Tracking aftershock sequences using empirical matched field processing

SUMMARY Extensive aftershock sequences present a significant problem to seismological data centres attempting produce near real-time comprehensive seismic event bulletins. An elevated number of events process and poorer performance automatic phase association algorithms can lead large delays in processing greatly increased human workload. Global monitoring is often performed using array stations at considerable distances from the involved. Empirical matched field (EMFP) narrow-frequency band signal technique that recognizes inter-sensor amplitude relations associated with wavefronts approaching sensor given direction. We demonstrate EMFP, template obtained first P arrival main shock alone, efficiently detect identify arrivals on subsequent zone exceptionally few false alarms (signals other sources). The empirical wavefield encodes all narrow-band observed for signal. These are also robust repeatable characteristics signals nearby events. EMFP detection statistic compares time incoming stream those sensitive very short-duration required characteristics. Significant deviations plane wavefront model typically degrade standard beamforming techniques enhance characterization EMFP. Waveform correlation perform poorly aftershocks earthquakes due between hypocentres wide range magnitudes source mechanisms. remote arrays mitigates these difficulties; nature procedure makes identification less signals’ temporal form spectral content. steering vectors derived reduce frequency dependency slowness vector estimates. This property helps us automatically screen out outside zone. Standard pipelines could be enhanced by including both plane-wave vectors. would maintain capability provide sensitivity resolution sources which we have calibrations.