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Abstract

An early detection of the presence of rupture directivity plays a major role in the correct estimation of ground motions and risks associated to the earthquake occurrence. We present here a simple method for a fast detection of rupture directivity, which may be additionally used to discriminate fault and auxiliary planes and have first estimations of important kinematic source parameters, such as rupture length and rupture time. Our method is based on the inversion of amplitude spectra from P-wave seismograms to derive the apparent duration at each station and on the successive modelling of its azimuthal behaviour. Synthetic waveforms are built assuming a spatial point source approximation, and the finite apparent duration of the spatial point source is interpreted in terms of rupture directivity. Since synthetic seismograms for a point source are calculated very quickly, the presence of directivity may be detected within few seconds, once a focal mechanism has been derived. The method is here first tested using synthetic datasets, both for linear and planar sources, and then successfully applied to recent Mw 6.2–6.8 shallow earthquakes in Peloponnese, Greece. The method is suitable for automated application and may be used to improve kinematic waveform modelling approaches.