution at high magnitudes, and classify the resulting frequency–magnitude distributions of the zones as critical (GR law), subcritical (gamma density distribution) or supercritical (‘characteristic’ earthquake model) where appropriate. We determine the ratio η of seismic to tectonic moment release rate. Low values of η (<0.5) corresponding to relatively aseismic deformation, are associated with higher b values (>1.0). The seismic and tectonic moment release rates are then combined to constrain recurrence rates and maximum credible magnitudes (in the range 6.7–7.6 mW where the results are well constrained) based on extrapolating the short‐term seismic data. With current earthquake data, many of the tectonic zones show a characteristic distribution that leads to an elevated probability of magnitudes around 7, but a reduced probability of larger magnitudes above this value when compared with the GR trend. A modification of the generalized gamma distribution is suggested to account for this, based on a finite statistical second moment for the seismic moment distribution.

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