An automated Rayleigh-wave detection algorithm

Abstract The desire to operate denser networks in order to monitor seismic activity at lower thresholds leads to greater emphasis on automated data processing. An algorithm for detecting and characterizing long-period Rayleigh-wave arrivals has been developed and tested. The routine continuously monitors all directions of approach to a station, in a manner similar to beamforming. The detector is based on cross-powers between the Hilbert-transformed vertical and rotated horizontal signals, so it is sensitive to both the power and polarization properties of the three-component wave field. Elliptically polarized Rayleigh arrivals are enhanced, while linearly polarized Love waves and body phases are suppressed. A test using one month of data from station ANMO demonstrated that this technique can, with high reliability, detect Rayleigh arrivals that are visible on the records. The measured arrival times and azimuths are accurate enough to permit automated association of the detections to events in a bulletin.