A p-wave based methodology for rapid, real time determination of seismic moment, fault extent and stress drop

The source characterization for earthquake early warning systems is generally based on the measurement of the peak amplitude or period parameters measured along the early portion of the recorded P and S-wave signals (3 or 4 seconds). These parameters are related to the earthquake size or to the peak ground shaking amplitude through empirical scaling relationships. Standard methodologies for real-time applications typically assume a point-source model of the earthquake source and this assumption may be inadequate to describe the source of large earthquakes, possibly introducing significant biases in the real-time estimation of earthquake magnitude and ground shaking prediction. To avoid magnitude underestimation, the use of limited time windows has been recently replaced by the concept of expanding time windows, showing that standard parameters and existing empirical relationships can be used also for very large earthquakes, provided that appropriate time windows are selected for the parameter measurement. Following the concept of expanding P-wave time windows, here we propose a straightforward methodology, based on the P-wave amplitude, to quickly characterize the finite extension of the seismic source and its scalar moment. In particular, here we investigate whether and how the progressive and evolutionary measurement of early warning parameters can provide a rapid estimate of the event magnitude and of the expected length of the rupture. The methodology we propose is computationally simple and does not require complex signal processing. It is expected to provide a rapid and robust estimation of the source extent, which can significantly improve the accuracy of the ground shaking prediction during the occurrence of very large events.