Deformation patterns associated with the M5.9 Athens (Greece) earthquake of 7 September 1999

Abstract

The static displacement field of the Athens 1999 earthquake has been numerically modeled by a BEM method and analysed from SAR interferometry images with compatible results: (a) for a fault that reaches the surface the subsidence field coincides with the hangingwall domain of the Fili neotectonic normal fault with maximum amplitude, dmax, 5.5–7 cm, which is consistent with the possibly co-seismic displacement of 6–10 cm observed in the field, the average fault dislocation of 5–8 cm found by the application of circular source models, and the displacement up to ∼6 cm predicted by empirical relations between magnitude and displacement; the field of uplift covers the footwall domain of the fault with dmax∼1.5 cm;d gradually decreases with distance from the fault at a gradient of ∼ 0.4 cm/km, (b) for a blind fault dmax is only 1.8 and 0.3 cm in the hangingwall and footwall, respectively, and the decay gradient becomes ∼0.15 cm/km, (c) the total deformation area is ∼15 km × 15 km and the Fili fault, with a preferred mean dip of 60°, constitutes the natural boundary between the subsidence and uplift areas. The macroseismic field pattern is similar with that of the static ground deformation. The majority of intensity values ≥VI (MM and EMS-98 scales), are distributed within the hangingwall of the Fili fault, while the highest intensities (VIII and IX) concentrate very close to the Fili fault within its hangingwall domain. A gradual decrease of the intensities with the distance from the Fili fault is evident. Because of the similarity between the intensity distribution pattern and the static ground deformation pattern, we make the hypothesis that the latter predicts well enough the main characteristics of the former although the ground displacement is dominated by relatively low frequency as compared to the ground acceleration.