The Source Mechanism of the Athens Earthquake, September 7, 1999, Estimated from <Emphasis Type="Bold">P Seismograms Recorded at Long Range

On 7 September, 1999, an earthquake (5.8 m<Subscript>b</Subscript> <Superscript>USGS</Superscript>)took place about 20 km from the centre of Athens, until then a seismically quiet region ofeastern Greece. Considerable damage ranging from rock falls to the collapse of reinforcedconcrete structures was reported in the city and surrounding area. No surface break which couldbe directly attributed to rupture on the fault plane was mapped. We use the relativeamplitude method and forward modelling of broadband <Emphasis Type="Bold">P seismogramsrecorded at long range to produce a two-dimensional model of the source. We conclude that the earthquake tookplace on a south-west dipping normal fault at a depth of 10 km. This implies that the depthof the seismogenic zone in the area is comparable to other more active regions of Greece.The rupture speed (2.1 km/s) and stress drop (0.54 MPa) are low and are typical of earthquakesin a tectonic environment dominated by high rates of extension. The estimated seismicmoment is 6.014 × 10<Superscript>17</Superscript> N m. We have investigated reported rupture directivity and thepossibility of a circular rupture is also examined. Extrapolation of the fault plane to the freesurface suggests that the earthquake took place on a structure associated with the Fili fault. Copyright Kluwer Academic Publishers 2002